Brake question
Thread Starter
Racer
Joined: Jul 2004
Posts: 441
Likes: 1
From: Windsor Ontario
Brake question
I searched the past threads and read a lot of them, mostly they are about losing brake pedal, or slowly going to the floor.
My problem has been since I owned the car (5 years) the brakes work but the pedal is low to the floor, I rebuilt all 4 calipers, all new barke lines and hoses, no leaks any where, just put on a new master cylinder, I've bled them quite a few times, but still the same result. the pedal is close to the floor. any suggestions?
My problem has been since I owned the car (5 years) the brakes work but the pedal is low to the floor, I rebuilt all 4 calipers, all new barke lines and hoses, no leaks any where, just put on a new master cylinder, I've bled them quite a few times, but still the same result. the pedal is close to the floor. any suggestions?
Racer
Joined: Feb 2009
Posts: 343
Likes: 0
From: San Diego CA
I searched the past threads and read a lot of them, mostly they are about losing brake pedal, or slowly going to the floor.
My problem has been since I owned the car (5 years) the brakes work but the pedal is low to the floor, I rebuilt all 4 calipers, all new barke lines and hoses, no leaks any where, just put on a new master cylinder, I've bled them quite a few times, but still the same result. the pedal is close to the floor. any suggestions?
My problem has been since I owned the car (5 years) the brakes work but the pedal is low to the floor, I rebuilt all 4 calipers, all new barke lines and hoses, no leaks any where, just put on a new master cylinder, I've bled them quite a few times, but still the same result. the pedal is close to the floor. any suggestions?
Le Mans Master
Joined: Aug 2006
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Likes: 1,554
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Low brake pedal.
In the 1966-1982 Corvette Shop Manual, page 10-6 under dual master cylinders it says "Two sources for MC are Delco Moraine and Bendix." Two primary pistons were used one has a deep socket for the push rod the other is very shallow. Could this be the problem? Anyone else ever heard of this? PG.
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
I searched the past threads and read a lot of them, mostly they are about losing brake pedal, or slowly going to the floor.
My problem has been since I owned the car (5 years) the brakes work but the pedal is low to the floor, I rebuilt all 4 calipers, all new barke lines and hoses, no leaks any where, just put on a new master cylinder, I've bled them quite a few times, but still the same result. the pedal is close to the floor. any suggestions?
My problem has been since I owned the car (5 years) the brakes work but the pedal is low to the floor, I rebuilt all 4 calipers, all new barke lines and hoses, no leaks any where, just put on a new master cylinder, I've bled them quite a few times, but still the same result. the pedal is close to the floor. any suggestions?
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Burning Brakes
Joined: Jan 2009
Posts: 1,224
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From: Clarksville Indiana
Theres a long post on here that explains why it makes no difference if you start at one caliper or another, it made sence the way it was explained, and it also referenced two different manuals that say the exact opposite of each other. The important thing I got was that you want to bleed the inboard bleeder on the rear and then the outboard one. Can you pump it 2-3 times as your stopping and get a good pedal? If you can or cant, means/indicates something I think, little foggy on what though..lol If your brake work and parts are all good, I would think maybe something in the pedal to booster or booster to m/c may be out of ajustment or incorrect?
Last edited by 71coupe454; Mar 23, 2009 at 09:09 AM.
Le Mans Master
Joined: Aug 2006
Posts: 7,417
Likes: 1,554
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Low Pedal
Power booster: Step on and release the brake pedal several times to bleed off any vacuum, apply light pressure on the brake pedal and start the motor, pedal should move to floor.
If a booster is bad it will take very hard pedal pressure to stop the car. PG.
Team Owner
Joined: Mar 2002
Posts: 24,160
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In the 1966-1982 Corvette Shop Manual, page 10-6 under dual master cylinders it says "Two sources for MC are Delco Moraine and Bendix." Two primary pistons were used one has a deep socket for the push rod the other is very shallow. Could this be the problem? Anyone else ever heard of this? PG.
Mismatching a deep well piston with a shallow booster rod will cause what's happening to you. Pop off the MC and make sure that isn't the case.
Also there are 2 different pedal rod lengths for the booster. C3s need the longer one. Some guys have mistakenly swapped in the booster with the shorter rod. In this case, your pedal will often not return to its correct height leaving the brake light on. The previous owner of my car made this mistake, and drove around for years like that.
I ended up building an extension for the pushrod with a length of threaded rod and a coupling nut.
Thread Starter
Racer
Joined: Jul 2004
Posts: 441
Likes: 1
From: Windsor Ontario
I did bench bleed the M/C before i started, I bled the rear brakes with the wheels off and bled both bleeders. When I pump the pedal there is no change in the height, I'll check the push rod length going into the M/C and see if that's the issue.
Team Owner
Joined: Mar 2002
Posts: 24,160
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Is the pedal resting/returning to the proper height and turning off your brake lights?
Thread Starter
Racer
Joined: Jul 2004
Posts: 441
Likes: 1
From: Windsor Ontario
The pedal returns all the way to the top, everytime. You can feel resistence on the pedal all the way down, so it's not free play, but it doesn't feel like it engages the brakes until almost to the floor.
When stopped, I can push harder on the pedal and actually feel the hard stop for the pedal. They work, very well, but I feel that the pedal hieght should be higher when the brakes engage, maybe it's fine and it's just my thinking of newer brake systems, as opposed to 35 year old systems.
When stopped, I can push harder on the pedal and actually feel the hard stop for the pedal. They work, very well, but I feel that the pedal hieght should be higher when the brakes engage, maybe it's fine and it's just my thinking of newer brake systems, as opposed to 35 year old systems.
Team Owner
Joined: Mar 2002
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The pedal returns all the way to the top, everytime. You can feel resistence on the pedal all the way down, so it's not free play, but it doesn't feel like it engages the brakes until almost to the floor.
When stopped, I can push harder on the pedal and actually feel the hard stop for the pedal. They work, very well, but I feel that the pedal hieght should be higher when the brakes engage, maybe it's fine and it's just my thinking of newer brake systems, as opposed to 35 year old systems.
When stopped, I can push harder on the pedal and actually feel the hard stop for the pedal. They work, very well, but I feel that the pedal hieght should be higher when the brakes engage, maybe it's fine and it's just my thinking of newer brake systems, as opposed to 35 year old systems.
Hmm ... I just reread your first post.
"slowly going to the floor"
Ok, normally that means the piston seal(s) have gone out in your MC and the fluid is bypassing internally. I know you said you just replaced it, but maybe you got a lemon. The easiest way to test this theory is to pull both hardlines out and plug the holes. Then start up the car and put slow and steady pressure on the pedal. If if gradually sinks to the floor, then you've lost the MC pistons seal(s).
Last edited by wcsinx; Mar 23, 2009 at 04:48 PM.
Team Owner
Joined: Mar 2002
Posts: 24,160
Likes: 78
I think maybe you're just feeling the friction in the pedal works itself on the way down. Hopefully you just have mismatched MC because that's about the simplest thing to fix possible.
Is there a *pop* or a catch that the pedal seems to stick on as it's coming back up, or is it smooth all the way up and down?
Thread Starter
Racer
Joined: Jul 2004
Posts: 441
Likes: 1
From: Windsor Ontario
I didn't have time to check the newly installed M/C, but put my old one on the bench to see how it works, as there was no change after the swap, what I did notice, when I pushed the piston in the first half nothing happened.
I know there are two piston inside these, so was I pushing the first piston with nothing happening? and everything happening with the second piston?
Maybe I do have a bad one?
Can some one explain how these dual piston master cylinders work, thanx.
I know there are two piston inside these, so was I pushing the first piston with nothing happening? and everything happening with the second piston?
Maybe I do have a bad one?
Can some one explain how these dual piston master cylinders work, thanx.
Team Owner
Joined: Mar 2002
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That's actually what I thought might be happening to you 2 posts back. This is what the piston looks like...
There are 2 seals ... 1 for each reservoir/brake circuit. The forward seals seems to wear a bit faster than the rear, and when it gives out essentially you end up pressurizing both circuits with the rear seal. (And btw, don't listen to the guy who was linking design documents from Lexus to claim I was wrong about this.
) This condition will also give you excessive pedal travel. Now with that being said, I have never seen that happen with a new MC, but I suppose anything is possible.
There are 2 seals ... 1 for each reservoir/brake circuit. The forward seals seems to wear a bit faster than the rear, and when it gives out essentially you end up pressurizing both circuits with the rear seal. (And btw, don't listen to the guy who was linking design documents from Lexus to claim I was wrong about this.
) This condition will also give you excessive pedal travel. Now with that being said, I have never seen that happen with a new MC, but I suppose anything is possible.