Interesting Master Cylinder Problem
Thread Starter
Racer
Joined: Dec 2000
Posts: 472
Likes: 0
From: Springfield GA
Interesting Master Cylinder Problem
I've bleed the brakes using a powerbleeder several times & they seem to be alright with the exception of that soft pedal (using silicon DOT 5 fluid). The problem is I keep getting brake fluid out from under the rubber MC lid seal. I've tried several different seals & 2 sets of tight fitting bails & I still have the same problem. It just pours out of the rear reservoir (after I use the brakes & put pressure on it) & I've checked & the fluid in both reservoirs is a good 1/2" down from the top, so it's not overfilled. What could be causing this problem? Good thing I'm using silicon fluid or my frame paint would be ruined! 
I must be missing something..............what's the problem? I've never had this happen before.
I must be missing something..............what's the problem? I've never had this happen before.
Thread Starter
Racer
Joined: Dec 2000
Posts: 472
Likes: 0
From: Springfield GA
One more question pertaining to this problem. Is it possible if the lid seal isn't tight, to suck air back into the MC and the system requiring a MC/line rebleed? My pedal after this happened is just way too soft.
Thread Starter
Racer
Joined: Dec 2000
Posts: 472
Likes: 0
From: Springfield GA
Race Director
Joined: Sep 2001
Posts: 10,560
Likes: 439
From: Wellington, FL
St. Jude Donor '11 thru '25
I've bleed the brakes using a powerbleeder several times & they seem to be alright with the exception of that soft pedal (using silicon DOT 5 fluid). The problem is I keep getting brake fluid out from under the rubber MC lid seal. I've tried several different seals & 2 sets of tight fitting bails & I still have the same problem. It just pours out of the rear reservoir (after I use the brakes & put pressure on it) & I've checked & the fluid in both reservoirs is a good 1/2" down from the top, so it's not overfilled. What could be causing this problem? Good thing I'm using silicon fluid or my frame paint would be ruined! I must be missing something..............what's the problem? I've never had this happen before.
I must be missing something..............what's the problem? I've never had this happen before.
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
I only use DOT5 in my vehicles and never a problem. I have read in here/heard that you should boil it and let it sit to get all the small air bubbles out that got there from agitation in shipping, but have never needed to do that myself. For the seal try a new lid, sounds like the edge of the seal is slipping from in between the MC and the lis on the inside. Have you checked your rotors for runout? This can cause the calipers to suck in air around the pistons but not necessari;y leak juice out on the floor. I would go thru that first and lastly suspect a brand new MC. You didn't say if you were getting bubbles when you bled the brakes, if so, did you get then right away or did it take a while?
Thread Starter
Racer
Joined: Dec 2000
Posts: 472
Likes: 0
From: Springfield GA
I only use DOT5 in my vehicles and never a problem. I have read in here/heard that you should boil it and let it sit to get all the small air bubbles out that got there from agitation in shipping, but have never needed to do that myself. For the seal try a new lid, sounds like the edge of the seal is slipping from in between the MC and the lis on the inside. Have you checked your rotors for runout? This can cause the calipers to suck in air around the pistons but not necessari;y leak juice out on the floor. I would go thru that first and lastly suspect a brand new MC. You didn't say if you were getting bubbles when you bled the brakes, if so, did you get then right away or did it take a while?
Racer
Joined: Mar 2006
Posts: 366
Likes: 1
From: Houston Texas
Check that the reservoir cap is not warped. I chased this one for several months and found my cap would rock slightly on a flat surface. A few hammer taps, the cap was flat again; completely fixed it.
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