| [GMCnet] brake pedal play amount erratic [message #143491] |
Thu, 15 September 2011 14:14  |
paul h cashman
Messages: 176
Registered: May 2005
Karma: 0
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Armand,
It sounds like, you are having , Residual Brake line Pressure .
That is exactly, what my brakes were doing, but got so hard ,you could not
push the Brake Pedal in, at all ,the Pedal got hard and applied the Brakes
and stopped me .
The residual pressure from the P-30 reservoir was causing my problem. I
reinstalled the old OEM Brake Reservoir.
That seemed to happen ,most often, after I released my line lock and the
inrush of Brake Fluid closed the Residual check Valves in the P-30
Reservoir.
Paul Cashman
Riverdale GA
78 Transmode
> I have about 3000 miles on a disc brake conversion that I did just before
I
> left on this trip. My brake pedal normally has what seems to be about an
> inch or inch and a half of pedal play when I step on it but occasionally
it
> has virtually no pedal play. When this happens the brakes still work fine
> with no other symptoms. I have been concerned but since they work fine
not
> overly concerned. Any ideas what is going on?
> --
> Armand Minnie
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Paul H Cashman
Riverdale Ga
1978 Transmode
1975 Corvette
1978 Beetle Convertible
1989 Harley Davidson Sportster
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| Re: [GMCnet] brake pedal play amount erratic [message #143526 is a reply to message #143525] |
Thu, 15 September 2011 21:21  |
armandminnie
Messages: 864
Registered: May 2009
Location: Marana, AZ
Karma: 2
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Rob, the hoses are all new braided SS hoses from Applied GMC - not that a new hose couldn't be bad but I am thinking that problem would be from old hoses.
Turns out that master cylinders can have residual pressure valves that are left over from drum brake uses. I would think that if there were a residual pressure valve in the MC then it would act the same all the time though.
Armand Minnie
Marana, AZ
'76 Eleganza II TZE166V103202
visit my gmc blog
click here to visit gmcws.org
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| Re: [GMCnet] brake pedal play amount erratic [message #143527 is a reply to message #143524] |
Thu, 15 September 2011 21:23 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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| armandminnie wrote on Thu, 15 September 2011 19:03 |
Paul, are you saying that the P-30 has a residual pressure valve or that it somehow causes it from some flaw? It does seem like there might be residual pressure in the lines but only one caliper seems to be affected if that is so.
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Armand,
I may be wrong, but I don't believe there would be any way for the MC to build up residual pressure unless it is defective, or it is not releasing all the way when you let off the brake pedal. The only way that would happen is if the push rod between the booster and the master cylinder were too long. That would have shown up right from the get go, when you were bleeding the brakes, not 3000 miles later, and it would not only affect one caliper. Is one wheel getting hotter than all the others?
Any other ideas out there?
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: [GMCnet] brake pedal play amount erratic [message #143528 is a reply to message #143527] |
Thu, 15 September 2011 21:28 |
armandminnie
Messages: 864
Registered: May 2009
Location: Marana, AZ
Karma: 2
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Senior Member |
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I did some research about residual pressure after Paul suggested that possibility and some MC's had check valves to hold pressure on drum brake shoes so the springs won't pull them back all the way. The check valve, according to what I read, is installed at the outlet for the rear brakes in a dual reservoir MC. Thing is it seems like it would be happening all the time and that if I pumped the brakes I could make it happen and neither of those is the case.
Armand Minnie
Marana, AZ
'76 Eleganza II TZE166V103202
visit my gmc blog
click here to visit gmcws.org
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| Re: [GMCnet] brake pedal play amount erratic [message #143531 is a reply to message #143526] |
Thu, 15 September 2011 21:43 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Armand,
Number 1: A) Agreed
B) Agreed
Number 2: Agreed, but why only one wheel?
Regards,
Rob M.
Number 1: -----Original Message-----
From: Armand Minnie
A) Rob, the hoses are all new braided SS hoses from Applied GMC - not that a new hose couldn't be bad but I am thinking that problem
would be from old hoses.
B) Turns out that master cylinders can have residual pressure valves that are left over from drum brake uses. I would think that if
there were a residual pressure valve in the MC then it would act the same all the time though.
--
Armand
Number 2: -----Original Message-----
From: Armand Minnie
I did some research about residual pressure after Paul suggested that possibility and some MC's had check valves to hold pressure on
drum brake shoes so the springs won't pull them back all the way. The check valve, according to what I read, is installed at the
outlet for the rear brakes in a dual reservoir MC. Thing is it seems like it would be happening all the time and that if I pumped
the brakes I could make it happen and neither of those is the case.
--
Armand
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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] brake pedal play amount erratic [message #143637 is a reply to message #143527] |
Sat, 17 September 2011 10:10 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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A sticking caliper will produce these symptoms.
--johnny
--- On Fri, 9/16/11, Carl Stouffer <carljr3b@yahoo.com> wrote:
From: Carl Stouffer <carljr3b@yahoo.com>
Subject: Re: [GMCnet] brake pedal play amount erratic
To: gmclist@temp.gmcnet.org
Date: Friday, September 16, 2011, 2:23 AM
armandminnie wrote on Thu, 15 September 2011 19:03
> Paul, are you saying that the P-30 has a residual pressure valve or that it somehow causes it from some flaw? It does seem like there might be residual pressure in the lines but only one caliper seems to be affected if that is so.
Armand,
I may be wrong, but I don't believe there would be any way for the MC to build up residual pressure unless it is defective, or it is not releasing all the way when you let off the brake pedal. The only way that would happen is if the push rod between the booster and the master cylinder were too long. That would have shown up right from the get go, when you were bleeding the brakes, not 3000 miles later, and it would not only affect one caliper. Is one wheel getting hotter than all the others?
Any other ideas out there?
--
Carl S.
'75 ex Palm Beach
Tucson, AZ.
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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] brake pedal play amount erratic [message #143682 is a reply to message #143670] |
Sat, 17 September 2011 21:00 |
hal kading
Messages: 642
Registered: February 2004
Location: Las Cruces NM
Karma: 4
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Senior Member |
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I'm betting there is a restriction in the new hose to the caliper. It is possible when the hose was manufactured that a flap was shaved off the inside of the hose and it is acting as a check valve. I have never seen it in a teflon hose - maybe a first time.
Hal Kading 78 Buskirk Las Cruces NM
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