Brakes locking up

[gavin.biegler]

recently replaced my brake master cylinder (bench bled and bled brakes), and now the brakes are locking up after a short drive. if i unbolt the brake master cylinder the brakes immediately release so it seems the rod in the booster is too long. is it adjustable? i tried turning the rod clockwise some and measuring but it was hard to tell if it actually moved any.

 

[freeloader1969]

Is your new master cylinder a factory or aftermarket unit? Two things come to my mind, the piston in the bore (master) is sticking or the booster rod needs adjustment.

 

[gavin.biegler]

It is a brake best unit from oreillys. Yes bled calipers didn't measure how much fluid came out for bleeding but guessing 8+ oz

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[freeloader1969]

It is a brake best unit from oreillys. Yes bled calipers didn't measure how much fluid came out for bleeding but guessing 8+ oz

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I'm guessing you may need to get another master cylinder. It's possible that the one you put on, even though new, is defective. It certainly sounds like a sticking piston in the master cylinder bore.

 

[gavin.biegler]

I do have a motorcraft BMC on its way. I reinstalled the brakebest BMC yesterday doing my best to make sure the booster rod lined up correctly. Will rebleed tonight and see if it's better.
Do you know if the booster rod is adjustable? And how do you adjust it if it is.

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[gavin.biegler]

Update: took off the BMC and reinstalled I guess 3rd times the charm. Didn't really do anything different other than pay close attention to make sure the booster rod stayed lined up correctly.
Went for a 45 minute drive with some hard braking to get them heated up and everything went smoothly. Seems to be great!

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