Do I need need a new Master Cyclinder ?
Thread Starter
Pro
Joined: Feb 2005
Posts: 662
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From: Cedar Falls IA
Do I need need a new Master Cyclinder ?
Okay my "brake" light came on going to a show. Pulled the top off the Master Cylinder thinking it was low. Looked like water was in it. Drained the old fluid, lots of gunk in the Master Cylinder. Cleaned out everything replaced the fluid and bled the brakes. Now a month later the brake petal goes to the floor and the "brake" light is on again. I have checked for leaks and have not found any. No wet spots on the wheels or anything like that.
I thinking the Master Cylinder must be bad. Should I replace both the Master Cylinder and brake booster or ?? The Vette is a 1975. thanks for the help.+
I thinking the Master Cylinder must be bad. Should I replace both the Master Cylinder and brake booster or ?? The Vette is a 1975. thanks for the help.+
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
Your fluid is contaminated all the way to the calipers if you did not flush it. That is a problem with DOT3 and 4 fluid, it absorbs moisture which boils in the calipers and turns into steam which is bubbles which is a spring in a brake line. At this point I would completely drain, flush, refill and bleed the brakes and see where that gets you. May as well verify the rotor runout while your at it, that makes the calipers suck in air but not necessarily leak.
Thread Starter
Pro
Joined: Feb 2005
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From: Cedar Falls IA
Do I need a new Master Cyclinder ?
Okay everything has been flushed, cleaned and replaced. Still have no brake petal and "brake" light is still on. Master Cylinder ? Brake booster or both ? Vette is a 1975, thanks.
Race Director
Joined: Sep 2001
Posts: 10,560
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From: Wellington, FL
St. Jude Donor '11 thru '25
Originally Posted by Timbrr
Okay everything has been flushed, cleaned and replaced. Still have no brake petal and "brake" light is still on. Master Cylinder ? Brake booster or both ? Vette is a 1975, thanks.
Last edited by Jud Chapin; Nov 19, 2006 at 04:16 PM.
Thread Starter
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Joined: Feb 2005
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From: Cedar Falls IA
Do I need a new Master Cyclinder ?
After everything was flushed and cleaned the brakes were bled. The brakes can be pumped up a little but any pressure on the petal after that and it will go to the floor.
C6 the C5 of tomorrow
Joined: Nov 2000
Posts: 6,665
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From: Twin Cities Minnesota
Originally Posted by Jud Chapin
If the brake pedal will "pump up" after several pumps, that's a sign the mc is shot. The booster has nothing to do with the pedal going to the floor. While you did not mention that you bled the system, I assume you've done so as a small amount of air in the system will negatively affect the brake pedal, including having it go to the floor.
I disagree, if you pump the pedal and it comes up and stays up the the MC is OK.
If it doesn't come up the MC MAY be bad
If it comes up and drops when you put your foot on the brake the MC is definitly bad ( assuming no leaks )
Timbrr, I think your MC is shot!
Keith
Race Director
Joined: Sep 2001
Posts: 10,560
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From: Wellington, FL
St. Jude Donor '11 thru '25
It is really hard to say without being there with you. If you have successfully bled brakes before and are sure all air has been removed from the system, I would suspect the mc since you say you can pump up the pedal. One thing that I noticed is that you say you "drained the old fluid". If you allowed air to enter the mc by draining or sucking the fluid out of the mc, this can be difficult to remove. Anyway, perhaps others will have some ideas. I hate to tell you to replace the mc when it is not bad. Again, it's difficult to troubleshoot a brake system without being there.
Last edited by Jud Chapin; Nov 19, 2006 at 04:58 PM.
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