NEED Help! Front disc brakes won't release!

[1972RedNeck]

My 1972 GMC 3/4 ton 4X4 brakes won't release. The original brake booster went bad so I installed a NAPA brake booster. They worked fine before but now the brakes won't release all the way. They just drag and over heat the brakes (600 degrees F in 5 minutes on the rotors). The rod coming out of the booster is pressed hard against the fire wall and the pedal has about a 1/2 inch of free play. Is there any way to adjust it? Is it a faulty booster? This is a daily driver so I need help fast.


Any help is greatly appreciated.

[mdwilf]

Did they ever work correctly after the new booster?

If not, of course the problem is likely in the booster or the rods going to it - there are adjustments - look for a jamb nut on a threaded rod.

Next things to suspect are the rubber lines to the brakes - sometimes they can look fine, but collapse on the inside. If you replace one, always do both.

The proportioning valve - if the valve inside gets "slid" too far to one side, you can sometimes loosen the line to the opposite brakes & press the pedal & slide it back.

Hope this helps & post what you find out.

[cdowns]

doubt both rubber lines fail at exact same time

push rod adhustment should solve problem

[rsavage]

There is a small adjustable rod in the front of the booster that contacts the piston in the master cylinder. If it is too long it will preload the MC, and if it is too short it won't feel like the booster is working. You can adjust it by unbolting the MC from the booster and carefully moving the MC with lines attached forward. Don't let the MC stand on the brakelines alone for support - use a bungie to the hood hinges while you are adjusting it. Sometimes it takes a few tries.

[ubtripn]

Probably unrelated but don't foget the white lithium on the caliper bolts. Believe it or bot, this was why my disc brakes would not release. Your problem sounds differetnt but just wanted you to know.

[truckster]

Originally Posted by rsavage

There is a small adjustable rod in the front of the booster that contacts the piston in the master cylinder. If it is too long it will preload the MC, and if it is too short it won't feel like the booster is working. You can adjust it by unbolting the MC from the booster and carefully moving the MC with lines attached forward. Don't let the MC stand on the brakelines alone for support - use a bungie to the hood hinges while you are adjusting it. Sometimes it takes a few tries.

Your new booster should have come with instructions on how to adjust the rod. I can tell you from experience, it will definitely bind up the front brakes. What happens is that it doesn't let the piston move all the way back, and then pressure builds up in the calipers every time you use them. After a couple of applications, my Blazer wouldn't even move. Then I decided to read the instructions....

If you don't have the instructions, here's a link:

http://www.cardone.com/english/club/...s/93039354.asp

[1972RedNeck]

I just pulled the master cylinder off last night. It is a solid rod between the MC and booster. I put 3 flat washer on each stud, bolted the master cylinder on and it works fine. Is there anything wrong with leaving it this way? I saw no adjustment.


Thanks

[rsavage]

Here is a photo of the rod that comes out of the front of the booster and goes into the back of the MC. It takes a 5/16" wrench. I have never had a booster without one. You can see that the end is threaded out some on mine.

[1972RedNeck]

Mine is just a solid 3/8 rod.

[alsriv2]

Is the rod from your old setup still available? If so, try to swap the "new" rod with the old one. I am not a fan of adding shims (washers) to the setup but that is me.
Another possibility would be to shorten the new rod by the thickness of the washers that were installed.

Al
'69 GMC 2500 Custom Camper
'69 Chevy C10 396 (engine in machine shop)