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nicevilledave
Just visiting
Member # 64
Posts: 9
From: niceville florida
Registered: 2/14/04
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posted 2/14/04 5:09:21 PM
The pedal on my '71 T-top goes to the floor on the 1st push; with about 3 pumps the pedal pressure comes up, but is still not firm. Its a manual system. I've had the master cylinder replaced 3 times (1 original change and 2 warranty replacements). Each time after replacing the MC, I lost the pedal after almost exactly 3 driving miles and had to pump the pedal to stop. The garage that replaced the MCs, subsequently recommended replacing the proportional valve. Had that done, but the pedal still went to the floor after about 3 miles. The garage claims they don't know what else to do,i.e., there is nothing else they want to do. I can't claim to be much of a mechanic and am at a loss to troubleshoot it further. The car really isn't drivable now. Anyone have a recommendation?
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blasterfdc
Just visiting
Member # 63
Posts: 5
From: maryland
Registered: 2/14/04
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posted 2/14/04 5:15:57 PM
Sounds like air in the system. Are you loosing any fluid? possible leak but if not should be just air and in need of a good brake bleed.
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nicevilledave
Just visiting
Member # 64
Posts: 9
From: niceville florida
Registered: 2/14/04
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posted 2/15/04 10:19:15 AM
Thanks for the reply. But not losing fluid. The garage gravity bled the system each time they changed the MC and, thinking just as you, I bled the system myself when I got the car home. The pedal firmed up, but it didn't last more than about 3 driving miles. Also none of the calipers are hot so I don't think the fluid is breaking down.
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blasterfdc
Just visiting
Member # 63
Posts: 5
From: maryland
Registered: 2/14/04
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posted 2/15/04 10:22:46 AM
Did they bench bleed the master cylinder before they installed it? That is a quick way to destroy a master cylinder in a hurry.
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nicevilledave
Just visiting
Member # 64
Posts: 9
From: niceville florida
Registered: 2/14/04
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posted 2/15/04 5:28:30 PM
Don't know. Do you mean they should have or should not have?
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blasterfdc
Just visiting
Member # 63
Posts: 5
From: maryland
Registered: 2/14/04
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posted 2/15/04 6:28:03 PM
They have to. When installing a new master cylinder it is required that you bleed it on the bench before installing it into the car. If this is not done it can cause premature failure of the master cylinder. It isn't hard to do. All you have to do is hook up lines on the master cylinder and run them up into the bowl. Then push the plunger as if you were pumping the breakes until there are no air bubbles someing out. Then install in the car and bleed the entre brake system.
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nicevilledave
Just visiting
Member # 64
Posts: 9
From: niceville florida
Registered: 2/14/04
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posted 2/16/04 3:33:41 PM
The problem acts like a bad master cylinder. The manual brake system is pretty straight forward...pedal to MC to proportional valve to calipers. Its not leaking fluid. My troubleshooting leads me to start again with a new MC. But a question still lingers, is there anything else that could cause the "no pedal" after just a few miles of driving?
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JohnSeventyOne
Just visiting
Member # 68
Posts: 3
From: Greensboro, North Carolina
Registered: 2/19/04
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posted 2/19/04 5:11:52 PM
This may be one of those cases where your rotor may be pumping air into your brake system. As I have been told one or more of your rotors could be off by a few thousands (in and out) and when you drive it will wobble in and out causing the disk pads to pump in and out forcing air into the system past the O-Ring seals. When you think about it after 3 miles the rotor has turned 1-2 thousand times. Any offset by even 1 thousands of a inch will cause a considerable amount of pumping of air. Have your rotors checked for out of round. Start at the back first. Just my 2 cents worth.
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nicevilledave
Just visiting
Member # 64
Posts: 9
From: niceville florida
Registered: 2/14/04
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posted 2/21/04 10:56:45 AM
Thanks for the ideas/recommendations. I've had the car since I bought it off the Dorr Chevrolet (Milan, Ohio) showroom floor December 31, 1970. It's always been a "driver;" now has a little over 150K miles on it. I've taken it all across the continental US and to Hawaii and Germany and back. The rotors are original as are the wheel bearings. So I'll start by checking the rotor roundout and bearings. Will post what I find and how I fix the brakes. Unfortunately I see this as a couple month "project."
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nicevilledave
Just visiting
Member # 64
Posts: 9
From: niceville florida
Registered: 2/14/04
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posted 2/21/04 4:41:29 PM
...make that "check rotor runout".
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nicevilledave
Just visiting
Member # 64
Posts: 9
From: niceville florida
Registered: 2/14/04
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posted 4/27/04 6:30:51 PM
To close the loop on this thread:
Got rear rotors, front rotors and hubs from Muskegon Brake. Muskegon assembled and trued the front rotors and hubs, and checked the parallelism of the rear rotors before they sent them (a small additional charge). Also replaced the front wheel bearings and seals. Everything was "bolt off, bolt on." Discovered the left rear brake (the only one not recently replaced) was bad, so called Muskegon again and got a ss sleeved calipher from them.
While the car was still on blocks and the wheels off, I bled around the car, i.e., left rear, right rear, right front and left front, 4 times to ensure all the air was out of the system (My wife was in the cockpit working the pedal; once around would have been enough for her). Maybe overkill. But...
the pedal came up and stayed up..."no pedal" was my initial problem. See earler posts, the "professionals" had given up on the problem.
Only glich I encountered was that the new left rear calipher heated up when I test drove the car. Posted the problem around; replies focused on a bad rubber brake hose. Called Muskegon for a new rubber hose to the steel line (I was in no hurry). Got it, put it on and the calipher went "cool."
I'm not much of a shadetree mechanic, but got everything apart and back together (everything that came off was OEM...34 years old). A lot of grease, but no skinned knuckles. With e-posting help from this forum and C3VR, I was comfortable doing the job. I made Muskegon Brake my single parts source. They (I talked primarily to Justin) were easy to work with and I recommend them.
Total parts cost was about $590. My "unskilled labor" was about 6-7 hours, give or take, over 3 weeks or so.
Most importantly the car is drivable again.
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