Rear brake problem - The 1947 - Present Chevrolet & GMC Truck Message Board Network

chevyboy55 · 08-03-2008, 10:41 PM

Ok here's the story from the beginning. My sons 72 was out of brake fluid in the rear chamber of the master cylinder,I found the left rear wheel cylinder was leaking.I replaced it with a brand new wheel cylinder,new shoes,bled brakes etc. Then we were servicing it later(don't remember how long due to it being off the road for 11/2 years for paint & rebuild) & it was dry again.Same routine as before,new wheel cylinder,shoes etc.This time I was being extra careful to make sure that I did not snag or some how tear the rubber on the wheel cylinder. Well as you are I'm sure guessing by now it's dry again! What in the heck can be the cause of this?

68gmsee · 08-03-2008, 10:56 PM

I'm assuming you have power brakes on this one. If you don't, is it possible that it's leaking into the carpet or somewhere inside the firewall?

If you don't see a leak then the only guess is that there's still some empty air space in the lines somewhere. Brake fluid can boil from brakes that get overheated due to some malfuntion, but as far as evaporating into thin air, I don't think that would be the case.

At this point, I would make absolutely sure that all of the air is out of the brake lines and monitor it carfully for leaks.

dwcsr · 08-03-2008, 11:04 PM

My bet is its leaking into the booster. It can't evaporate so it has to be a visable leak outside or into the booster.

chevyboy55 · 08-03-2008, 11:04 PM

Quote:

Originally Posted by 68gmsee

I'm assuming you have power brakes on this one. If you don't, is it possible that it's leaking into the carpet or somewhere inside the firewall?

If you don't see a leak then the only guess is that there's still some empty air space in the lines somewhere. Brake fluid can boil from brakes that get overheated due to some malfuntion, but as far as evaporating into thin air, I don't think that would be the case.

At this point, I would make absolutely sure that all of the air is out of the brake lines and monitor it carfully for leaks.

Yes it's got power brakes.I guess I forgot to add that yes I can see that it's leaking,I just can"t understand why the left rear only seems to be lasting about a couple months.

Longhorn Man · 08-03-2008, 11:16 PM

Are the shoes out of adjustment? If they are way out, then this can cause the pistons to basicly over extend.
Also if there is a lot of rust in the system it'll cause them to go bad, but not in that quick amount of time though.

08-03-2008, 10:41 PM	#1
chevyboy55 Senior Member Join Date: Aug 2004 Location: Kelso,Wa Posts: 3,637	Rear brake problem Ok here's the story from the beginning. My sons 72 was out of brake fluid in the rear chamber of the master cylinder,I found the left rear wheel cylinder was leaking.I replaced it with a brand new wheel cylinder,new shoes,bled brakes etc. Then we were servicing it later(don't remember how long due to it being off the road for 11/2 years for paint & rebuild) & it was dry again.Same routine as before,new wheel cylinder,shoes etc.This time I was being extra careful to make sure that I did not snag or some how tear the rubber on the wheel cylinder. Well as you are I'm sure guessing by now it's dry again! What in the heck can be the cause of this? __________________ Great minds think alike,So do ours

08-03-2008, 10:56 PM	#2
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Rear brake problem I'm assuming you have power brakes on this one. If you don't, is it possible that it's leaking into the carpet or somewhere inside the firewall? If you don't see a leak then the only guess is that there's still some empty air space in the lines somewhere. Brake fluid can boil from brakes that get overheated due to some malfuntion, but as far as evaporating into thin air, I don't think that would be the case. At this point, I would make absolutely sure that all of the air is out of the brake lines and monitor it carfully for leaks.

08-03-2008, 11:04 PM	#3
dwcsr Hollister Road Co. Join Date: Apr 2005 Location: Houston Posts: 6,134	Re: Rear brake problem My bet is its leaking into the booster. It can't evaporate so it has to be a visable leak outside or into the booster.

08-03-2008, 11:16 PM	#5
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Rear brake problem Are the shoes out of adjustment? If they are way out, then this can cause the pistons to basicly over extend. Also if there is a lot of rust in the system it'll cause them to go bad, but not in that quick amount of time though.



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