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| [GMCnet] Disc brake project still in failure mode [message #281955] |
Sun, 12 July 2015 19:19  |
Neil Fonville
Messages: 68
Registered: May 2014
Karma: 0
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Member |
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I'm back to working on my brake project and just not getting it done. Still have soft pedal and it's takes way too much distance to stop. It's far worse from where is started with 2 Disc and 4 Drums that were not working good.
Here is rehash of what steps I have taken and maybe someone can help get me back on track. I'm still amazed I can't find a mechanic/shop in the Dallas area that could help me with my projects.
First I installed the Manny rear disc brake kit. Install was straight forward.
Bleed the system with the standard 2 man pump and release fluid method. Never felt right and the vehicle was not even remotely drivable.
Replaced proportion valve with Disc/Disc model.
Removed OEM MC and replaced MC with new one from O'rilly. Used the P30 (PN NMC1668).
Did not bench bleed. Bleed with 2 man pump and release fluid. Still pedal too soft and not drivable. Removed MC and put on bench and found front chamber not pushing fluid.
Replaced with another new MC from O'rilly same part number. Pedal pumped up tighter but it leaked between the fluid reservoir and cast metal piston. Still not drivable.
Replaced MC with new one from Autozone (PN NM1641 ). Purchased the Hupy bleeder. Bleed according to his directions which is RR moving to LF. Removed lots of air and pumped about 1/2 gallon of fluid through the system. Still not drivable, pedal too soft and vehicle does not stop. From 30 to zero takes about 1/4 mile.
So how do I go about troubleshooting the individual components? How do I test hydraulic pressure?
I'm hoping for someone to give me a systematic approach to resolve this and get this working.
Yes, I have spoke with Manny and I really don't think any of the calipers are defective.
Thanks Neil Fonville
1975 GMC II
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1975 GMC II
Allen, TX
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| Re: [GMCnet] Disc brake project still in failure mode [message #281956 is a reply to message #281955] |
Sun, 12 July 2015 19:41  |
Hal StClair
Messages: 971
Registered: March 2013
Location: Rio Rancho NM
Karma: -12
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Senior Member |
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I think I'd check the run out on the rear rotors. There may be enough movement to be pushing the caliper pistons back. If that's the problem and you can't resolve the run out, a 2 lb residual check valve in the rear brake line may be your answer.
Hal
"I enjoy talking to you. Your mind appeals to me. It resembles my own mind, except you happen to be insane."
1977 Royale 101348,
1977 Royale 101586, Diesel powered,
1974 Eagle Bus 45',w/slideout,
Rio Rancho, NM
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| Re: [GMCnet] Disc brake project still in failure mode [message #281957 is a reply to message #281955] |
Sun, 12 July 2015 20:01 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Neil,
There are so MANY possibilities that I don't know where to start (and I'm
in the midst of a Hydroboost installation on my 1-Ton+Manny Brakes equipped
23', which has had just about every brake combination you can think of.
I'm just going to mention some items to be sure you've addressed all of
them:
Booster -- what's its' status?
Vacuum seal between the booster and MC -- correct seal, correctly installed?
Push rod length -- have you measured it and set about 0.005" clearance?
Flex hoses (on front, obviously you installed new rear with Manny Brakes).
How much have you driven the coach to break in the pads? It an be amazing
how much improvement occurs in the first 100-200 miles.
Perhaps the most useful tool for you would be one of these:
http://www.amazon.com/SSBC-A1704-Brake-Pressure-Gauge/dp/B003VYVFSS/ref=sr_1_1?ie=UTF8&qid=1436748655&sr=8-1&keywords=brake+pressure+gauge
That kit from Stainless Steel Brakes includes a set of adapters for 'most
any caliper or wheel cylinder to allow you to attach the included 0-1600
psi gauge. With that you can measure the hydraulic line pressure at a
front and a rear caliper. Unless your booster/MC/etc. can provide 600+ psi
of line pressure, you will NOT have good brakes. Having a visual
indication of the results of each action you take will be valuable in
solving your problem. You'd like to have 1000+ psi, but it's rare on a GMC.
HTH,
Ken H.
On Sun, Jul 12, 2015 at 8:19 PM, Neil Fonville wrote:
> I'm back to working on my brake project and just not getting it done.
> Still have soft pedal and it's takes way too much distance to stop. It's
> far worse from where is started with 2 Disc and 4 Drums that were not
> working good.
>
> Here is rehash of what steps I have taken and maybe someone can help get
> me back on track. I'm still amazed I can't find a mechanic/shop in the
> Dallas area that could help me with my projects.
>
> First I installed the Manny rear disc brake kit. Install was straight
> forward.
> Bleed the system with the standard 2 man pump and release fluid method.
> Never felt right and the vehicle was not even remotely drivable.
> Replaced proportion valve with Disc/Disc model.
> Removed OEM MC and replaced MC with new one from O'rilly. Used the P30 (PN
> NMC1668).
> Did not bench bleed. Bleed with 2 man pump and release fluid. Still
> pedal too soft and not drivable. Removed MC and put on bench and found
> front chamber not pushing fluid.
> Replaced with another new MC from O'rilly same part number. Pedal pumped
> up tighter but it leaked between the fluid reservoir and cast metal
> piston. Still not drivable.
> Replaced MC with new one from Autozone (PN NM1641 ). Purchased the Hupy
> bleeder. Bleed according to his directions which is RR moving to LF.
> Removed lots of air and pumped about 1/2 gallon of fluid through the
> system. Still not drivable, pedal too soft and vehicle does not stop.
> From 30 to zero takes about 1/4 mile.
>
> So how do I go about troubleshooting the individual components? How do I
> test hydraulic pressure?
>
> I'm hoping for someone to give me a systematic approach to resolve this
> and get this working.
>
> Yes, I have spoke with Manny and I really don't think any of the calipers
> are defective.
>
> Thanks Neil Fonville
> 1975 GMC II
>
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Disc brake project still in failure mode [message #281958 is a reply to message #281955] |
Sun, 12 July 2015 20:19 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Neil, Jack up your coach and remove the wheels and tires. I surmise here
that you have the rear/rear calipers with parking brakes. I have found that
if the short lug protruding from the inside brake pad is not indexed with
the caliper piston that the pad will not sit squarely onto the piston, and
there will be way too much space between the components. That pad material
should ride in slight contact with the rotor when they are broken in, and
there should also be no visible space between the caliper piston and the
backing plate on the pad. Same on all disc/rotors. If you broke the
retaining clip off the back of the pad and left anything sticking up in the
middle of the pad where the rivet is, the pad should be removed and the
rivet head ground down. Also you need to pre adjust the parking brake
ratcheting mechanism to eliminate all the space. If you have clearance
where I have just described, you will use up available pedal travel taking
up that clearance before any pressure can build up in the system. Low
pedal, and poor stopping is the result.
Jim Hupy
Salem, Oregon
78 GMC ROYALE 403
On Jul 12, 2015 5:20 PM, "Neil Fonville" wrote:
> I'm back to working on my brake project and just not getting it done.
> Still have soft pedal and it's takes way too much distance to stop. It's
> far worse from where is started with 2 Disc and 4 Drums that were not
> working good.
>
> Here is rehash of what steps I have taken and maybe someone can help get
> me back on track. I'm still amazed I can't find a mechanic/shop in the
> Dallas area that could help me with my projects.
>
> First I installed the Manny rear disc brake kit. Install was straight
> forward.
> Bleed the system with the standard 2 man pump and release fluid method.
> Never felt right and the vehicle was not even remotely drivable.
> Replaced proportion valve with Disc/Disc model.
> Removed OEM MC and replaced MC with new one from O'rilly. Used the P30 (PN
> NMC1668).
> Did not bench bleed. Bleed with 2 man pump and release fluid. Still
> pedal too soft and not drivable. Removed MC and put on bench and found
> front chamber not pushing fluid.
> Replaced with another new MC from O'rilly same part number. Pedal pumped
> up tighter but it leaked between the fluid reservoir and cast metal
> piston. Still not drivable.
> Replaced MC with new one from Autozone (PN NM1641 ). Purchased the Hupy
> bleeder. Bleed according to his directions which is RR moving to LF.
> Removed lots of air and pumped about 1/2 gallon of fluid through the
> system. Still not drivable, pedal too soft and vehicle does not stop.
> From 30 to zero takes about 1/4 mile.
>
> So how do I go about troubleshooting the individual components? How do I
> test hydraulic pressure?
>
> I'm hoping for someone to give me a systematic approach to resolve this
> and get this working.
>
> Yes, I have spoke with Manny and I really don't think any of the calipers
> are defective.
>
> Thanks Neil Fonville
> 1975 GMC II
>
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Disc brake project still in failure mode [message #281961 is a reply to message #281955] |
Sun, 12 July 2015 20:38 |
 |
wally
Messages: 643
Registered: August 2004
Location: Omaha Nebraska
Karma: 5
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Senior Member |
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Neil Fonville wrote on Sun, 12 July 2015 19:19I'm back to working on my brake project and just not getting it done. Still have soft pedal and it's takes way too much distance to stop. It's far worse from where is started with 2 Disc and 4 Drums that were not working good.
Here is rehash of what steps I have taken and maybe someone can help get me back on track. I'm still amazed I can't find a mechanic/shop in the Dallas area that could help me with my projects.
First I installed the Manny rear disc brake kit. Install was straight forward.
Bleed the system with the standard 2 man pump and release fluid method. Never felt right and the vehicle was not even remotely drivable.
Replaced proportion valve with Disc/Disc model.
Removed OEM MC and replaced MC with new one from O'rilly. Used the P30 (PN NMC1668).
Did not bench bleed. Bleed with 2 man pump and release fluid. Still pedal too soft and not drivable. Removed MC and put on bench and found front chamber not pushing fluid.
Replaced with another new MC from O'rilly same part number. Pedal pumped up tighter but it leaked between the fluid reservoir and cast metal piston. Still not drivable.
Replaced MC with new one from Autozone (PN NM1641 ). Purchased the Hupy bleeder. Bleed according to his directions which is RR moving to LF. Removed lots of air and pumped about 1/2 gallon of fluid through the system. Still not drivable, pedal too soft and vehicle does not stop. From 30 to zero takes about 1/4 mile.
So how do I go about troubleshooting the individual components? How do I test hydraulic pressure?
I'm hoping for someone to give me a systematic approach to resolve this and get this working.
Yes, I have spoke with Manny and I really don't think any of the calipers are defective.
Thanks Neil Fonville
1975 GMC II
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Neil, I feel for ya. I went through gyrations getting all the air out of P master cylinders and the rest of the system after air got pushed in. Went as far as buying a 1992 P Models service manual to get GM's method of bench bleeding. Short version is plug both ports and start with the front of the master slightly down then when the air seems out tilt the front slightly up and go and it again. When the air is finally out the pedal won't be "soft". Here is a scan of the manual page.
http://www.gmcmhphotos.com/photos/p-30-master-cylinder-disassembled/p58428-1992-p-model-master.html
Here is the contraption I made to tilt the darn things while bench bleeding.
http://wallyandsue.blogspot.com/2015/06/p-30-master-cylinder-bench-bleed-and.html
I thought the first master was bad but it wasn't. I did take it apart to see after the second acted exactly the same and couldn't find anything wrong, Actually its built like a hydraulic cylinder with orings and teflon backup rings, no ports that a cup would get torn on and the valves are spring loaded closed until the piston is in the return position and tilts them open.
HTH
Wally Anderson
Omaha NE
75 Glenbrook
[Updated on: Sun, 12 July 2015 20:47] Report message to a moderator |
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| Re: [GMCnet] Disc brake project still in failure mode [message #281976 is a reply to message #281961] |
Mon, 13 July 2015 00:29 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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If your caliper is mountes ar 3-9 o clock, you need to tilt it so the
bleder valve will be at 12 oclock.
Look at location of front caliper .
On Sun, Jul 12, 2015 at 6:38 PM, Wally Anderson
wrote:
> Neil Fonville wrote on Sun, 12 July 2015 19:19
>> I'm back to working on my brake project and just not getting it done.
> Still have soft pedal and it's takes way too much distance to stop. It's
>> far worse from where is started with 2 Disc and 4 Drums that were not
> working good.
>>
>> Here is rehash of what steps I have taken and maybe someone can help get
> me back on track. I'm still amazed I can't find a mechanic/shop in the
>> Dallas area that could help me with my projects.
>>
>> First I installed the Manny rear disc brake kit. Install was straight
> forward.
>> Bleed the system with the standard 2 man pump and release fluid method.
> Never felt right and the vehicle was not even remotely drivable.
>> Replaced proportion valve with Disc/Disc model.
>> Removed OEM MC and replaced MC with new one from O'rilly. Used the P30
> (PN NMC1668).
>> Did not bench bleed. Bleed with 2 man pump and release fluid. Still
> pedal too soft and not drivable. Removed MC and put on bench and found
>> front chamber not pushing fluid.
>> Replaced with another new MC from O'rilly same part number. Pedal
> pumped up tighter but it leaked between the fluid reservoir and cast metal
>> piston. Still not drivable.
>> Replaced MC with new one from Autozone (PN NM1641 ). Purchased the Hupy
> bleeder. Bleed according to his directions which is RR moving to LF.
>> Removed lots of air and pumped about 1/2 gallon of fluid through the
> system. Still not drivable, pedal too soft and vehicle does not stop.
> From 30
>> to zero takes about 1/4 mile.
>>
>> So how do I go about troubleshooting the individual components? How do
> I test hydraulic pressure?
>>
>> I'm hoping for someone to give me a systematic approach to resolve this
> and get this working.
>>
>> Yes, I have spoke with Manny and I really don't think any of the
> calipers are defective.
>>
>> Thanks Neil Fonville
>> 1975 GMC II
>>
>>
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> Neil, I feel for ya. I went through gyrations getting all the air out of P
> master cylinders and the rest of the system after air got pushed in. Went
> as far as buying a 1992 P Models service manual to get GM's method of
> bench bleeding. Short version is start with the front of the master slightly
> down then when the air seems out tilt the front slightly up and go and it
> again. When the air is finally out the pedal won't be "soft". Here is a scan
> of the manual page.
>
> http://www.gmcmhphotos.com/photos/p-30-master-cylinder-disassembled/p58428-1992-p-model-master.html
> Here is the contraption I made to tilt the darn things while bench
> bleeding.
>
> http://wallyandsue.blogspot.com/2015/06/p-30-master-cylinder-bench-bleed-and.html
> I thought the first master was bad but it wasn't. I did take it apart to
> see after the second acted exactly the same and couldn't find anything
> wrong,
> Actually its built like a hydraulic cylinder with orings and teflon backup
> rings, no ports that a cup would get torn on and the valves are spring
> loaded closed until the piston is in the return position and tilts them
> open.
> HTH
> --
> Wally Anderson
> 1975 Glenbrook
> Megasquirt 455 port injection science project
> Omaha Nebraska
> Greater Midwest Classics
> GMCES
> http://wallyandsue.blogspot.com/
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] Disc brake project still in failure mode [message #281980 is a reply to message #281958] |
Mon, 13 July 2015 06:59 |
Neil Fonville
Messages: 68
Registered: May 2014
Karma: 0
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Member |
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Jim,
I will inspect for the gaps. With one set of the wheels off on one side
at a time, I don¹t see any gap but will look much more closely.
How important is the parking brake being setup correctly initially. I
have not done that yet. I was planning on that being the last step?
Thanks,
Neil
On 7/12/15, 8:19 PM, "Gmclist on behalf of James Hupy"
wrote:
> Neil, Jack up your coach and remove the wheels and tires. I surmise here
> that you have the rear/rear calipers with parking brakes. I have found
> that
> if the short lug protruding from the inside brake pad is not indexed with
> the caliper piston that the pad will not sit squarely onto the piston, and
> there will be way too much space between the components. That pad material
> should ride in slight contact with the rotor when they are broken in, and
> there should also be no visible space between the caliper piston and the
> backing plate on the pad. Same on all disc/rotors. If you broke the
> retaining clip off the back of the pad and left anything sticking up in
> the
> middle of the pad where the rivet is, the pad should be removed and the
> rivet head ground down. Also you need to pre adjust the parking brake
> ratcheting mechanism to eliminate all the space. If you have clearance
> where I have just described, you will use up available pedal travel taking
> up that clearance before any pressure can build up in the system. Low
> pedal, and poor stopping is the result.
> Jim Hupy
> Salem, Oregon
> 78 GMC ROYALE 403
> On Jul 12, 2015 5:20 PM, "Neil Fonville" wrote:
>
>> I'm back to working on my brake project and just not getting it done.
>> Still have soft pedal and it's takes way too much distance to stop.
>> It's
>> far worse from where is started with 2 Disc and 4 Drums that were not
>> working good.
>>
>> Here is rehash of what steps I have taken and maybe someone can help get
>> me back on track. I'm still amazed I can't find a mechanic/shop in the
>> Dallas area that could help me with my projects.
>>
>> First I installed the Manny rear disc brake kit. Install was straight
>> forward.
>> Bleed the system with the standard 2 man pump and release fluid method.
>> Never felt right and the vehicle was not even remotely drivable.
>> Replaced proportion valve with Disc/Disc model.
>> Removed OEM MC and replaced MC with new one from O'rilly. Used the P30
>> (PN
>> NMC1668).
>> Did not bench bleed. Bleed with 2 man pump and release fluid. Still
>> pedal too soft and not drivable. Removed MC and put on bench and found
>> front chamber not pushing fluid.
>> Replaced with another new MC from O'rilly same part number. Pedal
>> pumped
>> up tighter but it leaked between the fluid reservoir and cast metal
>> piston. Still not drivable.
>> Replaced MC with new one from Autozone (PN NM1641 ). Purchased the Hupy
>> bleeder. Bleed according to his directions which is RR moving to LF.
>> Removed lots of air and pumped about 1/2 gallon of fluid through the
>> system. Still not drivable, pedal too soft and vehicle does not stop.
>> From 30 to zero takes about 1/4 mile.
>>
>> So how do I go about troubleshooting the individual components? How do
>> I
>> test hydraulic pressure?
>>
>> I'm hoping for someone to give me a systematic approach to resolve this
>> and get this working.
>>
>> Yes, I have spoke with Manny and I really don't think any of the
>> calipers
>> are defective.
>>
>> Thanks Neil Fonville
>> 1975 GMC II
>>
>>
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
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1975 GMC II
Allen, TX
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| Re: [GMCnet] Disc brake project still in failure mode [message #281981 is a reply to message #281957] |
Mon, 13 July 2015 06:56 |
Neil Fonville
Messages: 68
Registered: May 2014
Karma: 0
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Member |
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Ken, I have a few questions:
I did the procedure of bending the support bracket so I have the pushrod
gap the thickness of the bracket in pedal play. That does not bother me
as it¹s so slight. But you discuss a vacuum seal which I don¹t really
understand. The vacuum itself stays in the booster right? There is no
vacuum connection to the MC? Booster seems to be working as the pedal is
much harder when the engine is not running. What am I not understanding
about the booster to MC connection?
I¹m glad you mention the pressure gauge. I purchased that but have not
used it yet but will. Do you have to bleed for it or does it self bleed
and remove the air?
I will closely inspect the front hoses.
Thanks,
Neil
On 7/12/15, 8:01 PM, "Gmclist on behalf of Ken Henderson"
wrote:
> Neil,
>
> There are so MANY possibilities that I don't know where to start (and I'm
> in the midst of a Hydroboost installation on my 1-Ton+Manny Brakes
> equipped
> 23', which has had just about every brake combination you can think of.
>
> I'm just going to mention some items to be sure you've addressed all of
> them:
>
> Booster -- what's its' status?
>
> Vacuum seal between the booster and MC -- correct seal, correctly
> installed?
>
> Push rod length -- have you measured it and set about 0.005" clearance?
>
> Flex hoses (on front, obviously you installed new rear with Manny Brakes).
>
> How much have you driven the coach to break in the pads? It an be amazing
> how much improvement occurs in the first 100-200 miles.
>
> Perhaps the most useful tool for you would be one of these:
>
> http://www.amazon.com/SSBC-A1704-Brake-Pressure-Gauge/dp/B003VYVFSS/ref=sr
> _1_1?ie=UTF8&qid=1436748655&sr=8-1&keywords=brake+pressure+gauge
>
> That kit from Stainless Steel Brakes includes a set of adapters for 'most
> any caliper or wheel cylinder to allow you to attach the included 0-1600
> psi gauge. With that you can measure the hydraulic line pressure at a
> front and a rear caliper. Unless your booster/MC/etc. can provide 600+
> psi
> of line pressure, you will NOT have good brakes. Having a visual
> indication of the results of each action you take will be valuable in
> solving your problem. You'd like to have 1000+ psi, but it's rare on a
> GMC.
>
> HTH,
>
> Ken H.
>
>
> On Sun, Jul 12, 2015 at 8:19 PM, Neil Fonville
> wrote:
>
>> I'm back to working on my brake project and just not getting it done.
>> Still have soft pedal and it's takes way too much distance to stop.
>> It's
>> far worse from where is started with 2 Disc and 4 Drums that were not
>> working good.
>>
>> Here is rehash of what steps I have taken and maybe someone can help get
>> me back on track. I'm still amazed I can't find a mechanic/shop in the
>> Dallas area that could help me with my projects.
>>
>> First I installed the Manny rear disc brake kit. Install was straight
>> forward.
>> Bleed the system with the standard 2 man pump and release fluid method.
>> Never felt right and the vehicle was not even remotely drivable.
>> Replaced proportion valve with Disc/Disc model.
>> Removed OEM MC and replaced MC with new one from O'rilly. Used the P30
>> (PN
>> NMC1668).
>> Did not bench bleed. Bleed with 2 man pump and release fluid. Still
>> pedal too soft and not drivable. Removed MC and put on bench and found
>> front chamber not pushing fluid.
>> Replaced with another new MC from O'rilly same part number. Pedal
>> pumped
>> up tighter but it leaked between the fluid reservoir and cast metal
>> piston. Still not drivable.
>> Replaced MC with new one from Autozone (PN NM1641 ). Purchased the Hupy
>> bleeder. Bleed according to his directions which is RR moving to LF.
>> Removed lots of air and pumped about 1/2 gallon of fluid through the
>> system. Still not drivable, pedal too soft and vehicle does not stop.
>> From 30 to zero takes about 1/4 mile.
>>
>> So how do I go about troubleshooting the individual components? How do
>> I
>> test hydraulic pressure?
>>
>> I'm hoping for someone to give me a systematic approach to resolve this
>> and get this working.
>>
>> Yes, I have spoke with Manny and I really don't think any of the
>> calipers
>> are defective.
>>
>> Thanks Neil Fonville
>> 1975 GMC II
>>
>>
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
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Unsubscribe or Change List Options:
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1975 GMC II
Allen, TX
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| Re: [GMCnet] Disc brake project still in failure mode [message #281984 is a reply to message #281981] |
Mon, 13 July 2015 07:13 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Neil,
In the recess of the booster, where the MC seats, around the plastic
carrier for the MC push rod, there should be a rubber seal with radial
indentations. That seal is there to retain the vacuum in the forward
chamber of the booster. When assembled normally (with the bracket on the
forward side of the MC ears), the nose of the MC keeps that seal in
position. Now that you've moved the MC 0.100" or so away from the booster,
that seal is no longer retained and MAY be losing vacuum. Dave Lenzi makes
a little nylon washer to fit between the MC and the seal restore the
retaining force; I dont' know whether he sells them separately from his
booster, but you could easily make something similar.
Further compounding the MC/Booster interface is the fact that many of the
boosters being promoted for us today are metrically dimensioned. That
results in the MC seating less snugly in the booster than it should. Dave
considers that a significant problem and makes a centering ring. I'm not
as sure it's a problem because the assemblies I've seen (far fewer than
Dave has) are well centered by the mounting bolts. But you should be aware
of it.
Did you adjust the length of your MC push rod to compensate for the 0.100"
"spacer" the bracket now forms between the MC and the booster? If not, you
will definitely have a low pedal, regardless of the "tightness" of the rest
of the system. Here's how I measure the new push rod:
http://www.gmcmhphotos.com/photos/g6289-master-cylinder-pushrod-gauge.html
HTH,
Ken H.
On Mon, Jul 13, 2015 at 7:56 AM, Neil Fonville wrote:
> Ken, I have a few questions:
>
> I did the procedure of bending the support bracket so I have the pushrod
> gap the thickness of the bracket in pedal play. That does not bother me
> as it¹s so slight. But you discuss a vacuum seal which I don¹t really
> understand. The vacuum itself stays in the booster right? There is no
> vacuum connection to the MC? Booster seems to be working as the pedal is
> much harder when the engine is not running. What am I not understanding
> about the booster to MC connection?
>
> I¹m glad you mention the pressure gauge. I purchased that but have not
> used it yet but will. Do you have to bleed for it or does it self bleed
> and remove the air?
>
> I will closely inspect the front hoses.
>
> Thanks,
> Neil
>
>
>
> On 7/12/15, 8:01 PM, "Gmclist on behalf of Ken Henderson"
>
> wrote:
>
>> Neil,
>>
>> There are so MANY possibilities that I don't know where to start (and I'm
>> in the midst of a Hydroboost installation on my 1-Ton+Manny Brakes
>> equipped
>> 23', which has had just about every brake combination you can think of.
>>
>> I'm just going to mention some items to be sure you've addressed all of
>> them:
>>
>> Booster -- what's its' status?
>>
>> Vacuum seal between the booster and MC -- correct seal, correctly
>> installed?
>>
>> Push rod length -- have you measured it and set about 0.005" clearance?
>>
>> Flex hoses (on front, obviously you installed new rear with Manny Brakes).
>>
>> How much have you driven the coach to break in the pads? It an be amazing
>> how much improvement occurs in the first 100-200 miles.
>>
>> Perhaps the most useful tool for you would be one of these:
>>
>>
> http://www.amazon.com/SSBC-A1704-Brake-Pressure-Gauge/dp/B003VYVFSS/ref=sr
>> _1_1?ie=UTF8&qid=1436748655&sr=8-1&keywords=brake+pressure+gauge
>>
>> That kit from Stainless Steel Brakes includes a set of adapters for 'most
>> any caliper or wheel cylinder to allow you to attach the included 0-1600
>> psi gauge. With that you can measure the hydraulic line pressure at a
>> front and a rear caliper. Unless your booster/MC/etc. can provide 600+
>> psi
>> of line pressure, you will NOT have good brakes. Having a visual
>> indication of the results of each action you take will be valuable in
>> solving your problem. You'd like to have 1000+ psi, but it's rare on a
>> GMC.
>>
>> HTH,
>>
>> Ken H.
>>
>>
>> On Sun, Jul 12, 2015 at 8:19 PM, Neil Fonville
>> wrote:
>>
>>> I'm back to working on my brake project and just not getting it done.
>>> Still have soft pedal and it's takes way too much distance to stop.
>>> It's
>>> far worse from where is started with 2 Disc and 4 Drums that were not
>>> working good.
>>>
>>> Here is rehash of what steps I have taken and maybe someone can help get
>>> me back on track. I'm still amazed I can't find a mechanic/shop in the
>>> Dallas area that could help me with my projects.
>>>
>>> First I installed the Manny rear disc brake kit. Install was straight
>>> forward.
>>> Bleed the system with the standard 2 man pump and release fluid method.
>>> Never felt right and the vehicle was not even remotely drivable.
>>> Replaced proportion valve with Disc/Disc model.
>>> Removed OEM MC and replaced MC with new one from O'rilly. Used the P30
>>> (PN
>>> NMC1668).
>>> Did not bench bleed. Bleed with 2 man pump and release fluid. Still
>>> pedal too soft and not drivable. Removed MC and put on bench and found
>>> front chamber not pushing fluid.
>>> Replaced with another new MC from O'rilly same part number. Pedal
>>> pumped
>>> up tighter but it leaked between the fluid reservoir and cast metal
>>> piston. Still not drivable.
>>> Replaced MC with new one from Autozone (PN NM1641 ). Purchased the Hupy
>>> bleeder. Bleed according to his directions which is RR moving to LF.
>>> Removed lots of air and pumped about 1/2 gallon of fluid through the
>>> system. Still not drivable, pedal too soft and vehicle does not stop.
>>> From 30 to zero takes about 1/4 mile.
>>>
>>> So how do I go about troubleshooting the individual components? How do
>>> I
>>> test hydraulic pressure?
>>>
>>> I'm hoping for someone to give me a systematic approach to resolve this
>>> and get this working.
>>>
>>> Yes, I have spoke with Manny and I really don't think any of the
>>> calipers
>>> are defective.
>>>
>>> Thanks Neil Fonville
>>> 1975 GMC II
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
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> _______________________________________________
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Disc brake project still in failure mode [message #281986 is a reply to message #281955] |
Mon, 13 July 2015 07:58 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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A cursory read through this thread doesn't note that you've bled the brakes with a power bleeder. I have had zilch success with the two man procedure, and not a lot more with a vacuum bleeder. Local friend has a power bleeder made by Jim Hupy which is, to me, a PIA to get on correctly, but when it's properly working, it bleeds the brakes correctly. Solid pedal, and the coach will stop. My coach has drum rears with floating plates using the kit provided by Applied - I believe Tom Pryor actually figured it out.
My SOB - long gone - on a Chev P30 chassis used a hydroboost system. the parts sre cheap and easy to come by... but I don't see any way to set up a reservoir for engine failure situations. It >will< stop, if you anchor your tail in the seat and clomp down hard with both feet, much like the stock system.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Disc brake project still in failure mode [message #281989 is a reply to message #281980] |
Mon, 13 July 2015 08:35 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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Senior Member |
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Neil Fonville wrote on Mon, 13 July 2015 06:59...
How important is the parking brake being setup correctly initially. I
have not done that yet. I was planning on that being the last step?...
Very important Neil. The adjustment determines how far the caliper piston has to travel in order to begin applying pressure. The cars that caliper came with were supposed to set the parking brake EVERY TIME THEY PARKED in order to keep it in adjustment. Excessive travel means more fluid required.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: [GMCnet] Disc brake project still in failure mode [message #281991 is a reply to message #281980] |
Mon, 13 July 2015 09:04 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Neil, I usually do not even install the ebrake cables until I have debugged
the service brakes and they have enough miles on them to break in the
linings. I do, however adjust the ratchets that move the caliper piston out
towards the rotor. You need to be very diligent in indexing that little lug
on the pad backing plate into the caliper piston. SOMETIMES the caliper
piston will rotate enough so that the detent in the piston will not align
with the lug. If you find this to be the case, the piston must be rotated
back to index with the lug. It is quite difficult to turn. I use a big pair
of channel lock pliers and a piece of gasket material scrap left over from
my bleeders to protect the piston from plier damage. On the ebrake cables,
I make up custom ones of the exact correct length for the outer sheath
instead of the supplied threaded sleeve and jam nuts used with the old
rusty, kinked, original outer cables. Those inner cables need to move
freely with no binding to work correctly.
Jim Hupy
On Jul 13, 2015 4:59 AM, "Neil Fonville" wrote:
> Jim,
>
> I will inspect for the gaps. With one set of the wheels off on one side
> at a time, I don¹t see any gap but will look much more closely.
>
> How important is the parking brake being setup correctly initially. I
> have not done that yet. I was planning on that being the last step?
>
> Thanks,
> Neil
>
> On 7/12/15, 8:19 PM, "Gmclist on behalf of James Hupy"
> wrote:
>
>> Neil, Jack up your coach and remove the wheels and tires. I surmise here
>> that you have the rear/rear calipers with parking brakes. I have found
>> that
>> if the short lug protruding from the inside brake pad is not indexed with
>> the caliper piston that the pad will not sit squarely onto the piston, and
>> there will be way too much space between the components. That pad material
>> should ride in slight contact with the rotor when they are broken in, and
>> there should also be no visible space between the caliper piston and the
>> backing plate on the pad. Same on all disc/rotors. If you broke the
>> retaining clip off the back of the pad and left anything sticking up in
>> the
>> middle of the pad where the rivet is, the pad should be removed and the
>> rivet head ground down. Also you need to pre adjust the parking brake
>> ratcheting mechanism to eliminate all the space. If you have clearance
>> where I have just described, you will use up available pedal travel taking
>> up that clearance before any pressure can build up in the system. Low
>> pedal, and poor stopping is the result.
>> Jim Hupy
>> Salem, Oregon
>> 78 GMC ROYALE 403
>> On Jul 12, 2015 5:20 PM, "Neil Fonville" wrote:
>>
>>> I'm back to working on my brake project and just not getting it done.
>>> Still have soft pedal and it's takes way too much distance to stop.
>>> It's
>>> far worse from where is started with 2 Disc and 4 Drums that were not
>>> working good.
>>>
>>> Here is rehash of what steps I have taken and maybe someone can help get
>>> me back on track. I'm still amazed I can't find a mechanic/shop in the
>>> Dallas area that could help me with my projects.
>>>
>>> First I installed the Manny rear disc brake kit. Install was straight
>>> forward.
>>> Bleed the system with the standard 2 man pump and release fluid method.
>>> Never felt right and the vehicle was not even remotely drivable.
>>> Replaced proportion valve with Disc/Disc model.
>>> Removed OEM MC and replaced MC with new one from O'rilly. Used the P30
>>> (PN
>>> NMC1668).
>>> Did not bench bleed. Bleed with 2 man pump and release fluid. Still
>>> pedal too soft and not drivable. Removed MC and put on bench and found
>>> front chamber not pushing fluid.
>>> Replaced with another new MC from O'rilly same part number. Pedal
>>> pumped
>>> up tighter but it leaked between the fluid reservoir and cast metal
>>> piston. Still not drivable.
>>> Replaced MC with new one from Autozone (PN NM1641 ). Purchased the Hupy
>>> bleeder. Bleed according to his directions which is RR moving to LF.
>>> Removed lots of air and pumped about 1/2 gallon of fluid through the
>>> system. Still not drivable, pedal too soft and vehicle does not stop.
>>> From 30 to zero takes about 1/4 mile.
>>>
>>> So how do I go about troubleshooting the individual components? How do
>>> I
>>> test hydraulic pressure?
>>>
>>> I'm hoping for someone to give me a systematic approach to resolve this
>>> and get this working.
>>>
>>> Yes, I have spoke with Manny and I really don't think any of the
>>> calipers
>>> are defective.
>>>
>>> Thanks Neil Fonville
>>> 1975 GMC II
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>>
>> _______________________________________________
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>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Disc brake project still in failure mode [message #282000 is a reply to message #281955] |
Mon, 13 July 2015 11:33 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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Senior Member |
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Neil Fonville wrote on Sun, 12 July 2015 19:19...not drivable, pedal too soft and vehicle does not stop. From 30 to zero takes about 1/4 mile.
So how do I go about troubleshooting the individual components? How do I test hydraulic pressure?
I'm hoping for someone to give me a systematic approach to resolve this and get this working.
Yes, I have spoke with Manny and I really don't think any of the calipers are defective.
Thanks Neil Fonville
1975 GMC II I hold off on answering when I think the answers you will get from others will be more helpful. Not working on this thread so let me say this: It will stop better than that with the fronts only. So you got a master cylinder problem or air in the lines/calipers, even the fronts.
So get the fronts working. You don't have to rotate the calipers to get the bleeder at the top of the bubble like you do the rears. You should keep the push rod on the combination valve pushed in when bleeding the fronts.
I say again, get the fronts working and we will come back to the rears after a positive report on the fronts. Note that the combination valve will reduce the fluid pressure to the fronts for anything but full application of pressure at the pedal. That is supposedly to give the shoes time to move out and start engaging the rears before the front disks engage, preserving stopping stability.
The Maintenance Manual has the systematic approach, but that is for OEM configurations. Yours is not stock, but the procedures should prove helpful. It also discusses the function of the combination valve, so read that. The pressure delay function of the combination valve is not required on a 6 disk system.
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| Re: [GMCnet] Disc brake project still in failure mode [message #282136 is a reply to message #281991] |
Tue, 14 July 2015 22:24 |
Neil Fonville
Messages: 68
Registered: May 2014
Karma: 0
|
Member |
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Went back at it today without much success. Removed the MC and made
certain it was bench bleed. No air bubbles when pushing the plunger and
fluid flowed in solid streams. I plugged the rear at the MC and the front
brakes worked OK. Not great but not too bad. Pedal was solid. Attached
rear and bleed with Hupy bleeder. Brake pedal was soft and no braking
action occurred until the pedal was 2/3 the way down. Drivable but not
real safe. Checked to make sure pads were seated on rear rotors and they
were. It did not take much pedal movement to stop the wheel moving when
jacked up and turned by hand. Really at a loss here.
Is there anyone that can help find someone in the DFW area to come help
me? I¹m pretty much over my head now and about done. About ready to list
it for sale and walk away. Lots of nice folks with these and have
provided some help but I just don¹t have the time or energy to deal with a
storage queen. Already missed one trip due to this project and now
canceling another. I took a working coach with OK brakes and now have a
vehicle that is not safe enough to be on congested roads.
Thanks,
Neil Fonville
Allen TX
75 GMC II
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1975 GMC II
Allen, TX
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| Re: [GMCnet] Disc brake project still in failure mode [message #282140 is a reply to message #282136] |
Tue, 14 July 2015 22:58 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Neil,
Are you still using the stock push rod between the brake booster and the MC or have you made a longer one? If you have the wrong length you can have these exact issues.
Look at all the photos to build your own.
http://www.gmcmhphotos.com/photos/master-cylinder-pushrod-gauge/p47330-an-easy-to-make-gauge-for-determining-pushrod-length.html
JR Wright
GMC Great Laker MHC
GMC Eastern States
GMCGL Tech Editor
GMCMHI
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan
> On Jul 14, 2015, at 11:24 PM, Neil Fonville wrote:
>
> Went back at it today without much success. Removed the MC and made
> certain it was bench bleed. No air bubbles when pushing the plunger and
> fluid flowed in solid streams. I plugged the rear at the MC and the front
> brakes worked OK. Not great but not too bad. Pedal was solid. Attached
> rear and bleed with Hupy bleeder. Brake pedal was soft and no braking
> action occurred until the pedal was 2/3 the way down. Drivable but not
> real safe. Checked to make sure pads were seated on rear rotors and they
> were. It did not take much pedal movement to stop the wheel moving when
> jacked up and turned by hand. Really at a loss here.
>
> Is there anyone that can help find someone in the DFW area to come help
> me? I¹m pretty much over my head now and about done. About ready to list
> it for sale and walk away. Lots of nice folks with these and have
> provided some help but I just don¹t have the time or energy to deal with a
> storage queen. Already missed one trip due to this project and now
> canceling another. I took a working coach with OK brakes and now have a
> vehicle that is not safe enough to be on congested roads.
>
> Thanks,
> Neil Fonville
> Allen TX
> 75 GMC II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] Disc brake project still in failure mode [message #282148 is a reply to message #282140] |
Wed, 15 July 2015 06:23 |
Neil Fonville
Messages: 68
Registered: May 2014
Karma: 0
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Member |
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I have not lengthen the push rod at this point. I feel the .010 gap when
beginning to push the pedal. I guess I’m clueless on the braking system
because I don’t understand how .010 gap can lead to 2/3 of the pedal
stroke before braking action occurs? Or the pedal being soft?
I’m very frustrated at this point and must find some on hands help. I
spent about 20 hours installing the kit. 60 trying to bleed it and get the
MC replaced. Can’t be this hard.
Neil
On 7/14/15, 10:58 PM, "Gmclist on behalf of John Wright"
wrote:
> Neil,
> Are you still using the stock push rod between the brake booster and the
> MC or have you made a longer one? If you have the wrong length you can
> have these exact issues.
>
> Look at all the photos to build your own.
> http://www.gmcmhphotos.com/photos/master-cylinder-pushrod-gauge/p47330-an-
> easy-to-make-gauge-for-determining-pushrod-length.html
>
> JR Wright
> GMC Great Laker MHC
> GMC Eastern States
> GMCGL Tech Editor
> GMCMHI
> 78 GMC Buskirk 30’ Stretch
> 1975 GMC Avion (Under Reconstruction)
> Michigan
>
>> On Jul 14, 2015, at 11:24 PM, Neil Fonville
>> wrote:
>>
>> Went back at it today without much success. Removed the MC and made
>> certain it was bench bleed. No air bubbles when pushing the plunger and
>> fluid flowed in solid streams. I plugged the rear at the MC and the
>> front
>> brakes worked OK. Not great but not too bad. Pedal was solid.
>> Attached
>> rear and bleed with Hupy bleeder. Brake pedal was soft and no braking
>> action occurred until the pedal was 2/3 the way down. Drivable but not
>> real safe. Checked to make sure pads were seated on rear rotors and they
>> were. It did not take much pedal movement to stop the wheel moving when
>> jacked up and turned by hand. Really at a loss here.
>>
>> Is there anyone that can help find someone in the DFW area to come help
>> me? I¹m pretty much over my head now and about done. About ready to
>> list
>> it for sale and walk away. Lots of nice folks with these and have
>> provided some help but I just don¹t have the time or energy to deal
>> with a
>> storage queen. Already missed one trip due to this project and now
>> canceling another. I took a working coach with OK brakes and now have a
>> vehicle that is not safe enough to be on congested roads.
>>
>> Thanks,
>> Neil Fonville
>> Allen TX
>> 75 GMC II
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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_______________________________________________
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1975 GMC II
Allen, TX
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| Re: [GMCnet] Disc brake project still in failure mode [message #282153 is a reply to message #282148] |
Wed, 15 July 2015 08:28 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
|
Senior Member |
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"...can't be this hard." Sorry, but Yes, it can. When I, with the help of
highly experienced GMCers Bobby Moore and JR Slaten, installed Eldorado
rear discs in 2001, we probably pumped 3+ quarts of fluid through the
system before eliminating all the air. Many have encountered worse. I've
used "pump & hold", Vacuum at bleeder, Pressure bleeder, and System vacuum
on various installations. They've all worked, eventually, but not one has
been easy.
First about that 0.100" pushrod clearance (actually, more like 0.120"):
Because of the "pedal ratio" (the length of the pedal arm vs the length of
the bell crank that actually pushes on the booster/master cylinder), which
is somewhere around 6:1, Add the minimum 0.005" clearance the pushrod
should have had before you moved the bracket to the 0.120" and you have
1/8" pushrod clearance MINIMUM. The result is that the pushrod clearance
allows the pedal to go down about 3/4" before you even begin to try to
apply the brakes. And there is some other play in the system, such as the
input clevis on the bellcrank and in the cross-shaft bushings. 3/4" is
probably the minimum pedal play you'll see.
Then, before the brakes begin to apply, there's the "slop" in the brakes
themselves:
1. The calipers are designed so that the rubber seals retract the pistons
a tiny bit via hysteresis. That's intended to keep the brakes from
dragging. I don't think any of us know what that distance is, but remember
that it's present at 6 locations, and is amplified by the hydraulic
advantage of the system. I don't know that number off hand but it's on the
order of 10:1. So, if each caliper moves only 0.005", that's 0.050" at the
MC, multiplied by that 6:1 pedal ratio, giving another 0.300" -- over 1/4"
added to your 3/4", or 1" free play.
2. Then there's disc runout. We'd like the rotor to have NO axial runout
-- but every one of them does. And on old equipment like our GMC's, it can
be quite significant, even when one has installed new discs, as you did
with the Manny Brakes. I've done several of those upgrades and have used a
dial indicator to measure the runout. It has not proven unusual to see
0.010", especially if special care is not taken to clean ALL the rust off
of the hub where the rotor mounts. If you see more than 0.005" runout on
any rotor, it needs correction for optimal brake performance. Remember:
runout causes kick-back of the caliper pistons exactly like in 1.,
preceding.
3. Finally, there's the inevitable axial rotor movement due to wheel
bearing clearance. There shouldn't be much of that at the front wheels,
but the middle and rear wheels WILL have some. Manual X7525 specifies
0.001"-0.005" -- I, and many others prefer the 0.005" or more and it's
likely that most have at least 0.005". That end play is likewise amplified
by the system putting the pedal still lower.
My own brake pedal, even with the newly installed Hydroboost, probably goes
down
1" before achieving any significant braking. I've driven only one GMC
that did better; it also had Hydroboost and had been worked on very
intently by Bob Stone and probably had 1/2"+ play. If you can make a
moderately fast stop with 1/2 pedal, you're probably in pretty good shape.
But you're going to have to fix that push rod to have any chance of getting
there.
JMHO,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc.
www.gmcwipersetc.com
On Wed, Jul 15, 2015 at 7:23 AM, Neil Fonville wrote:
> I have not lengthen the push rod at this point. I feel the .010 gap when
> beginning to push the pedal. I guess I’m clueless on the braking system
> because I don’t understand how .010 gap can lead to 2/3 of the pedal
> stroke before braking action occurs? Or the pedal being soft?
>
> I’m very frustrated at this point and must find some on hands help. I
> spent about 20 hours installing the kit. 60 trying to bleed it and get the
> MC replaced. Can’t be this hard.
>
> Neil
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Disc brake project still in failure mode [message #282157 is a reply to message #282153] |
Wed, 15 July 2015 09:04 |
Neil Fonville
Messages: 68
Registered: May 2014
Karma: 0
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Member |
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Now I really realize I'm in over my head. I only understand parts of this. So let me work on getting the pin extended. How do I remove the metal pin from the black sleeve that is about 1" in diameter that holds the metal pin?
Ken: Thanks for taking the time to write this up. I know it's time consuming.
Neil
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Ken Henderson
Sent: Wednesday, July 15, 2015 8:28 AM
To: GMCNet
Subject: Re: [GMCnet] Disc brake project still in failure mode
"...can't be this hard." Sorry, but Yes, it can. When I, with the help of highly experienced GMCers Bobby Moore and JR Slaten, installed Eldorado rear discs in 2001, we probably pumped 3+ quarts of fluid through the system before eliminating all the air. Many have encountered worse. I've used "pump & hold", Vacuum at bleeder, Pressure bleeder, and System vacuum on various installations. They've all worked, eventually, but not one has been easy.
First about that 0.100" pushrod clearance (actually, more like 0.120"):
Because of the "pedal ratio" (the length of the pedal arm vs the length of the bell crank that actually pushes on the booster/master cylinder), which is somewhere around 6:1, Add the minimum 0.005" clearance the pushrod should have had before you moved the bracket to the 0.120" and you have 1/8" pushrod clearance MINIMUM. The result is that the pushrod clearance allows the pedal to go down about 3/4" before you even begin to try to apply the brakes. And there is some other play in the system, such as the input clevis on the bellcrank and in the cross-shaft bushings. 3/4" is probably the minimum pedal play you'll see.
Then, before the brakes begin to apply, there's the "slop" in the brakes
themselves:
1. The calipers are designed so that the rubber seals retract the pistons a tiny bit via hysteresis. That's intended to keep the brakes from dragging. I don't think any of us know what that distance is, but remember that it's present at 6 locations, and is amplified by the hydraulic advantage of the system. I don't know that number off hand but it's on the order of 10:1. So, if each caliper moves only 0.005", that's 0.050" at the MC, multiplied by that 6:1 pedal ratio, giving another 0.300" -- over 1/4"
added to your 3/4", or 1" free play.
2. Then there's disc runout. We'd like the rotor to have NO axial runout
-- but every one of them does. And on old equipment like our GMC's, it can be quite significant, even when one has installed new discs, as you did with the Manny Brakes. I've done several of those upgrades and have used a dial indicator to measure the runout. It has not proven unusual to see 0.010", especially if special care is not taken to clean ALL the rust off of the hub where the rotor mounts. If you see more than 0.005" runout on any rotor, it needs correction for optimal brake performance. Remember:
runout causes kick-back of the caliper pistons exactly like in 1., preceding.
3. Finally, there's the inevitable axial rotor movement due to wheel bearing clearance. There shouldn't be much of that at the front wheels, but the middle and rear wheels WILL have some. Manual X7525 specifies 0.001"-0.005" -- I, and many others prefer the 0.005" or more and it's likely that most have at least 0.005". That end play is likewise amplified by the system putting the pedal still lower.
My own brake pedal, even with the newly installed Hydroboost, probably goes down 1" before achieving any significant braking. I've driven only one GMC that did better; it also had Hydroboost and had been worked on very intently by Bob Stone and probably had 1/2"+ play. If you can make a moderately fast stop with 1/2 pedal, you're probably in pretty good shape.
But you're going to have to fix that push rod to have any chance of getting there.
JMHO,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL, Manny Brakes & 1-Ton, etc., etc.
www.gmcwipersetc.com
On Wed, Jul 15, 2015 at 7:23 AM, Neil Fonville wrote:
> I have not lengthen the push rod at this point. I feel the .010 gap
> when beginning to push the pedal. I guess I’m clueless on the braking
> system because I don’t understand how .010 gap can lead to 2/3 of the
> pedal stroke before braking action occurs? Or the pedal being soft?
>
> I’m very frustrated at this point and must find some on hands help. I
> spent about 20 hours installing the kit. 60 trying to bleed it and get
> the MC replaced. Can’t be this hard.
>
> Neil
>
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Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
_______________________________________________
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1975 GMC II
Allen, TX
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