Brake problems on my 78
Thread Starter
2nd Gear
Joined: Jul 2005
Posts: 2
Likes: 0
Brake problems on my 78
Just got a 78 L82 that was in storage for 12 years. Everything has been brought up to good order with the exception of the brakes, they are making me crazy. Brake reservoir rubber seal was gone, master cyl full of crud and calipers leaking. I replaced the master cyl, vaccume booster, brake proportion valve, and all callipers. Have bleed all calipers and master cyl with power bleeder. With out the engine running has good hard pedal. Start the engine and the pedal fades to the floor. Bleed some more and still same problem. Everything but the hard lines have been changed and there are no fluid leaks anywhere. Any ideas?
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
If the pedal goes to the floor, there is still air in the system somewhere. Did you bleed both halves of the rear calipers? Did fluid flow freely from all bleeders? Does the brake warning light come on when the pedal is depressed? The pedal travel should be about 21/2 inches with the engine running.
Thread Starter
2nd Gear
Joined: Jul 2005
Posts: 2
Likes: 0
I followed the procedure in the book where I bleed the right rear outside, rt rear inside, lf rear outside, lf rear inside, rt front and then the lf front. Same procedure each time. While bleeding each position I tapped on the calliper with a small hammer to dislodge any small air bubbles. On the final 3 or 4 rotations I had nothing but fluid. I used a transparrent line in a bottle of brake fluid just incase of air return. The brake pedal rod to the vaccume booster was the same length as the stock one removed and has no stop nut for pedal adjustment. When the engine is running and in gear I can initially stop the rotors (car is on blocks) but as the pedal fades the rotors start to slowly turn(loosing clamping pressure). So far I have run about 2 gallons of brake fluid thru the system. ????
Le Mans Master
Joined: Sep 2003
Posts: 8,812
Likes: 2,029
From: eastern NC
The only thing I see missing from your list of replaced parts (besides the hard lines) are the flexible hoses at each corner. Although I would not expect them to release pressure as you've indicated is happening. They can contribute to a spongy pedal or sticking caliper, but without leaking, will hardly release this much pressure.
By-the-way, because you replaced your master cylinder doesn't mean it isn't the problem, particularly if you replaced it with a rebuilt. Assuming there are no leaks, as you've indicated, it really sounds like the master cylinder is the culprit. The only time I've had a pedal go to the floor without losing fluid is when the master cylinder was leaking internally.
You might want to try a new one, or at least a known good one.
Good luck... GUSTO
By-the-way, because you replaced your master cylinder doesn't mean it isn't the problem, particularly if you replaced it with a rebuilt. Assuming there are no leaks, as you've indicated, it really sounds like the master cylinder is the culprit. The only time I've had a pedal go to the floor without losing fluid is when the master cylinder was leaking internally.
You might want to try a new one, or at least a known good one.
Good luck... GUSTO
Drifting
Joined: Oct 2004
Posts: 1,259
Likes: 7
From: Ontario
Originally Posted by GUSTO14
The only thing I see missing from your list of replaced parts (besides the hard lines) are the flexible hoses at each corner. Although I would not expect them to release pressure as you've indicated is happening. They can contribute to a spongy pedal or sticking caliper, but without leaking, will hardly release this much pressure.
By-the-way, because you replaced your master cylinder doesn't mean it isn't the problem, particularly if you replaced it with a rebuilt. Assuming there are no leaks, as you've indicated, it really sounds like the master cylinder is the culprit. The only time I've had a pedal go to the floor without losing fluid is when the master cylinder was leaking internally.
You might want to try a new one, or at least a known good one.
Good luck... GUSTO
By-the-way, because you replaced your master cylinder doesn't mean it isn't the problem, particularly if you replaced it with a rebuilt. Assuming there are no leaks, as you've indicated, it really sounds like the master cylinder is the culprit. The only time I've had a pedal go to the floor without losing fluid is when the master cylinder was leaking internally.
You might want to try a new one, or at least a known good one.
Good luck... GUSTO
Intermediate
Joined: Aug 2005
Posts: 33
Likes: 0
From: Olive Branch Ms
75 Brake problem
Originally Posted by Ken Barnes
Just got a 78 L82 that was in storage for 12 years. Everything has been brought up to good order with the exception of the brakes, they are making me crazy. Brake reservoir rubber seal was gone, master cyl full of crud and calipers leaking. I replaced the master cyl, vaccume booster, brake proportion valve, and all callipers. Have bleed all calipers and master cyl with power bleeder. With out the engine running has good hard pedal. Start the engine and the pedal fades to the floor. Bleed some more and still same problem. Everything but the hard lines have been changed and there are no fluid leaks anywhere. Any ideas?
Rob ***
Last edited by RAC396; Aug 15, 2005 at 08:31 AM.
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Instructor
Joined: Aug 2005
Posts: 104
Likes: 5
The system is designed to be relatively independant between front and rear. If you have no brakes at all then it has to be one of the common elements. 1. Master Cyl. 2. Booster (you will have brakes without the booster, just not power brakes) 3. Proportioning valve. Look at these items first!!
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
Originally Posted by 77 Vette Girl
The system is designed to be relatively independant between front and rear. If you have no brakes at all then it has to be one of the common elements. 1. Master Cyl. 2. Booster (you will have brakes without the booster, just not power brakes) 3. Proportioning valve. Look at these items first!!
The booster cannot affect the hydraulic brake system, only assist it. Without the engine running, the brake pedal should only move about 1/2 in., once the residual booster vacuum is bled off.
Intermediate
Joined: Aug 2005
Posts: 33
Likes: 0
From: Olive Branch Ms
Solved Brake problem
Originally Posted by Ken Barnes
Just got a 78 L82 that was in storage for 12 years. Everything has been brought up to good order with the exception of the brakes, they are making me crazy. Brake reservoir rubber seal was gone, master cyl full of crud and calipers leaking. I replaced the master cyl, vaccume booster, brake proportion valve, and all callipers. Have bleed all calipers and master cyl with power bleeder. With out the engine running has good hard pedal. Start the engine and the pedal fades to the floor. Bleed some more and still same problem. Everything but the hard lines have been changed and there are no fluid leaks anywhere. Any ideas?
Rob
