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Old 08-23-2005, 01:22 AM
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Brakes locking up in non ABS system

I just purchased a Model T with stock Mustang V8, tranny, Corvette rear end and Corvette 4 wheel disk brakes. The car sat for 5 years in a garage. I started replacing old, tired parts. The problem: brake pedal was very hard. After new vacuum line was installed, stopping improved slightly but I felt a 2 stage stopping pattern. After slowing to stop, I would letting up & applying brakes again, brakes become hard again. Mechanic removed booster and said there was a hole in the diaphragm. Mechanic sent booster to be rebuilt. $386. Now all 4 brakes lockup frequently. Mechanic said change out flex brake lines to wheel. I did rears...no change. I noticed brake fluid was very, very dirty.
I changed brake fluid and master cylinder. No change. I took car back to mechanic, he sent booster back to the re-builder, a test was done and they said booster was working correctly. I got the car back, brakes still locking up. I jacked up car, pushed hard on the brake pedal and locked up the brakes, I released the fluid line after the master cylinder, front brakes still locked, I released out line from booster, front brakes freed. I repeated the test by locked the brakes up again, released pressure after booster, brakes freed again. Conclusion: rebuilt booster is bad? Is that the correct test and result?
This is not an ABS system. Using 4 Corvette disk brakes. Problem did not occur prior to rebuilding booster. Please note the unusual setup: brake pedal rod to master cylinder, 1 fluid line out to booster, booster has 1 fluid line out to a T connector, T has 2 fluid lines out to proportioning valve (1 front, 1 back), p valve has 3 lines out (2 to front brakes, 1 to rear brakes). While this set up appears to be very unusual it did work for more than 10 years prior to my buying the car and I did drive it home more than 50 miles with frequent hard stops. Bleeding brakes results in clear fluid. The rod from pedal into master cylinder is loose and floppy thus allowing plenty of room for the master cylinder to return to normal.
Any suggestions as to how to properly test the system and isolate the bad part, dirty parts or how to correct the situation, would be be greatly appreciated. The booster has been sent to a 2nd re-builder for a 2nd opinion as to its condition and functioning.
If I get the booster back and the system still locks up, I will try to extend the pedal rod 10 inches to a position where I have more room to install a new booster-2 chamber master cylinder unit (current master cylinder has only 1 chamber).
I have included 3 photos.
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Last edited by nprfan; 08-23-2005 at 01:27 AM. Reason: to make the story easier to read
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Old 08-23-2005, 04:45 AM
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lock up

Sorry didnt get time to read all that right now but I had lock up on my car
front one side

I took the brake caliper off and one of the pistons wouldnt come out a small and i mean small amount of compressed air got it out.

I replaced the seals on the piston and cleaned out the gunge that has acculimated and now its as good as gold
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Old 08-23-2005, 05:29 AM
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anti abs

A friend had a 55 Holden converted to power discs. It came off the road for a ground up and he had the booster chromed. Afterwards it would lock up and by chance (after everything else failed) we pulled out the vacuum hose and the wheels spun. Are the vent holes clear? is the diaphragm the right one etc. Borrow a known good booster and go from there.
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Old 08-23-2005, 07:38 AM
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Thanks to Ian and Keith for their replies

Thank you both for your quick replies. If I have time today I'll start cleaning the individual caliber pistons. I hope I get the booster back today. 2nd rebuilder has had it for more than a week.
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Old 08-23-2005, 07:39 AM
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Brake lock up

If the brake pedal rod is to long it will keep the brakes from releasing. The piston in the master needs to come back far enough to let the fluid bleed back into the master.
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Old 08-23-2005, 08:20 AM
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Quote:
Originally Posted by T-bucket23
If the brake pedal rod is to long it will keep the brakes from releasing. The piston in the master needs to come back far enough to let the fluid bleed back into the master.
The brake pedal rod is floppy loose and was checked by at least 2 mechanics.
Thanks for checking up on me.
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Old 08-23-2005, 07:59 PM
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bRAKES STUCK

My misses car had seased brake on one side.
When I took the caliper off it had 2 pistons one on each side of the disc
on the side that was stuck the brake pad was worn more than the the other .

Im talking about one pad on one side not the other side of the cars
just thought id clear that up.

Last edited by keithholden; 08-23-2005 at 08:08 PM.
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Old 08-24-2005, 12:07 PM
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Quote:
Is that the correct test and result?
That's pretty much textbook for that type of system.
http://imperialclub.com/Repair/Lit/M.../Page20-21.jpg
You might modify the test to loosen the line entering the booster, rather than exiting the master, to eliminate the possibility of the line itself being restricted.

Here's a link to the rest of that pamphlet, though hopefully it will just work right when you get the booster back.
http://imperialclub.com/Repair/Lit/Master/080/cover.htm

It's obviously a Chrysler pamphlet, but the booster-following-master setup is the same type.
From what I got out of it, it sounds like, for whatever reason, one side of your booster is open to atmospheric pressure even with no input from the master.
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Old 08-24-2005, 12:36 PM
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Quote:
If the brake pedal rod is to long it will keep the brakes from releasing.
Also, check to see that the actuator rod coming out of the booster isn't too long. This will cause locking as well,
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Old 08-24-2005, 12:37 PM
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Brakes locking up in non ABS system

Thanks to all who responded. I spoke with my neighbor last night and he suggested that I go directly into the proportional valve from the master cylinder. I did that this morning and WOW, WOW, WOW!!! No more locking up. I've only driven about 10 miles but I'm sure that it was the booster that was not rebuilt properly or put back together properly. Again, thank you to all. Frank
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