I have a 1981 vette and having pedal fading after about 60 miles. I seem to lose about 1/4 in of fluid from the rear of the master cylinder.there is no sign of a leak at all of the lines and hoses.i have replaced everything from the master cylinder back.all new preformed lines, hoses,proportional valve.all new calipers,pads,and hand brake cables.the only thing I didn't replace were the rotors. it is an ongoing problem.when the pedal fades,i look at the master cylinder and it is low,with no sign of fluid again. when I bleed the line I get air at the left rear inner bleeder and a little air at the left inner bleeder. the rest of the bleeder it is all fluid,no air. I don't know where to look.i am totally frustrated.  HELP PLEASE!!!!!!!!!!!!

BILL

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did you replace the master cylinder? I believe it could be leaking where it meets the brake booster and possibly into the booster.

Its going somewhere that's for sure....you could loosen the MC without cracking the fluid lines and budge a bit and you will quickly fined the fluid if its leaking out the rear of the MC.These new iron MC's are prone to leaking. Chinese crap they are. The one on my car is new and leaking. The PO put it on about a year ago. I've got a Wilwood going on this weekend.

|UPDATED|3/27/2014 6:06:35 PM (AZT)|/UPDATED|


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My Christmas present to ME! Bought Sat 11-30-2013. 72, 350 4 spd, Silver with blue interior...Can't you just hear Pablo Cruz playing in the background?

If you are absolutely certain there is no fluid leaks from the rear calipers, then your master cylinder is most likely leaking into the booster. You can remove the two nuts holding the master to the booster and pull it forward easily, to look and see if it is wet back there. If it is, the master will need to be replaced again, or rebuilt.
Warped rotors can cause air in the system, no matter how many times you bleed it. With the springs behind the pistons of the calipers, the brake pads run against the rotors all the time. If a rotor is warped, the piston(s) will move in-out in their bores while driving, creating what is basically an air pump.....it will suck air into the brake system.
I think you prolly have 2 separate issues, and not just one causing your problems.

|UPDATED|3/28/2014 9:42:56 AM (AZT)|/UPDATED|


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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

i will check the master cylinder again. i check it about 3 mo ago and found nothing.maybe that is the problem. i"ll let you know. i did not turn the rotors,and i do feel a little pulsing when i brake.

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