MGB Weird Brake issue finally solved.

[EricJNewman]

I've had this 79 MGB for a couple of years now. Previous Owner had replaced almost all the brake components, and the brakes were still terrible. Good hard pedal, but poor stopping power. Unable to lock brakes at any speed. Dangerous to drive, so they sold it. I checked everything, and it all seemed to be good components, bled properly, but no stopping power. Over several months, I slowly replaced everything even remotely suspect. New booster, Master Cylinder, upgraded calipers and rotors, brake cable, drums and all internal parts at the rear. No improvement. I even replaced nearly all the lines. Finally, I decided to measure the push-rod length to master cylinder play. It was over 1/2" with all new parts. Apparently the new boosters ship with the push rod screwed all the way in. I matched my new length to what I took out, but apparently that was also incorrect. With the little $20 tool for eBay, I was able to measure the endplay between the Booster and MC, and lengthen the rod to where there's just a fraction of an inch gap... Once I reassembled, I was able to lock the brakes for the first time. I did notice that the new booster didn't seem to affect anything, and a pumped up pedal didn't move when I started the car. I found the Vacuum check valve nearly blocked, but leaking in both directions. So with a new check valve, I now have AMAZINGLY GOOD brakes for a change. Don't take anything for granted -- but hope this helps someone else. The Push-rod length is adjustable for a reason, and should be checked after either the MC or Booster are replaced or rebuilt. Safety Fast!

 

[Mickey Richaud]

Great tip - thanks for posting, and glad you found the issue!