Home » Public Forums » GMCnet » What causes possible for front caliper bind (combo valve?)
| What causes possible for front caliper bind [message #270500] |
Mon, 26 January 2015 22:42  |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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I pulled a front brake a while back, and the driver side pad was burned up/crumbling it had gotten so hot at some point. I put another set on (both sides), but I've been thinking...the caliper did not want to open up to make room for the new pad. I had to open the bleeder valve. I replaced the caliper and hose two years ago when I bought the coach out of sitting/storage. Would a blocked combo valve cause that caliper to stick/resist opening up? It acted like people describe the hoses going bad and functioning as a one way valve, but that hose is pretty new. If something is binding it, that would explain the pad premature wear/overheat as well as the piston unwilling to retract for pad replacement.
I found this walkthrough
http://www.gmcmhphotos.com/photos/deciphering-the-combination-valve/p5314.html
where Ken Henderson makes some changes. I would just be checking for overall condition, not changing the valve. I know the Jim's sell new combo valves, but wondering if that is the right track.
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: [GMCnet] What causes possible for front caliper bind [message #270502 is a reply to message #270500] |
Mon, 26 January 2015 23:43  |
powwerjon
Messages: 849
Registered: March 2013
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Tyler,
I would suggest that the brake hoses on the front have collapsed internally not allowing the front brakes to release. The first tipoff was when you had to open the bleed valve on the caliper. Replace the brake lines and you should see an great improvement. The combo valve is probably NOT your problem. What calipers are you running on the front, stock or upgraded 80MM? Once we know we can point you to the correct part number for the new brake lines.
J.R. Wright
30' Buskirk Stretch
Michigan
On Location in Tucson
> On Jan 26, 2015, at 9:42 PM, Tyler wrote:
>
> I pulled a front brake a while back, and the driver side pad was burned up/crumbling it had gotten so hot at some point. I put another set on (both
> sides), but I've been thinking...the caliper did not want to open up to make room for the new pad. I had to open the bleeder valve. I replaced the
> caliper and hose two years ago when I bought the coach out of sitting/storage. Would a blocked combo valve cause that caliper to stick/resist opening
> up? It acted like people describe the hoses going bad and functioning as a one way valve, but that hose is pretty new. If something is binding it,
> that would explain the pad premature wear/overheat as well as the piston unwilling to retract for pad replacement.
>
> I found this walkthrough
> http://www.gmcmhphotos.com/photos/deciphering-the-combination-valve/p5314.html
> where Ken Henderson makes some changes. I would just be checking for overall condition, not changing the valve. I know the Jim's sell new combo
> valves, but wondering if that is the right track.
>
> --
> 1975 Glenbrook
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| Re: What causes possible for front caliper bind [message #270503 is a reply to message #270500] |
Tue, 27 January 2015 00:24 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
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If only the one side is binding up and opening the bleed valve released it I would have to agree with JR. the 80mm have a banjo fitting rather then a flair fitting at the caliper.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: [GMCnet] What causes possible for front caliper bind [message #270522 is a reply to message #270502] |
Tue, 27 January 2015 07:49 |
Kingsley Coach
Messages: 2691
Registered: March 2009
Location: Nova Scotia Canada
Karma: -34
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Tyler
John is right about the brake line, but you said, "...the driver side pad
was burned up/crumbling it had gotten so hot at some point."
You might want to check the bearings on that side.
If we knew where you lived, someone could lend assistance if you are at a
loss on this topic.
Mike in NS..waiting for the storm !
On Tue, Jan 27, 2015 at 1:43 AM, John Wright wrote:
> Tyler,
> I would suggest that the brake hoses on the front have collapsed
> internally not allowing the front brakes to release. The first tipoff was
> when you had to open the bleed valve on the caliper. Replace the brake
> lines and you should see an great improvement. The combo valve is probably
> NOT your problem. What calipers are you running on the front, stock or
> upgraded 80MM? Once we know we can point you to the correct part number
> for the new brake lines.
>
> J.R. Wright
> 30' Buskirk Stretch
> Michigan
> On Location in Tucson
>
>> On Jan 26, 2015, at 9:42 PM, Tyler wrote:
>>
>> I pulled a front brake a while back, and the driver side pad was burned
> up/crumbling it had gotten so hot at some point. I put another set on (both
>> sides), but I've been thinking...the caliper did not want to open up to
> make room for the new pad. I had to open the bleeder valve. I replaced the
>> caliper and hose two years ago when I bought the coach out of
> sitting/storage. Would a blocked combo valve cause that caliper to
> stick/resist opening
>> up? It acted like people describe the hoses going bad and functioning as
> a one way valve, but that hose is pretty new. If something is binding it,
>> that would explain the pad premature wear/overheat as well as the piston
> unwilling to retract for pad replacement.
>>
>> I found this walkthrough
>>
> http://www.gmcmhphotos.com/photos/deciphering-the-combination-valve/p5314.html
>> where Ken Henderson makes some changes. I would just be checking for
> overall condition, not changing the valve. I know the Jim's sell new combo
>> valves, but wondering if that is the right track.
>>
>> --
>> 1975 Glenbrook
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> _______________________________________________
> GMCnet mailing list
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--
Michael Beaton
1977 Kingsley 26-11
1977 Eleganza II 26-3
Antigonish, NS
Life is too short to hold a grudge; slash some tires and call it even !
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| Re: What causes possible for front caliper bind [message #273788 is a reply to message #270500] |
Mon, 16 March 2015 09:53 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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More info - got into it again this weekend. Found movement in my brake booster between what I will call the front "pan" and the body of the booster. This is a two year old sensitized booster, bought from a longtime GMC vendor who has now aged out of business, so no support available. It had an unusual click even when new, and now I know it is from seating in those tabs every pedal stroke. The MC was replaced at the same time two years ago (as was the front rubber lines, calipers and pads). Attached is a less than perfect video looking at the bottom of the booster. You can sort of see the movement of the whole front in the tabs that look like they rotate to lock in. There is also some sideways flex of the master cylinder relative to the firewall when more pressure is applied.
I am realizing I need a pro with eyes on it to fully verify safety, but I hate to replace everything for a second time in two years, when only one or two parts may be at issue. And, there is the forum benefit of "yea, that happened to me, I did this"...
So,
Could a booster that is not built quite right be leaving too much drag on the front brakes?
Can I just bend the tabs, or wedge it in tight, to remove the click, or should that be sign of a bad build/booster?
How long should the booster hold vacuum after shutting off the engine? I can hear it releasing about 20 seconds after engine is off, which does not seem long enough.
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: What causes possible for front caliper bind [message #273792 is a reply to message #270500] |
Mon, 16 March 2015 10:07 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Just from my past automotive experience...
other then the old hose issue, dragging calipers, almost always related to the caliper itself. I would replace that, I do not think they are super expensive, and they are easy/quick to change out. I personally would replace both calipers to just know that you are good there. i would guess $80 in parts.
I have seen people clean and lube the slides, and do all sorts of cleaning to fix a caliper, only for a temp fix in most cases.
then if problem persists, chase other items.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: [GMCnet] What causes possible for front caliper bind [message #273794 is a reply to message #273788] |
Mon, 16 March 2015 10:03 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Tyler,
That booster needs to be replaced; There should not be movement as seen in the video and it should not hiss when you shut off the
engine.
Is the bracket that supports the master cylinder present?
Regards,
Rob M.
-----Original Message-----
From: Tyler
More info - got into it again this weekend. Found movement in my brake booster between what I will call the front "pan" and the body
of the booster.
This is a two year old sensitized booster, bought from a longtime GMC vendor who has now aged out of business, so no support
available. It had an unusual click even when new, and now I know it is from seating in those tabs every pedal stroke. The MC was
replaced at the same time two years ago (as was the front rubber lines, calipers and pads). Attached is a less than perfect video
looking at the bottom of the booster. You can sort of see the movement of the whole front in the tabs that look like they rotate to
lock in. There is also some sideways flex of the master cylinder relative to the firewall when more pressure is applied.
I am realizing I need a pro with eyes on it to fully verify safety, but I hate to replace everything for a second time in two years,
when only one or two parts may be at issue. And, there is the forum benefit of "yea, that happened to me, I did this"...
So,
Could a booster that is not built quite right be leaving too much drag on the front brakes?
Can I just bend the tabs, or wedge it in tight, to remove the click, or should that be sign of a bad build/booster?
How long should the booster hold vacuum after shutting off the engine? I can hear it releasing about 20 seconds after engine is off,
which does not
seem long enough.
http://www.gmcmhphotos.com/photos/data/6734/MVI_0841.AVI
--
1975 Glenbrook
Raleigh, NC
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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: What causes possible for front caliper bind [message #273811 is a reply to message #273788] |
Mon, 16 March 2015 11:41 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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RESPONSES are INLINE
Tilerpep wrote on Mon, 16 March 2015 10:53More info - got into it again this weekend. Found movement in my brake booster between what I will call the front "pan" and the body of the booster. This is a two year old sensitized booster, bought from a longtime GMC vendor who has now aged out of business, so no support available. It had an unusual click even when new, and now I know it is from seating in those tabs every pedal stroke. The MC was replaced at the same time two years ago (as was the front rubber lines, calipers and pads). Attached is a less than perfect video looking at the bottom of the booster. You can sort of see the movement of the whole front in the tabs that look like they rotate to lock in. There is also some sideways flex of the master cylinder relative to the firewall when more pressure is applied.
I am realizing I need a pro with eyes on it to fully verify safety, but I hate to replace everything for a second time in two years, when only one or two parts may be at issue. And, there is the forum benefit of "yea, that happened to me, I did this"...
So,
Could a booster that is not built quite right be leaving too much drag on the front brakes? UNLIKEY
Can I just bend the tabs, or wedge it in tight, to remove the click, or should that be sign of a bad build/booster? NO
How long should the booster hold vacuum after shutting off the engine? WEEKS
I can hear it releasing about 20 seconds after engine is off, which does not seem long enough. CORRECT
<Video snipped>
Tyler,
If opening the bleeder let the caliper release, then it is not the caliper that is the problem, but it may have gotten so hot that it should be replaced.
I have known boosters to hold a vacuum for weeks. If it leaks like that, it is bad.
If a booster leaking left pressure on the master cylinder, then you would have fried ALL the brakes, not just one.
Because of the way calipers are constructed, it is easy for one to extend to a place where it will stick. Such a caliper could be repaired, but replacement would be advised.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: What causes possible for front caliper bind [message #274427 is a reply to message #270500] |
Fri, 27 March 2015 09:58 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Follow up post:
Dave Lenzi is the man, just saying... he heard me out and directed me to pushrod interaction between booster and MC. The bad news is that the brakes have been slightly dragging for two years!! Arrrgh. When I took the MC off the booster, that alone let the front wheels play/rotate a few inches to the transmission catches. They were stuck enough I could not rotate them by hand. I got my hands on an OEM booster two weeks ago and compared the original booster and the metric one. I had been very careful when I got the metric one, based on all the forum information to check the pushrod. The rods were the same, I could see no difference two years ago. This time I compared the RELATIVE distance from static state to the plane/surface the booster mounts on. 1.5 mm difference. I put washers on the booster mounting studs, reinstalled the MC and voila - on jack stands the wheels turn by hand with brake off, and brakes apply as expected. Drove around town for 15-20 minutes, and coach is quieter, obviously stronger. Fan clutch not engaging because it is not dragging and causing extra work. Sigh.
The "L" bracket that supports MC from the top had worked loose, tightening that helped rigidity.
Progress!
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: [GMCnet] What causes possible for front caliper bind [message #274452 is a reply to message #274427] |
Fri, 27 March 2015 17:08 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Tyler,
I note below that you noted that "I put washers on the booster."
Please advise:
1) Where you put the washers?
2) How many washers you installed?
3) If you put them in between the booster and the master cylinder how big is the gap between those two units now?
4) When you tighten the nuts that hold the master cylinder to the booster are there threads exposed?
5) If yes how many threads are exposed?
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
USA '75 Avion - Double Trouble TZE365V100426
AUS '75 Avion - The Blue Streak TZE365V100428
-----Original Message-----
From: Tyler
Follow up post:
Dave Lenzi is the man, just saying... he heard me out and directed me to pushrod interaction between booster and MC. The bad news is
that the brakes have been slightly dragging for two years!! Arrrgh. When I took the MC off the booster, that alone let the front
wheels play/rotate a few inches to the transmission catches. They were stuck enough I could not rotate them by hand. I got my hands
on an OEM booster two weeks ago and compared the original booster and the metric one. I had been very careful when I got the metric
one, based on all the forum information to check the pushrod. The rods were the same, I could see no difference two years ago. This
time I compared the RELATIVE distance from static state to the plane/surface the booster mounts on. 1.5 mm difference. I put washers
on the booster mounting studs, reinstalled the MC and voila - on jack stands the wheels turn by hand with brake off, and brakes
apply as expected. Drove around town for 15-20 minutes, and coach is quieter, obviously stronger. Fan clutch not engaging because it
is not dragging and causing extra work. Sigh.
The "L" bracket that supports MC from the top had worked loose, tightening that helped rigidity.
Progress!
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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: What causes possible for front caliper bind [message #274490 is a reply to message #270500] |
Sat, 28 March 2015 09:07 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Senior Member |
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I'll clarify that Dave Lenzi did NOT recommend this as a permanent fix...
I put one washer on each bolt between MC and booster, increasing gap just over 1 mm (ish).
The metric booster has much longer MC attachment bolts than OEM, so threads are not a problem.
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: [GMCnet] What causes possible for front caliper bind [message #274514 is a reply to message #274490] |
Sat, 28 March 2015 15:52 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Tyler,
I knew that Dave would not recommend that as a fix for two reasons:
1) the master cylinder "tail" locates the pushrod to booster seal at the bottom of the port in the booster and does not allow it to
move by shimming the master cylinder out any amount will allow that seal to move back and forth in the port.
2) the under hood area in the GMC gets "flooded" when it rains by shimming the master cylinder out 1mm you have now opened a path
for water to get in between the master cylinder and the booster. If there is water in the booster port and the seal moves it will be
possible for the water to be sucked into the booster.
What you need to do is shorten the push rod so that the brakes are not held on. From what you have noted earlier in this thread it
appears that should be about 1mm.
Regards,
Rob M.
The Pedantic Mechanic
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Tyler
Sent: Saturday, March 28, 2015 9:08 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] What causes possible for front caliper bind
I'll clarify that Dave Lenzi did NOT recommend this as a permanent fix...
I put one washer on each bolt between MC and booster, increasing gap just over 1 mm (ish).
The metric booster has much longer MC attachment bolts than OEM, so threads are not a problem.
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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: What causes possible for front caliper bind [message #274665 is a reply to message #274427] |
Tue, 31 March 2015 14:24 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Tilerpep wrote on Fri, 27 March 2015 08:58Follow up post:
Dave Lenzi is the man, just saying... he heard me out and directed me to pushrod interaction between booster and MC. The bad news is that the brakes have been slightly dragging for two years!! Arrrgh. When I took the MC off the booster, that alone let the front wheels play/rotate a few inches to the transmission catches. They were stuck enough I could not rotate them by hand. I got my hands on an OEM booster two weeks ago and compared the original booster and the metric one. I had been very careful when I got the metric one, based on all the forum information to check the pushrod. The rods were the same, I could see no difference two years ago. This time I compared the RELATIVE distance from static state to the plane/surface the booster mounts on. 1.5 mm difference. I put washers on the booster mounting studs, reinstalled the MC and voila - on jack stands the wheels turn by hand with brake off, and brakes apply as expected. Drove around town for 15-20 minutes, and coach is quieter, obviously stronger. Fan clutch not engaging because it is not dragging and causing extra work. Sigh.
The "L" bracket that supports MC from the top had worked loose, tightening that helped rigidity.
Progress!
Wow--that's 1/16". You must have been right at the hairy edge.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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