Evil.Dingo

I searched before posting this and found some stuff but still wanted aditional input. Ok so heres the problem: Brakes are mushy and loose pressure while holding them depressed at lights and under one push stopping (pressing the brake without pumping). If you pump the brakes they hold but according to the tech manual, the test procedure to see if your brake booster is bad is with car running pump and hold brake pedal, turn off ignition while holding brake, there should be no loss of brake pressure for 30 seconds. I tried this and it holds pressure 2 out of 3 times. The one time it does not hold: counted to 20 seconds then the brake slowly made its way to the floor.

This makes me assume its the brake booster. BUT I found in my searches that a bad master cylinder can cause the same problem due to the seals not holding. I ordered a new 1" bore master from 4wheelonline since the one in the truck has never been replaced. Do you think my problem could be a master or is more than likely the booster. I have to wait until my master cyclinder arrives to test but I was thinking maybe I should order a booster as well. Is there a average life expectancy on the boosters?

desconhecido

Sounds like you have air in your brake fluid. Bleed the entire system well and carefully before you mess with the booster.

There have been a couple threads here recently where people spent a whole lot of time troubleshooting the brake system, including multiple master cylinder replacements, and concluded that the problem was with the brake booster. So, it's possible that the problem is with your booster. But, the vast majority of times that symptoms such as yours occur, it's master cylinder, wheel cylinders, caliper cylinders, soft lines, or connections. Also, could be the LSPV, though I think this is rare, too.

Evil.Dingo

Thanks !

abecedarian

If you can't hold brake pressure, it's likely the master cylinder... but could be a wheel cylinder or caliper bleeding down, but if you don't have fluid leaks at the corners, that's not the problem.
Even if it were the booster leaking, as the vacuum in the booster leaks out, it makes the pedal more firm.