70 Manual Brakes
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Joined: Mar 2003
Posts: 98
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From: Oglesby Illinois
70 Manual Brakes
I have a 70 Vette with manual brakes. When I step on the pedal it goes to the floor. If I pump it fast a few times it is firm and brakes well. Doesn't seem to loose pressure as long as my foot is firm on the pedal(10-20 seconds anyway). Once I let up on the pedal for a few seconds, the next time I press the pedal it goes to the floor again. I assume this is a master cylinder problem but not for sure. I don't feel the car pull one way or another during braking so I assume a caliper isn't leaking or doesn't have a lot of air in it. Just want some re-assurance before I change it out.
Former Vendor
Joined: Nov 2006
Posts: 2,482
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From: Carmichael ca
Does the pedal go to the floor if you push hard, easy or both? Have you tried bleeding the brakes? Finally, how are your rear wheel bearings? Excessive play in the bearings can push the rear pads out requiring a pump or two to get them back in.
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Joined: Mar 2003
Posts: 98
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From: Oglesby Illinois
hmm....I have not checked the fluid as I never saw any fluid of any type on the floor nor on the wheels, however I will check that to make 100% sure. That would be embarrasing!
So the test I did last night was sitting in the garage not moving. First press went all the way to the floor, pumped it a few times then very firm. Release pedal waited a few seconds, same thing. Pedal goes all the way to the floor, pump it a few times then solid. So I would assume if the rear bearings were bad that would only have an affect(or that dramatic of an affect) if the car was moving not sitting still. Does that make sense?
So the test I did last night was sitting in the garage not moving. First press went all the way to the floor, pumped it a few times then very firm. Release pedal waited a few seconds, same thing. Pedal goes all the way to the floor, pump it a few times then solid. So I would assume if the rear bearings were bad that would only have an affect(or that dramatic of an affect) if the car was moving not sitting still. Does that make sense?
Race Director
Joined: May 2006
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check the fluid level, if low you have a leak. the bearings being bad cause the pistons to not sit squarely resulting in air being sucked in while the car is rolling. Once the air is in the lines, sitting or moving make no difference.
Racer
Joined: Jan 2010
Posts: 367
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From: Christchurch Canterbury
Hi, I would start at the master cyl, check fluid levels, then check all the calipers for any leaks. Somethimes old brake flexi hoses will expand with pressure and "balloon" under pressure. If the fluid is topped off correctly and there is air in the system you have a leak somewhere, probably one of the calipers. Also pay to check there is no fluid on your floor mats as it maybe leaking from the rear of the master cylinder
Last edited by richiev88; Mar 15, 2010 at 06:11 PM. Reason: addition
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Joined: Nov 2000
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From: Twin Cities Minnesota
Be careful....This is how a few frame offs have started!
Good advice here, you have air somewhere, now you just have to find it.
One trick is to clamp off the 4 flex hoses (IF you have rubber hoses, clamping will destroy braided lines) If the pedal still drops you have a bad MC. If not undo one wheel at a time untill you find the culprit(s)
Good advice here, you have air somewhere, now you just have to find it.
One trick is to clamp off the 4 flex hoses (IF you have rubber hoses, clamping will destroy braided lines) If the pedal still drops you have a bad MC. If not undo one wheel at a time untill you find the culprit(s)
Safety Car
Joined: Sep 2007
Posts: 4,458
Likes: 331
From: Indy Indiana
theres lots of info on brakes on this forum,
do the simple thing first, bleed the brakes, use the gravity method, if you find air then that is your problem.
now what is the root cause of the air.. it is either out of fluid and the master cylinder reservior pumped air into the lines, so check the fluid level. if fluid level is ok then the calipers are letting air in. my car had one caliper last spring that had this problem.. I bled the caliper and drive it for 10 miles.. all was well, then 1 day later it had air in it again. I replaced it and all is well now. the one that shows air when you bleed is the bad one. cars that sit over the winter will have dried up seals and will let air in. if you have not driven the car alot then this may be the problem and it may not readilly show a leak. it may be letting air in but has not leaked enough fluid out to show.. the more you drive the car the more exercise the seals get and they won't dry up. this is a common problem with cars that sit alot. some here will tell you to get the expensive O-Ring sealed calipers to solve this problem.. but a 60$ autozone caliper and regular exercise solves the problem too.
do the simple thing first, bleed the brakes, use the gravity method, if you find air then that is your problem.
now what is the root cause of the air.. it is either out of fluid and the master cylinder reservior pumped air into the lines, so check the fluid level. if fluid level is ok then the calipers are letting air in. my car had one caliper last spring that had this problem.. I bled the caliper and drive it for 10 miles.. all was well, then 1 day later it had air in it again. I replaced it and all is well now. the one that shows air when you bleed is the bad one. cars that sit over the winter will have dried up seals and will let air in. if you have not driven the car alot then this may be the problem and it may not readilly show a leak. it may be letting air in but has not leaked enough fluid out to show.. the more you drive the car the more exercise the seals get and they won't dry up. this is a common problem with cars that sit alot. some here will tell you to get the expensive O-Ring sealed calipers to solve this problem.. but a 60$ autozone caliper and regular exercise solves the problem too.
