K3500 Brake Problems

[Jackedup86GMC]

Most times my brakes work great. However, sometimes after I have stopped, then started to move again, the pedal is really spongy and I have to pump the brakes 2 or 3 times before the pedal feels normal agian. I have no evidence of fluid loss anywhere on the truck. Is this maybe a vacuum problem related to the power booster? Any ideas?

 

[bigred81]

Check the rear wheel cylinders they will let air get in the system also the master cylinder may be leaking to the inside of the booster I have had this happen. The seals in the master my be going bad that sound alot like the seals. Normally what happens is one section of the master will bypass or it is sucking air in the back of the master cylinder I have seen all these happen at the shop. From what you are saying it sounds mostly like a bad master get a rebuilt or new master andd this should solve your problem.

bigred81

 

[Confedneck79K30]

pull the master off the booster with the lines still connected, and stick a rolled up piece of paper down towards the bottom of the master and look for signs of wetness on the paper, if there's wetness, you know its leaking into the booster... if not, check the rear wheels for wetness behind the drums...