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Master Cylinder Failed?

choppedtop

Well-Known Member
Went to get fuel today before attending a car show some miles away. Everything was fine for around 10 stops. Got fueled up, pulled out of station, was pulling up behind the car at the stop sign, and no brakes.
Pedal to the floor. Lucky nobody was at the right of me or going either way on the main street, so I avoided hitting the car, ran the stop sign, made a quick right turn to make it into a parking lot. Limped back home with no problems or brakes.
Bottom line is I have no idea what happened. It is like the brake rod shortened its self by about 1 1/4 inches. That cannot happen. Took the cylinder apart ad could find nothing wrong. Put it back on, bled brakes and lengthened the push rod and have good brakes again. Ordered new cylinder, only because I could find nothing wrong with the old one, but have no trust in it now. The push rod is a mystery to me. It did not shorten its self. It was set up with 1/8 free travel and went to 1 1/4 free travel, with no adjustments coming loose. 10k trouble free miles, so I can't complain.
 
You say you had to lengthen the pushrod, then something must have happened to it ...... right?

Could the threads have stripped causing it to collapse? But with enough threads so that you could screw it out.
 
Check valve on the end of the master cylinder piston, did not seal. These are usually reed valves. Trash under then makes them total inoperable. Sometimes stabbing the pedal will dislodge the trash and restore function. You did right it, changing it out.
I would get a new push rod or locktite it after adjusting.
 
I figured out what happened on my brake issue. There is/was/should be, a little clip just behind the ball part of the push rod that goes into the front of the piston in master cylinder. For 10k miles this had never fully seated. When it did, the rod didn't have enough travel to push the piston at all. When I installed the new m/c with a new push rod, the same thing happened, but only after about 4 pushes on the brake while bleeding. SO!, make sure the pushd rod is fully seated in the piston receiver before calling it good. I think I am pretty fortunate that something bad didn't happen.
Just thought I would pass this along. Oh ya, I put in a 15/16 master cylinder instead of the 1 inch that I replaced. My brake pedal travels maybe 3/4" more, but it requires noticeable less foot pressure than before to make a quick stop.
 
Nice to see you got it sorted, the extra travel won't hurt it will give some extra feel (modulation) to the brakes.
 
Cool ..... Oklahoman's are so smart, even if some are from the wrong part of the state !!! :rolleyes:
 

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