1997 Z71 brake problems

[79403ta]

Hi all its been a while since i have been on here but i will get to the point...tuesday evening i was driving home from work in my 1997 Z71 with a 5.7 and when i went to stop my brake pedal got real hard (kinda like a truck w/o power brakes) and my rpms died way down to about 400 rpm almost stalling but when i let up on the brake pedal it was fine again...i am wondering brake booster or master cylinder ??? and i know these trucks are bad about intake leaks would this affect the brakes like this....the truck runs perfect until you mash the brake pedal the it acts like it sucks the vacuum out of the motor and tries to stall....also if you keep the pedal pushed it will hiss loudly like air is leaking down by the pedal (i am used to the hiss when you first push the pedal but this dont quit until you release it) it really acts like a vacuum leak or something simular...i pulled the check valve out of the booster and it is getting great vacuum there sorry so long just tring to get everything out here thanks for any help Jason

[SpitAndDirt]

Ok....I had a problem very similar to yours on my 96 Z71 and it ended up NOT being my brake booster, but very close to it. Ok, you need to remove the two nuts that hold your master cylinder to the brake booster. You will NOT need to remove the steel lines, you only need about 2 inches of clearance to get your fingers in the hole. I developed a leak from the rubber gasket that sits behind the master cylinder in the booster. It is supposed to be greased so that the constant friction of the plastic and metal pushrod assembly doesn't tear it. If that gasket is ripped in any way, cheapest way to fix it is to go to the junkyard and find one. Be sure to grease the plastic and the seal with some petrolium jelly when re-installing for lubrication and sealing.

Before you go and buy a brake booster, plug your Booster vaccum line off and drive the truck slowly around the neighborhood to double check that the problem stems from the booster leaking "false" air into the motor.

Otherwise if your seal is not bad you pretty much end up with a internally leaking brake booster. There's not much to them really, but the parts stores love to rape you on the price. Good Luck -Chris