Home » Public Forums » GMCnet » [GMCnet] Disc brake project still in failure mode
| [GMCnet] Disc brake project still in failure mode [message #282566] |
Sun, 19 July 2015 23:06  |
glwgmc
Messages: 1014
Registered: June 2004
Karma: 10
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Senior Member |
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Last post from me on this topic……
I think I remimber that you said you purchased the distribution valve used and wondered if it was the right one. With all the issues you habve described, my suggestion is to buy a new disk/disk 4 unit from one of the Jims and eliminate that as an issue FIRST. With that replaced with the right one, then hook up the lines correctly and bleed the brakes using a pressure bleeder. If you need a photo of the correct hookup, I will send you one if you ask. I use a stock MC with the Manny disk/disk system on the Royale with no issue. The pedal is a bit lower and a bit softer than the stock disk/drum/drum set up, but the coach stops well with moderately hard pedal. If that is not your experience, then assume something is wrong with what you have done so start over. The probability that you have a block in the hard lines is close to zero. The likelyhood that you have mush in your soft rubber lines approaches 100% from what you have descirbed. The likelyhood that you have the wrong distribution valve (the 2 variety) from the symptons you describe is close to 100%. The likelyhood that that wrong (2) valve is stuck or gunked up inside is……..
Anyway, not trying to be a smart a**, just thinking through all the help you have received and you still finding the brakes don’t work when many of us have a difference experience suggests to me that what looks right to you may not be.
Jerry
Jerry & Sharon Work
Kerby, OR
glwork@mac.com
http://jerrywork.com
78 Royale
77/94 Clasco
==========
Message: 7
Date: Sun, 19 Jul 2015 16:59:05 -0700
From: James Hupy
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Disc brake project still in failure mode
Message-ID:
Content-Type: text/plain; charset=UTF-8
Comes back to air in the system, compressing, allowing the spool valve to
obstruct the ports, thereby creating a pressure differential. When that
valve has equal pressure applied to both sides, it stays centered allowing
equal but separate fluid streams to go to both front and rear. If your
valve is as crude as others that I have encountered, it's possible that
there is a burr preventing the valve from centering. Just a guess, but one
worth checking out to verify.
Jim Hupy
On Jul 19, 2015 4:49 PM, "Ken Henderson" wrote:
===================
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] Disc brake project still in failure mode [message #282567 is a reply to message #282566] |
Sun, 19 July 2015 23:17  |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Jerry,
My thoughts exactly!
I have a brass disk / drum combination valve from JimB on Double Trouble with 80mm calipers on the front and middle wheels and drums
on the rear and it works perfectly!
Regards,
Rob M.
The Pedantic Mechanic
-----Original Message-----
From: Gerald Work
Last post from me on this topic..
I think I remimber that you said you purchased the distribution valve used and wondered if it was the right one. With all the
issues you habve described, my suggestion is to buy a new disk/disk 4 unit from one of the Jims and eliminate that as an issue
FIRST. With that replaced with the right one, then hook up the lines correctly and bleed the brakes using a pressure bleeder. If
you need a photo of the correct hookup, I will send you one if you ask. I use a stock MC with the Manny disk/disk system on the
Royale with no issue. The pedal is a bit lower and a bit softer than the stock disk/drum/drum set up, but the coach stops well with
moderately hard pedal. If that is not your experience, then assume something is wrong with what you have done so start over. The
probability that you have a block in the hard lines is close to zero. The likelyhood that you have mush in your soft rubber lines
approaches 100% from what you have descirbed. The likelyhood that you have the wrong distribution valve (the 2 variety) from the
symptons you describe is close to 100%. The likelyhood that that wrong (2) valve is stuck or gunked up inside is....
Anyway, not trying to be a smart a**, just thinking through all the help you have received and you still finding the brakes don't
work when many of us have a difference experience suggests to me that what looks right to you may not be.
Jerry
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Disc brake project still in failure mode [message #282572 is a reply to message #282567] |
Mon, 20 July 2015 03:59 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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YES, YES ,YES
many of us are livin the dream,now, with our GMCs,.
- have been for almost 20 years
- have 2 or more GMCs ( I am sorry to say I have 3🙀)
- have none of these problems
Do the work
Follow the examples
And, drive,drive,drive
Just saying
On Sunday, July 19, 2015, Robert Mueller wrote:
> Jerry,
>
> My thoughts exactly!
>
> I have a brass disk / drum combination valve from JimB on Double Trouble
> with 80mm calipers on the front and middle wheels and drums
> on the rear and it works perfectly!
>
> Regards,
> Rob M.
> The Pedantic Mechanic
>
> -----Original Message-----
> From: Gerald Work
>
> Last post from me on this topic..
>
> I think I remimber that you said you purchased the distribution valve used
> and wondered if it was the right one. With all the
> issues you habve described, my suggestion is to buy a new disk/disk 4 unit
> from one of the Jims and eliminate that as an issue
> FIRST. With that replaced with the right one, then hook up the lines
> correctly and bleed the brakes using a pressure bleeder. If
> you need a photo of the correct hookup, I will send you one if you ask. I
> use a stock MC with the Manny disk/disk system on the
> Royale with no issue. The pedal is a bit lower and a bit softer than the
> stock disk/drum/drum set up, but the coach stops well with
> moderately hard pedal. If that is not your experience, then assume
> something is wrong with what you have done so start over. The
> probability that you have a block in the hard lines is close to zero. The
> likelyhood that you have mush in your soft rubber lines
> approaches 100% from what you have descirbed. The likelyhood that you
> have the wrong distribution valve (the 2 variety) from the
> symptons you describe is close to 100%. The likelyhood that that wrong
> (2) valve is stuck or gunked up inside is....
>
> Anyway, not trying to be a smart a**, just thinking through all the help
> you have received and you still finding the brakes don't
> work when many of us have a difference experience suggests to me that what
> looks right to you may not be.
>
> Jerry
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: [GMCnet] Disc brake project still in failure mode [message #283087 is a reply to message #282572] |
Sat, 25 July 2015 07:07 |
Neil Fonville
Messages: 68
Registered: May 2014
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Member |
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Update: So I installed the new combination valve using the screw in lock
tool while bleeding. The screw in lock tool keeps the internal pin from
moving and replaces the brake light connection during installation. Used
the Hupy bleeder and bleed the system by farther to closest to MC. Very
much improved. The coach is drivable and braking action is pretty good
but not great. I will drive it some this weekend to see if it improves
with settling in of the brake pads.
I have a few questions:
I get 800 psi at the MC but only 700 at the RR caliper. Does that mean I
still have a bit of air or tiny leak?
Since the MC is only pushing 800 psi. Would that be my max throughout
the system? Can anything be done to improve that?
The pedal has to be much farther in the stroke for the braking action to
occur. Did I not get the pin length long enough or incorrect?
Thanks for all the input during this.
Neil
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1975 GMC II
Allen, TX
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| Re: [GMCnet] Disc brake project still in failure mode [message #283111 is a reply to message #283087] |
Sat, 25 July 2015 12:14 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Neil,
Is that pressure differential read using the same gauge in both locations?
If so, how do you apply the same pedal pressure after moving the gauge?
Don't count on much more than that 800 psi without a Powermaster,
Hydroboost, or other booster.
I don't think you ever described how you determined the length of your new
MC pushrod, so we can't have any idea whether it's likely to be correct.
However, my experience is that you're not going to get a "high" pedal on a
GMC.
Ken H.
On Sat, Jul 25, 2015 at 8:07 AM, Neil Fonville wrote:
> ...
>
> I have a few questions:
>
> I get 800 psi at the MC but only 700 at the RR caliper. Does that mean I
> still have a bit of air or tiny leak?
>
> Since the MC is only pushing 800 psi. Would that be my max throughout
> the system? Can anything be done to improve that?
>
> The pedal has to be much farther in the stroke for the braking action to
> occur. Did I not get the pin length long enough or incorrect?
>
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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 #283118 is a reply to message #283111] |
Sat, 25 July 2015 13:10 |
Neil Fonville
Messages: 68
Registered: May 2014
Karma: 0
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Member |
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I’m using the same gauge installed in different places. First was direct
on the MC port. Second was the rear output of the combination valve. Got
800 on both of those. Then moved to the RR caliper and got 700. I press
the pedal as hard as I can with engine running and hold for about 30
seconds to stabilize then take a reading. On the MC and combiner output
it jumps straight to 800 and never fluctuated. The RR will fluctuate a
small amount then hit 700 and stay while holding. The pedal does not
touch the firewall but is really close to a full stroke.
I only have the vacuum booster so 700-800 psi would be considered ok?
To measure the pushrod, I took an old radio antenna and extended it too
long and mounted the mc. The rod collapsed to the length. I found it to
be about 3mm longer than the existing rod.
I’m going to drive it tomorrow and get a real feel for what I have. Much,
much better than were I was last weekend for sure.
Neil
On 7/25/15, 12:14 PM, "Gmclist on behalf of Ken Henderson"
wrote:
> Neil,
>
> Is that pressure differential read using the same gauge in both locations?
> If so, how do you apply the same pedal pressure after moving the gauge?
>
> Don't count on much more than that 800 psi without a Powermaster,
> Hydroboost, or other booster.
>
> I don't think you ever described how you determined the length of your new
> MC pushrod, so we can't have any idea whether it's likely to be correct.
> However, my experience is that you're not going to get a "high" pedal on a
> GMC.
>
> Ken H.
>
>
> On Sat, Jul 25, 2015 at 8:07 AM, Neil Fonville
> wrote:
>
>> ...
>>
>> I have a few questions:
>>
>> I get 800 psi at the MC but only 700 at the RR caliper. Does that mean
>> I
>> still have a bit of air or tiny leak?
>>
>> Since the MC is only pushing 800 psi. Would that be my max throughout
>> the system? Can anything be done to improve that?
>>
>> The pedal has to be much farther in the stroke for the braking action to
>> occur. Did I not get the pin length long enough or incorrect?
>>
> _______________________________________________
> GMCnet mailing list
> 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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| Re: [GMCnet] Disc brake project still in failure mode [message #283134 is a reply to message #283118] |
Sat, 25 July 2015 18:01 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Neil,
Without knowing for sure, I suspect you're putting the gauge into the
subject connection directly, without a tee. Recognize that if that's true,
you are not measuring the effects of residual trapped air until you get to
the caliper (bleeder, I assume). Recognizing that, and the fact that your
foot is not really calibrated, I'm not surprised that you "read" a
different value at the caliper than at the other locations. I wouldn't
worry about it.
The most pressure I've ever seen in a vacuum boosted GMC brake system, with
a 1-1/4" ID MC, is 1125 psi. With your P30 MC, the piston area is 13%
larger than with a 1-1/4" MC, so you will achieve 13% less line pressure.
By that logic, my max 1125 would be 975 -- not that much above your 800.
The biggest error in your antenna gauge is the fact that it MC end does not
match the profile of the push rod. With that taken into account, your 3 mm
clearance may be as much at 0.125" -- far above the 0.005"-0.010" you need
-- there's some of your free play in the pedal. Yesterday I measured the
pedal-bellcrank ratio on my spare brake pedal assembly -- it's right at
3:1. That means if you have 1/8" of push rod clearance, your pedal can't
do anything to the MC until it's moved 3/8". There's probably another 1/8"
in the MC before the piston reaches and blocks the compensation ports, so
now the pedal's got to move 3/4" to do ANYTHING toward braking. See how it
adds up on you? :-)
After you've got some miles on those pads, try again to get that last
little bit of air out of the calipers.
JWID,
Ken H.
On Sat, Jul 25, 2015 at 2:10 PM, Neil Fonville wrote:
> I’m using the same gauge installed in different places. First was direct
> on the MC port. Second was the rear output of the combination valve. Got
> 800 on both of those. Then moved to the RR caliper and got 700. I press
> the pedal as hard as I can with engine running and hold for about 30
> seconds to stabilize then take a reading. On the MC and combiner output
> it jumps straight to 800 and never fluctuated. The RR will fluctuate a
> small amount then hit 700 and stay while holding. The pedal does not
> touch the firewall but is really close to a full stroke.
>
> I only have the vacuum booster so 700-800 psi would be considered ok?
>
> To measure the pushrod, I took an old radio antenna and extended it too
> long and mounted the mc. The rod collapsed to the length. I found it to
> be about 3mm longer than the existing rod.
>
> I’m going to drive it tomorrow and get a real feel for what I have. Much,
> much better than were I was last weekend for sure.
>
> 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 #283136 is a reply to message #283134] |
Sat, 25 July 2015 18:20 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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One other observation. Don't be terribly concerned about 800 psi. You will
achieve loss of traction with the road surface (big variable here)
somewhere in the neighborhood of 400 psi. Smooth roads a bit less, coarse
ones a bit more. So, if you have the capability of 2500 psi or 800 psi, it
is kind of a moot point. Far more important to have good "pedal feel". That
comes from having something happening, as far as resistance to foot effort,
as early as possible during pedal application. That's where eliminating all
the slack in the mechanism as well as all air from the system is very
importance. Trust me on this last part. AFTER YOU BREAK IN THOSE PADS AND
ROTORS, YOU WILL NOTICE A VERY LARGE IMPROVEMENT IN FEEL AND STOPPING
ABILITY.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Jul 25, 2015 4:01 PM, "Ken Henderson" wrote:
> Neil,
>
> Without knowing for sure, I suspect you're putting the gauge into the
> subject connection directly, without a tee. Recognize that if that's true,
> you are not measuring the effects of residual trapped air until you get to
> the caliper (bleeder, I assume). Recognizing that, and the fact that your
> foot is not really calibrated, I'm not surprised that you "read" a
> different value at the caliper than at the other locations. I wouldn't
> worry about it.
>
> The most pressure I've ever seen in a vacuum boosted GMC brake system, with
> a 1-1/4" ID MC, is 1125 psi. With your P30 MC, the piston area is 13%
> larger than with a 1-1/4" MC, so you will achieve 13% less line pressure.
> By that logic, my max 1125 would be 975 -- not that much above your 800.
>
> The biggest error in your antenna gauge is the fact that it MC end does not
> match the profile of the push rod. With that taken into account, your 3 mm
> clearance may be as much at 0.125" -- far above the 0.005"-0.010" you need
> -- there's some of your free play in the pedal. Yesterday I measured the
> pedal-bellcrank ratio on my spare brake pedal assembly -- it's right at
> 3:1. That means if you have 1/8" of push rod clearance, your pedal can't
> do anything to the MC until it's moved 3/8". There's probably another 1/8"
> in the MC before the piston reaches and blocks the compensation ports, so
> now the pedal's got to move 3/4" to do ANYTHING toward braking. See how it
> adds up on you? :-)
>
> After you've got some miles on those pads, try again to get that last
> little bit of air out of the calipers.
>
> JWID,
>
> Ken H.
>
>
> On Sat, Jul 25, 2015 at 2:10 PM, Neil Fonville
> wrote:
>
>> I’m using the same gauge installed in different places. First was direct
>> on the MC port. Second was the rear output of the combination valve.
> Got
>> 800 on both of those. Then moved to the RR caliper and got 700. I
> press
>> the pedal as hard as I can with engine running and hold for about 30
>> seconds to stabilize then take a reading. On the MC and combiner output
>> it jumps straight to 800 and never fluctuated. The RR will fluctuate a
>> small amount then hit 700 and stay while holding. The pedal does not
>> touch the firewall but is really close to a full stroke.
>>
>> I only have the vacuum booster so 700-800 psi would be considered ok?
>>
>> To measure the pushrod, I took an old radio antenna and extended it too
>> long and mounted the mc. The rod collapsed to the length. I found it to
>> be about 3mm longer than the existing rod.
>>
>> I’m going to drive it tomorrow and get a real feel for what I have.
> Much,
>> much better than were I was last weekend for sure.
>>
>> Neil
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: [GMCnet] Disc brake project still in failure mode [message #283145 is a reply to message #283136] |
Sat, 25 July 2015 19:49 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Neal,
your not tilting the caliper at 12 O clock position to get all the air out.
We have installed over 25 of these kits and I have found that you must do
it , otherwise your still going to have the problem.
Also we know that the caliper your using is the small one and your not
going to get the performance your seeking.
We learned a lit when we developed the first Reaction Arm System with Chuck
Augler few years back and in the past with Al Branscom and Tom Pryor.These
men know Calipers and what each is capable of. Not like some others.
We spent numerous weekends testing and recording data on the rear disc and
know that we spent little time with rod length and distribution valves as
we found it was all not that critical.
I know Jeff Sirum is another one that has install many disc units and he
will tell you the same.
I hate to see you put in hours when we can help you more as we do these
frequently so we tend to know more than those that has done few.
On Sat, Jul 25, 2015 at 4:20 PM, James Hupy wrote:
> One other observation. Don't be terribly concerned about 800 psi. You will
> achieve loss of traction with the road surface (big variable here)
> somewhere in the neighborhood of 400 psi. Smooth roads a bit less, coarse
> ones a bit more. So, if you have the capability of 2500 psi or 800 psi, it
> is kind of a moot point. Far more important to have good "pedal feel". That
> comes from having something happening, as far as resistance to foot effort,
> as early as possible during pedal application. That's where eliminating all
> the slack in the mechanism as well as all air from the system is very
> importance. Trust me on this last part. AFTER YOU BREAK IN THOSE PADS AND
> ROTORS, YOU WILL NOTICE A VERY LARGE IMPROVEMENT IN FEEL AND STOPPING
> ABILITY.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
> On Jul 25, 2015 4:01 PM, "Ken Henderson" wrote:
>
>> Neil,
>>
>> Without knowing for sure, I suspect you're putting the gauge into the
>> subject connection directly, without a tee. Recognize that if that's
> true,
>> you are not measuring the effects of residual trapped air until you get
> to
>> the caliper (bleeder, I assume). Recognizing that, and the fact that
> your
>> foot is not really calibrated, I'm not surprised that you "read" a
>> different value at the caliper than at the other locations. I wouldn't
>> worry about it.
>>
>> The most pressure I've ever seen in a vacuum boosted GMC brake system,
> with
>> a 1-1/4" ID MC, is 1125 psi. With your P30 MC, the piston area is 13%
>> larger than with a 1-1/4" MC, so you will achieve 13% less line pressure.
>> By that logic, my max 1125 would be 975 -- not that much above your 800.
>>
>> The biggest error in your antenna gauge is the fact that it MC end does
> not
>> match the profile of the push rod. With that taken into account, your 3
> mm
>> clearance may be as much at 0.125" -- far above the 0.005"-0.010" you
> need
>> -- there's some of your free play in the pedal. Yesterday I measured the
>> pedal-bellcrank ratio on my spare brake pedal assembly -- it's right at
>> 3:1. That means if you have 1/8" of push rod clearance, your pedal can't
>> do anything to the MC until it's moved 3/8". There's probably another
> 1/8"
>> in the MC before the piston reaches and blocks the compensation ports, so
>> now the pedal's got to move 3/4" to do ANYTHING toward braking. See how
> it
>> adds up on you? :-)
>>
>> After you've got some miles on those pads, try again to get that last
>> little bit of air out of the calipers.
>>
>> JWID,
>>
>> Ken H.
>>
>>
>> On Sat, Jul 25, 2015 at 2:10 PM, Neil Fonville
>> wrote:
>>
>>> I’m using the same gauge installed in different places. First was
> direct
>>> on the MC port. Second was the rear output of the combination valve.
>> Got
>>> 800 on both of those. Then moved to the RR caliper and got 700. I
>> press
>>> the pedal as hard as I can with engine running and hold for about 30
>>> seconds to stabilize then take a reading. On the MC and combiner
> output
>>> it jumps straight to 800 and never fluctuated. The RR will fluctuate a
>>> small amount then hit 700 and stay while holding. The pedal does not
>>> touch the firewall but is really close to a full stroke.
>>>
>>> I only have the vacuum booster so 700-800 psi would be considered ok?
>>>
>>> To measure the pushrod, I took an old radio antenna and extended it too
>>> long and mounted the mc. The rod collapsed to the length. I found it
> to
>>> be about 3mm longer than the existing rod.
>>>
>>> I’m going to drive it tomorrow and get a real feel for what I have.
>> Much,
>>> much better than were I was last weekend for sure.
>>>
>>> Neil
>>>
>> _______________________________________________
>> 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:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] Disc brake project still in failure mode [message #283146 is a reply to message #283134] |
Sat, 25 July 2015 19:58 |
A Hamilto
Messages: 4508
Registered: April 2011
Karma: 39
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Senior Member |
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Ken Henderson wrote on Sat, 25 July 2015 18:01Neil,
Without knowing for sure, I suspect you're putting the gauge into the subject connection directly, without a tee. Recognize that if that's true, you are not measuring the effects of residual trapped air until you get to the caliper (bleeder, I assume). Recognizing that, and the fact that your foot is not really calibrated, I'm not surprised that you "read" a different value at the caliper than at the other locations. I wouldn't worry about it. ... He might drive it that way for tens of thousands of miles, but it would bother me until I figured out where it was losing 100 pounds of pressure.
I will say it again. An unobstructed closed pipe will be at the same pressure everywhere in it.
I agree that you need to get all the slack out of the pedal linkage/rod that you can. Nothing costs me confidence more than a brake pedal that is almost at he floor when I am trying to stop.
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| Re: [GMCnet] Disc brake project still in failure mode [message #283149 is a reply to message #283134] |
Sat, 25 July 2015 20:30 |
Neil Fonville
Messages: 68
Registered: May 2014
Karma: 0
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Member |
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Ken: You are right on. It takes about 3/4² to 1² of pedal for any braking
to occur. Good news is I can work on that pin without opening the system.
I have enough room to unbolt and move the MC out of the way if I need to
increase the length a bit.
I just put the gauge in the bleeder port of the caliper. Would the air
tend to move to the caliper over time?
I must say that Jim Hupy¹s bleeder was worth every penny and then some.
Thanks everyone and I will report back after driving a few hundred miles.
Neil
On 7/25/15, 6:01 PM, "Gmclist on behalf of Ken Henderson"
wrote:
> Neil,
>
> Without knowing for sure, I suspect you're putting the gauge into the
> subject connection directly, without a tee. Recognize that if that's
> true,
> you are not measuring the effects of residual trapped air until you get to
> the caliper (bleeder, I assume). Recognizing that, and the fact that your
> foot is not really calibrated, I'm not surprised that you "read" a
> different value at the caliper than at the other locations. I wouldn't
> worry about it.
>
> The most pressure I've ever seen in a vacuum boosted GMC brake system,
> with
> a 1-1/4" ID MC, is 1125 psi. With your P30 MC, the piston area is 13%
> larger than with a 1-1/4" MC, so you will achieve 13% less line pressure.
> By that logic, my max 1125 would be 975 -- not that much above your 800.
>
> The biggest error in your antenna gauge is the fact that it MC end does
> not
> match the profile of the push rod. With that taken into account, your 3
> mm
> clearance may be as much at 0.125" -- far above the 0.005"-0.010" you need
> -- there's some of your free play in the pedal. Yesterday I measured the
> pedal-bellcrank ratio on my spare brake pedal assembly -- it's right at
> 3:1. That means if you have 1/8" of push rod clearance, your pedal can't
> do anything to the MC until it's moved 3/8". There's probably another
> 1/8"
> in the MC before the piston reaches and blocks the compensation ports, so
> now the pedal's got to move 3/4" to do ANYTHING toward braking. See how
> it
> adds up on you? :-)
>
> After you've got some miles on those pads, try again to get that last
> little bit of air out of the calipers.
>
> JWID,
>
> Ken H.
>
>
> On Sat, Jul 25, 2015 at 2:10 PM, Neil Fonville
> wrote:
>
>> I¹m using the same gauge installed in different places. First was
>> direct
>> on the MC port. Second was the rear output of the combination valve.
>> Got
>> 800 on both of those. Then moved to the RR caliper and got 700. I
>> press
>> the pedal as hard as I can with engine running and hold for about 30
>> seconds to stabilize then take a reading. On the MC and combiner output
>> it jumps straight to 800 and never fluctuated. The RR will fluctuate a
>> small amount then hit 700 and stay while holding. The pedal does not
>> touch the firewall but is really close to a full stroke.
>>
>> I only have the vacuum booster so 700-800 psi would be considered ok?
>>
>> To measure the pushrod, I took an old radio antenna and extended it too
>> long and mounted the mc. The rod collapsed to the length. I found it to
>> be about 3mm longer than the existing rod.
>>
>> I¹m going to drive it tomorrow and get a real feel for what I have.
>> Much,
>> much better than were I was last weekend for sure.
>>
>> Neil
>>
> _______________________________________________
> GMCnet mailing list
> 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 #283150 is a reply to message #283145] |
Sat, 25 July 2015 20:34 |
Neil Fonville
Messages: 68
Registered: May 2014
Karma: 0
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Member |
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Thanks Jim for the info. We did remove the caliper and got the bleeder at
12 o¹clock. That made a big difference. Until we did that we were not
having much success.
Neil
On 7/25/15, 7:49 PM, "Gmclist on behalf of Jim Kanomata"
wrote:
> Neal,
> your not tilting the caliper at 12 O clock position to get all the air
> out.
> We have installed over 25 of these kits and I have found that you must do
> it , otherwise your still going to have the problem.
> Also we know that the caliper your using is the small one and your not
> going to get the performance your seeking.
> We learned a lit when we developed the first Reaction Arm System with
> Chuck
> Augler few years back and in the past with Al Branscom and Tom Pryor.These
> men know Calipers and what each is capable of. Not like some others.
> We spent numerous weekends testing and recording data on the rear disc and
> know that we spent little time with rod length and distribution valves as
> we found it was all not that critical.
> I know Jeff Sirum is another one that has install many disc units and he
> will tell you the same.
> I hate to see you put in hours when we can help you more as we do these
> frequently so we tend to know more than those that has done few.
>
>
> On Sat, Jul 25, 2015 at 4:20 PM, James Hupy wrote:
>
>> One other observation. Don't be terribly concerned about 800 psi. You
>> will
>> achieve loss of traction with the road surface (big variable here)
>> somewhere in the neighborhood of 400 psi. Smooth roads a bit less,
>> coarse
>> ones a bit more. So, if you have the capability of 2500 psi or 800 psi,
>> it
>> is kind of a moot point. Far more important to have good "pedal feel".
>> That
>> comes from having something happening, as far as resistance to foot
>> effort,
>> as early as possible during pedal application. That's where eliminating
>> all
>> the slack in the mechanism as well as all air from the system is very
>> importance. Trust me on this last part. AFTER YOU BREAK IN THOSE PADS
>> AND
>> ROTORS, YOU WILL NOTICE A VERY LARGE IMPROVEMENT IN FEEL AND STOPPING
>> ABILITY.
>> Jim Hupy
>> Salem, Or
>> 78 GMC ROYALE 403
>> On Jul 25, 2015 4:01 PM, "Ken Henderson" wrote:
>>
>>> Neil,
>>>
>>> Without knowing for sure, I suspect you're putting the gauge into the
>>> subject connection directly, without a tee. Recognize that if that's
>> true,
>>> you are not measuring the effects of residual trapped air until you
>> get
>> to
>>> the caliper (bleeder, I assume). Recognizing that, and the fact that
>> your
>>> foot is not really calibrated, I'm not surprised that you "read" a
>>> different value at the caliper than at the other locations. I
>> wouldn't
>>> worry about it.
>>>
>>> The most pressure I've ever seen in a vacuum boosted GMC brake system,
>> with
>>> a 1-1/4" ID MC, is 1125 psi. With your P30 MC, the piston area is 13%
>>> larger than with a 1-1/4" MC, so you will achieve 13% less line
>> pressure.
>>> By that logic, my max 1125 would be 975 -- not that much above your
>> 800.
>>>
>>> The biggest error in your antenna gauge is the fact that it MC end
>> does
>> not
>>> match the profile of the push rod. With that taken into account,
>> your 3
>> mm
>>> clearance may be as much at 0.125" -- far above the 0.005"-0.010" you
>> need
>>> -- there's some of your free play in the pedal. Yesterday I measured
>> the
>>> pedal-bellcrank ratio on my spare brake pedal assembly -- it's right
>> at
>>> 3:1. That means if you have 1/8" of push rod clearance, your pedal
>> can't
>>> do anything to the MC until it's moved 3/8". There's probably another
>> 1/8"
>>> in the MC before the piston reaches and blocks the compensation
>> ports, so
>>> now the pedal's got to move 3/4" to do ANYTHING toward braking. See
>> how
>> it
>>> adds up on you? :-)
>>>
>>> After you've got some miles on those pads, try again to get that last
>>> little bit of air out of the calipers.
>>>
>>> JWID,
>>>
>>> Ken H.
>>>
>>>
>>> On Sat, Jul 25, 2015 at 2:10 PM, Neil Fonville
>>> wrote:
>>>
>>>> I¹m using the same gauge installed in different places. First was
>> direct
>>>> on the MC port. Second was the rear output of the combination
>> valve.
>>> Got
>>>> 800 on both of those. Then moved to the RR caliper and got 700. I
>>> press
>>>> the pedal as hard as I can with engine running and hold for about 30
>>>> seconds to stabilize then take a reading. On the MC and combiner
>> output
>>>> it jumps straight to 800 and never fluctuated. The RR will
>> fluctuate a
>>>> small amount then hit 700 and stay while holding. The pedal does
>> not
>>>> touch the firewall but is really close to a full stroke.
>>>>
>>>> I only have the vacuum booster so 700-800 psi would be considered
>> ok?
>>>>
>>>> To measure the pushrod, I took an old radio antenna and extended it
>> too
>>>> long and mounted the mc. The rod collapsed to the length. I found
>> it
>> to
>>>> be about 3mm longer than the existing rod.
>>>>
>>>> I¹m going to drive it tomorrow and get a real feel for what I have.
>>> Much,
>>>> much better than were I was last weekend for sure.
>>>>
>>>> Neil
>>>>
>>> _______________________________________________
>>> 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:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
>
> --
> Jim Kanomata
> Applied/GMC, Fremont,CA
> jimk@appliedairfilters.com
> http://www.appliedgmc.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
> 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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| Re: [GMCnet] Disc brake project still in failure mode [message #283152 is a reply to message #283134] |
Sat, 25 July 2015 21:26 |
|
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Ken,
For the life of me I can not understand why air in the system would drop the pressure 100 psi at the caliper. The air would compress
and the pressure should be the same at the M/C, combination valve outlet, and caliper!
As Neil depressed the brake pedal the pressure to the all the rear wheels should be the same.
The 100 psi pressure drop at the RR caliper contradicts Pascal's Principle (as cited by Mark aka "A")
Pascal's Principle; "A change in pressure at any point in an enclosed fluid at rest is transmitted undiminished to all points in the
fluid."
I note below that Neil states; "On the MC and combiner output it jumps straight to 800 and never fluctuated." And "The RR will
fluctuate a small amount then hit 700 and stay while holding."
I can't remember if Neil advised if the replaced the flex hoses to the rear wheels or not but if he didn't I'm going to guess that
the hose to the RR wheel is restricting fluid flow to that caliper and shutting it off at 700 psi. Come to think of it even if he
DID R&R the hoses the new one might be defective.
I'd suggest Neil perform the following testing:
1) Connect the gage to the driver side rear wheel - record the pressure
2) Connect the gage to the driver side middle wheel - record the pressure
3) Connect the gage to the passenger side rear wheel - record the pressure
4) Connect the gage to the passenger middle rear wheel - record the pressure
Regards,
Rob M.
The Pedantic Mechanic
-----Original Message-----
From: Ken Henderson
Neil,
Without knowing for sure, I suspect you're putting the gauge into the subject connection directly, without a tee. Recognize that if
that's true, you are not measuring the effects of residual trapped air until you get to the caliper (bleeder, I assume).
Recognizing that, and the fact that your foot is not really calibrated, I'm not surprised that you "read" a different value at the
caliper than at the other locations. I wouldn't worry about it.
The most pressure I've ever seen in a vacuum boosted GMC brake system, with a 1-1/4" ID MC, is 1125 psi. With your P30 MC, the
piston area is 13% larger than with a 1-1/4" MC, so you will achieve 13% less line pressure. By that logic, my max 1125 would be 975
-- not that much above your 800.
The biggest error in your antenna gauge is the fact that it MC end does not match the profile of the push rod. With that taken into
account, your 3 mm clearance may be as much at 0.125" -- far above the 0.005"-0.010" you need -- there's some of your free play in
the pedal. Yesterday I measured the pedal-bellcrank ratio on my spare brake pedal assembly -- it's right at 3:1. That means if you
have 1/8" of push rod clearance, your pedal can't do anything to the MC until it's moved 3/8". There's probably another 1/8" in the
MC before the piston reaches and blocks the compensation ports, so now the pedal's got to move 3/4" to do ANYTHING toward braking.
See how it adds up on you? :-)
After you've got some miles on those pads, try again to get that last little bit of air out of the calipers.
JWID,
Ken H.
On Sat, Jul 25, 2015 at 2:10 PM, Neil Fonville wrote:
I'm using the same gauge installed in different places. First was direct on the MC port. Second was the rear output of the
combination valve. Got 800 on both of those. Then moved to the RR caliper and got 700. I press the pedal as hard as I can with
engine running and hold for about 30 seconds to stabilize then take a reading. On the MC and combiner output it jumps straight to
800 and never fluctuated. The RR will fluctuate a small amount then hit 700 and stay while holding. The pedal does not touch the
firewall but is really close to a full stroke.
I only have the vacuum booster so 700-800 psi would be considered ok?
To measure the pushrod, I took an old radio antenna and extended it too long and mounted the mc. The rod collapsed to the length. I
found it to be about 3mm longer than the existing rod.
I'm going to drive it tomorrow and get a real feel for what I have. Much, much better than were I was last weekend for sure.
Neil
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Disc brake project still in failure mode [message #283157 is a reply to message #283152] |
Sat, 25 July 2015 22:51 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
|
Senior Member |
|
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Rob,
Nothing wrong with your logic, but the essential thing to remember is that
he does not have a repeatable input. "Pressing as hard as I can" is NOT a
repeatable input. I don't think the reported 100 psi difference (12.5%) is
signficant.
That's exactly the reason I installed the pneumatic pedal puller 10 years
or so ago -- every time I flip on the compressor, I get almost exactly the
same 140 lbf on the brake pedal. I can press harder than that, but not
consistently.
Ken H.
On Sat, Jul 25, 2015 at 10:26 PM, Robert Mueller
wrote:
> Ken,
>
> For the life of me I can not understand why air in the system would drop
> the pressure 100 psi at the caliper. The air would compress
> and the pressure should be the same at the M/C, combination valve outlet,
> and caliper!
>
> As Neil depressed the brake pedal the pressure to the all the rear wheels
> should be the same.
>
> The 100 psi pressure drop at the RR caliper contradicts Pascal's Principle
> (as cited by Mark aka "A")
>
> Pascal's Principle; "A change in pressure at any point in an enclosed
> fluid at rest is transmitted undiminished to all points in the
> fluid."
>
> I note below that Neil states; "On the MC and combiner output it jumps
> straight to 800 and never fluctuated." And "The RR will
> fluctuate a small amount then hit 700 and stay while holding."
>
> I can't remember if Neil advised if the replaced the flex hoses to the
> rear wheels or not but if he didn't I'm going to guess that
> the hose to the RR wheel is restricting fluid flow to that caliper and
> shutting it off at 700 psi. Come to think of it even if he
> DID R&R the hoses the new one might be defective.
>
> I'd suggest Neil perform the following testing:
>
> 1) Connect the gage to the driver side rear wheel - record the pressure
> 2) Connect the gage to the driver side middle wheel - record the pressure
> 3) Connect the gage to the passenger side rear wheel - record the pressure
> 4) Connect the gage to the passenger middle rear wheel - record the
> pressure
>
> Regards,
> Rob M.
> The Pedantic Mechanic
>
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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 #283175 is a reply to message #283159] |
Sun, 26 July 2015 05:53 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
|
Senior Member |
|
|
I agree. Unfortunately, my pneumatic pedal puller is permanently mounted
beneath the floorboard beneath the brake pedal. :-)
What's your theory of how the closed system pressure can vary
location-to-location under "identical" conditions?
Ken H.
On Sun, Jul 26, 2015 at 12:19 AM, A. wrote:
> ...
>
But there is an indication that he is more consistent than you believe. He
> installs the gauge at the MC and "presses as hard as he can" and gets 800
> PSI. He removes the gauge and installs it at the output of the combination
> valve, "presses as hard as he can" and gets 800 PSI. I have no reason to
> believe that when he removes the gauge from the output of the combination
> valve and puts it at the caliper, and "presses as hard as he can" that he
> should see anything but 800 PSI.
>
> I wish he could borrow your pneumatic pedal puller. Then we'd know who's
> right.
> --
>
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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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