JohnnyLT1Runner

I had parked the car for about an hour and started it up. The brake pedal didn't seem to go all the way down and stopped hard like something was blocking it. Braking power was very weak.There was also a hissing sound when I pressed down on it like some sort of vacuum leak.
I honestly have no idea what would suddenly cause the brakes to mess up like this. The Master cylinder is a remanufactured one that I put on several months back, could it suddenly go out like that?

Kmcoldcars

What you describe sounds like a vacuum booster. They are famous for cracking. Always include the year of the car in the question as they are not all the same. If you let people know where you live you may very well find offers of people willing to come over and help fix the car.

JohnnyLT1Runner

I was thinking it might have been the brake booster from the noise, but I didn't have any Idea they could crack like that.
The car is a 91 L98 Auto Coupe. Forgot this time. I have no problems with repairing it myself, this vette just always gives me stupid problems that I have never run into with other SBC vehicles.

Aqualoo

Check the hose coming out of the booster

JohnnyLT1Runner

I've been reading through all the old threads and I will check the hose first and then the booster for cracks. Everything I'm reading sounds just like my problems and it's either the brake booster or hose.
I should mention that there is a hard line coming off the intake to go the booster instead of a soft line, is that normal?

JohnnyLT1Runner

I got like 30 seconds yesterday to look at it. I can't believe I didn't remember this, but it has a steel Brake Booster. So that's not the problem. I didn't really look the hose over real well, but it can't be much else right?
Also, my HVAC hasn't really been wanting to change vent settings so that vacuum line may be an extra symptom, If I knew where it's located. I don't have a 3 way vacuum hook up to the brake booster, so, anyone have any ideas?

94z07fx3

Steel shell not withstanding it still sounds like the booster. Inside the steel shell is a check valve and diaphragm that are rubber-like and fail. Do you have a vacuum pump? If so rig up a line in place of the one from the intake and see if it holds vacuum. Or listen to the booster at idle then disconnect and plug the vacuum line and listen again. Any change?

....Other issue....

Follow the vacuum line from the cruise control module and it eventually will lead you to the line that powers the air blend door.

JohnnyLT1Runner

I will check that out. Additionally, the cruise has never worked since I've owned the car. It wasn't a big concern compared to fixing other neglected things at the time. I'll hunt that down and see if everything is connected to the same problem.

Cliff Harris

Sounds like a ruptured brake booster diaphragm.

Cruise control not working is usually the vacuum check valve next to the distributor. They are roughly $3 at any auto parts store, brand not important This is the guy:



The hose going off to the right and upward goes to the HVAC vacuum system in the cockpit. The hose going off toward the bottom goes to the cruise control. There is also a cruise control vacuum switch involved, mounted on the brake pedal.

JohnnyLT1Runner

Got a few minutes to test it out this morning. It is definitely the booster. It's odd to me though that it is steel, and it has a 1/8 th inch billet spacer behind it.

jhammons01

^^The Diaphragm is plastic....

The '84 Booster had a steel Diaphragm....later years got a plastic diaphragm "inside"