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Old 10-29-2015, 07:49 AM   #1
65 Fastback
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Rear Drum Brakes Locked Up

Hi all, I have a problem I'm hoping someone can help me with.

My 72 C10 has always had a heavy Brake Pedal with little travel, i assumed it was normal not owning a truck before. Drums rear, Discs front.

Since i put in a rebuilt engine it has been even harder with less travel, i guessed the new motor was producing less vacuum.

Today i did an emergency stop and really put the boot into the pedal. The rear tyres didn't lock up, but when i went to move again it was obvious the brakes were not releasing. I was able to get it home and I jacked up the rear, put it in neutral and was unable to spin either wheel. I could however spin both front wheels easily. When i looked underneath the main hose to the T Block going to each rear drum was blown.

2 Hours later i could spin the rear wheels.

Im guessing the hose blew because of the pressure i put in the line when i stomped on it and it didn't bleed back to the master cylinder?

Is there an adjustment i need to make on the master cylinder/booster that would solve the issue of hard pedal and minimal travel?

Any insights appreciated. Pics below. Oh yeah and what the clamp on the rear brake line in the pic? is this some kind of budget proportioning valve?

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Old 10-29-2015, 01:55 PM   #2
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Re: Rear Drum Brakes Locked Up

First off, get rid of that clamp! I can't imagine what it is there for (line lock for transport?). Looks like it is restricting the flow. It has probably also damaged the hose. Secondly, replace the rubber hose incase there is any damage regardless of whether it looks OK or not. The inner lining of rubber hoses can delaminate and cause a blockage, and the hose can remain kinked even when the clampis removed.
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Old 10-29-2015, 04:04 PM   #3
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Re: Rear Drum Brakes Locked Up

sounds like the wheel cyl. shot
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Old 10-29-2015, 05:55 PM   #4
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Re: Rear Drum Brakes Locked Up

with the new master and booster did you set up the pushrods for proper clearance/ as listed in the factory service manual
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Old 10-29-2015, 06:29 PM   #5
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Re: Rear Drum Brakes Locked Up

You will probably have to reset plunger in the proportion valve
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Old 10-29-2015, 07:25 PM   #6
65 Fastback
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Quote:
Originally Posted by cdowns View Post
with the new master and booster did you set up the pushrods for proper clearance/ as listed in the factory service manual
It was in truck when I bought it. Does anyone know the procedure?
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Old 10-29-2015, 07:34 PM   #7
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Re: Rear Drum Brakes Locked Up

Holy crud! You were driving it like that? That clamp is a device used to close off the flow of fluid when doing repairs.
Prop valve as stated above has probably cut off flow to the rear as it is designed to do in the event of a failure.
I would inspect the entire system for anything out of the ordinary such as this clamp and replace that rubber hose also as stated above and get the proper stud for that tee as well. No zip ties on your brakes.
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Old 10-29-2015, 08:57 PM   #8
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Re: Rear Drum Brakes Locked Up

Quote:
Originally Posted by cdowns View Post
with the new master and booster did you set up the pushrods for proper clearance/ as listed in the factory service manual
Quote:
Originally Posted by 65 Fastback View Post
It was in truck when I bought it. Does anyone know the procedure?
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as Downs stated RTFSM, I'll send you mine if you don't have one
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Old 10-29-2015, 10:28 PM   #9
65 Fastback
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Thanks for the advice. I'll remove the clamp, change the hose and see if that sorts it out.
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Old 10-31-2015, 02:20 AM   #10
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Originally Posted by jaros44sr View Post
You will probably have to reset plunger in the proportion valve
Any idea how that's done? Couldn't find it in service manual. Cheers.
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Old 10-31-2015, 12:33 PM   #11
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Re: Rear Drum Brakes Locked Up

Section 5, BRAKES start at page 5-1 then go into special tools 5-32
index
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