Brake booster or master cylinder

[Wakko]

Have a 99 limited, trying to diagnose a hard brake pedal. Thought it was the booster so I got that replaced under warranty and it's still giving me the same issue. I don't see any leaks on the master cylinder, anything else I should be checking?

 

[nevada]

Have a 99 limited, trying to diagnose a hard brake pedal. Thought it was the booster so I got that replaced under warranty and it's still giving me the same issue. I don't see any leaks on the master cylinder, anything else I should be checking?

test the vacuum going to the booster. you may need to buy/rent a gauge if you don't already have one.

another test. press the pedal a few times with the engine off to bleed off all the vacuum. then press and hold the pedal when you start it. it should drop .5-.75" once the engine starts.

 

[ambush]

Have a 99 limited, trying to diagnose a hard brake pedal. Thought it was the booster so I got that replaced under warranty and it's still giving me the same issue. I don't see any leaks on the master cylinder, anything else I should be checking?

We need more information. Are the brakes going to the floor, hard brake when pressure build, etc? I too am having an issue after changing booster (2x) and Master Cylinder (2x). Same symptoms of a hard brake aka bad master cylinder.
When I have hard brake, I can fix it by removing the vacuum line for about 3 secs and put back while the engine is on then I have brakes. I do not know what to do at all. It is so annoying that I cannot drive this damn truck just because the ABS system wants to engage on its own.

 

[Wakko]

i think it was a faulty booster that they gave me as a replacement. Went back got another one and it works fine now. I was getting hard pedal all the time, not intermittent.

From the intermittent issues, i think people were saying bad vacuum check valve. Hope you get it fixed!

 

[ambush]

i think it was a faulty booster that they gave me as a replacement. Went back got another one and it works fine now. I was getting hard pedal all the time, not intermittent.

From the intermittent issues, i think people were saying bad vacuum check valve. Hope you get it fixed!

AWESOME you got it fixed. For me, I think it was the combination of me replacing the MC and creating a gasket that goes behind the MC in front of the brake booster. I have BRAKES!!!!!! YES!

 

[SaulG]

Start at 10 rarely is it 9 but possible if it's been replaced