| [GMCnet] Gmc brake problem [message #270775] |
Thu, 29 January 2015 18:30  |
Advanced Concept Ener
Messages: 112
Registered: December 2014
Karma: 0
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Senior Member |
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Hal could you give me a little more detail about the seal between the master cylinder and booster. Ken put a new booster ( second new one) and put one of my previously replaced standard master cylinder back in and got better pedal. Just wonder if it was just a better fit that I could improve more with your seal fix.
Sean when the weather clears we should get together. That machine clip was interesting and maybe I can find one around here.
Thanks again for everyone's input.
Sent from my iPad
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| Re: [GMCnet] Gmc brake problem [message #270778 is a reply to message #270775] |
Thu, 29 January 2015 18:52  |
Hal StClair
Messages: 971
Registered: March 2013
Location: Rio Rancho NM
Karma: -12
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I used a piece of 1/4" closed cell foam and just cut it to fit between the master and booster. I don't want to bring up a sore subject and infer there is a miss match between the two which causes the vacuum leak but it stopped the aux pump from cycling.
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] Gmc brake problem [message #270793 is a reply to message #270775] |
Thu, 29 January 2015 21:03 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Sir, there is a seal between the booster and the mc. It fits around the pushrod snugly but if a previous life the booster hole is pitted from rust the seal will leak. I believe there is also two diff seals available but my memory isn't working. Maybe Rob will chime in as he did a study on it and I was just a bystander. Also check the check valves and I have seen where a po tried to put the support bracket between the booster and mc. Maybe take the extra reserve tank out of the system temporaly to see if it makes any diff. If the emergency brake is adjusted before the brake shoes it could give you a false sense of shoe contact. When adjusting the rear shoes make sure the emergency cable and lever is seated relaxed then adjust the brake shoes till locked tight. This will center the shoes in the drum, them back them off till the drum will ring when tapped with the wrench and not drag. I have also found some coaches to get to bleed all the air out I have had to jack and block the rear and deflate the bags and jack the arms up high to get the bleeders and the line above the T in the flex line.
Advanced Concept Ener wrote on Thu, 29 January 2015 19:30Hal could you give me a little more detail about the seal between the master cylinder and booster. Ken put a new booster ( second new one) and put one of my previously replaced standard master cylinder back in and got better pedal. Just wonder if it was just a better fit that I could improve more with your seal fix.
Sean when the weather clears we should get together. That machine clip was interesting and maybe I can find one around here.
Thanks again for everyone's input.
Sent from my iPad
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C. Boyd
76 Crestmont
East Tennessee
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| Re: [GMCnet] Gmc brake problem [message #270801 is a reply to message #270796] |
Thu, 29 January 2015 22:08 |
GMC.LES
Messages: 505
Registered: April 2014
Karma: -2
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Senior Member |
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I'm very interested in seeing what info Rob is going to provide regarding the booster seal. But, I am having trouble seeing how this seal would cause the issues that Jon is experiencing. Someone steer me straight if I have missed something here.
Jon has stated that he has a high, firm pedal when the engine is not running and no vacuum. He has also stated he has a very low pedal with engine running and full vacuum applied. This tells me that the booster is functioning, maybe not perfectly, but it is working. He also states that he had very little braking effect at the rear wheels.
There are a few questions that have not been asked yet, but might have been addressed by Ken Frey. I'd like the hear what Jon has to report after picking up his coach.
A few questions I'd like to hear the answers to:
1) When Jon replaced the rear shoes for the second time, what was the wear pattern on the shoes he removed? Did they show contact the full length of the lining, or just around the center of the arc?
2) Prior to changing the rear shoes for the second time, did he attempt to properly adjust them to restore the pedal height and braking function?
3) During hard braking, was he at any time able to lock up the front wheels?
4) During hard braking, does the coach pull to the left or right?
I'm also having a hard time believing it is just rear shoe related. This sounds much like it is combination of small issues all adding together to create one big bad result.
Les Burt
> On Jan 29, 2015, at 10:10 PM, Robert Mueller wrote:
>
> Chuck,
>
> I called Ken Frey and had a chat with him about this problem and I'm working on a response that doesn't piss anyone off! ;-)
>
> Regards,
> Rob M.
> The Pedantic Mechanic
> Sydney, Australia
> AUS '75 Avion - The Blue Streak TZE365V100428
> USA '75 Avion - Double Trouble TZE365V100426
>
>
> -----Original Message-----
> From: Charles Boyd
>
> Sir, there is a seal between the booster and the mc. It fits around the pushrod snugly but if a previous life the booster hole is
> pitted from rust the seal will leak. I believe there is also two diff seals available but my memory isn't working. Maybe Rob will
> chime in as he did a study on it and I was just a bystander. Also check the check valves and I have seen where a po tried to put
> the support bracket between the booster and mc.
> Maybe take the extra reserve tank out of the system temporaly to see if it makes any diff. If the emergency brake is adjusted
> before the brake shoes it could give you a false sense of shoe contact. When adjusting the rear shoes make sure the emergency cable
> and lever is seated relaxed then adjust the brake shoes till locked tight. This will center the shoes in the drum, them back them
> off till the drum will ring when tapped with the wrench and not drag. I have also found some coaches to get to bleed all the air
> out I have had to jack and block the rear and deflate the bags and jack the arms up high to get the bleeders and the line above the
> T in the flex line.
>
> C. Boyd
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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