67 brake problem
Thread Starter
Racer
Joined: Aug 2011
Posts: 291
Likes: 41
From: Springboro OH
67 brake problem
Installed all new correct rebuilt O ring calipers, discs, pads, and master cylinder in my 67. All from nationally recognized firms. Has a generic power booster and had a generic MC. Top bolts in booster were never installed, so installed nut plate and tightened bolts, but this moved booster very little.
Bore depth in both MCs is the same. Dot 4 fluid. Bled brakes and got a very high petal. Previously pedal would travel about half way.
Driving the vehicle and after a few brake applications the pads are locked up and do not retract.
Turned the clevis rod in 16 revolutions and petal is a little lower, but pads still lock up and will not retract.
What am I missing or is the new MC defective?
Thanks,
Tim
Bore depth in both MCs is the same. Dot 4 fluid. Bled brakes and got a very high petal. Previously pedal would travel about half way.
Driving the vehicle and after a few brake applications the pads are locked up and do not retract.
Turned the clevis rod in 16 revolutions and petal is a little lower, but pads still lock up and will not retract.
What am I missing or is the new MC defective?
Thanks,
Tim
Thread Starter
Racer
Joined: Aug 2011
Posts: 291
Likes: 41
From: Springboro OH
Burning Brakes
Joined: Mar 2005
Posts: 1,231
Likes: 34
From: Ontario
Check the M/C actuator rod
Check to see if the rod that actuates the master cyl ( sticking out of the booster ) is a little too long . If it is , the piston in the master will be actuated a little and the fluid will not return to the resovor . Which will hold pressure on the brakes .
Thread Starter
Racer
Joined: Aug 2011
Posts: 291
Likes: 41
From: Springboro OH
May put a couple of washers as spacers between the booster and the MC tomorrow to simulate a shorter rod and see if that solves the problem
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
If they sold you a drum-brake master cylinder (instead of a disc-brake cylinder), it has residual pressure valves inside the outlets (rubber item #2 in the illustration below), which will lock up the disc brakes. 
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Thread Starter
Racer
Joined: Aug 2011
Posts: 291
Likes: 41
From: Springboro OH
Yesterday I placed 2 washers on the studs between the booster and MC.
This seems to have solved the problem.
Will run this configuration for a while and if all continues fine I will shorten the rod 0.13 inches (the thickness of the 2 washers).
Still do not really understand why this was necessitated unless there is some difference in the internal configuration of the Master Cylinders.
Thanks to all that replied
Tim
This seems to have solved the problem.
Will run this configuration for a while and if all continues fine I will shorten the rod 0.13 inches (the thickness of the 2 washers).
Still do not really understand why this was necessitated unless there is some difference in the internal configuration of the Master Cylinders.
Thanks to all that replied
Tim
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
That could be part of the problem - in production, the pedal pushrod was length-preset, installed by Delco, and came to the plant as part of the booster assembly. The pushrod on the generic booster may not have been preset to the correct length by whoever made it.