Hello there. Any thoughts/suggestions would be greatly appreciated.

I have an '86 Z28, 305ci. auto. 4 wheel disc brakes. Bone stock. about 90k miles. Gets driven pretty rarely. A troubling and dangerous problem has started happening lately. The brake pedal goes soft on me. Very soft. So far only at idle speeds or going slow, like in driveways or parking lots. Sometimes it doesn't go all the way to the floor and if I pump it a couple times it comes back to life and I can stop the car but a few times recently it went all the way to the floor and attempting to pump the pedal did nothing. In a moment of panic while slowly closing in on the car in front of me I have had to rip the parking brake or jam it into park. But then after revving the motor and letting the pedal rise back up it is ok again.

I'm freaked out about it now and do not want to drive the car until I get it addressed. There are no fluid leaks that I can see. The fluid is full and looks good. It probably hasn't been flushed ever other than for one brake job the car has had in 25 years which was at least 15 years ago. My dad owned the car before me and I know the master cylinder died on him and spewed fluid everywhere...when the car was only 4-5 years old...it was replaced then.

I was going to start out by opening the lines and bleeding it all the way out and refilling the system.

Any other ideas you guys out there with Camaros may have for me?

Thanks.

 

Brake booster?

 

Or, the line supplying the booster with vacuum is disconnected or cracked.

 

Considering how long it's been sitting, I think that's a very good start. Suck/remove (I use a big syringe) the old fluid out of the reservoir and refill with new before you start bleeding it. Also, a master cylinder can leak internally and not show anything externally. See what bleeding the lines gets you first. As far as it being the booster, if it was bad or if you had a vacuum leak, the pedal would be stiff. The pedal dropping to the floor like it's doing to you is a hydraulic issue. (not tryin to pick on ya dj)!

 

More than likely the master if he has no visible leaks. If fluid level is OK then master is leaking internally.
Never throw it in PARK to STOP, unless you don't mind replacing trans. Low gear and park brake.

 

The hose leading to the booster from the manifold/plenum seems perfectly ok...good as new. So it is the master rather than the booster? That is good news as far as replacement goes, I suppose. Anybody tried a master cylinder replacement job? Is it a pretty straight forward job? Sorta looks like it. I have manuals...just haven't looked at them yet

What troubles me the most is that it works fine and then out of the blue the pedal mushes to the floor like it does. Sometimes when the car is cold and sometimes when it is hot and has been running for awhile. No rhyme or reason or pattern to it. If there was a vacuum leak or if the master was out and out shot I would expect the pedal to be mushy all the time.

 

One more thing if I may....some clarification please on what you meant when you said the master cylinder is leaking internally. This is what I am seeing in my head....When I push the pedal brake fluid is escaping past the pressure seals and bubbling back up into the master cylinder well? So the pressure in the lines drops and the pedal mushes to the floor, yes? This makes sense to me and tells me that a master replacement is what's called for. I'm capable with a wrench. I've done plenty of work on this sled and I've even pulled the intake manifold off this car to fix a manifold bolt/water jacket leak and managed not to F that up so I think I can handle this, yes? I've got time to figure it out because it is 90 degrees outside. No hurry.

 

You got it. So you're going to assume it's the master and not just a needed bleed job? I guess, considering the age and miles, replacing the master probably won't be a waste of time and money in the long run. And the hit & miss you're experiencing, I've had that with a bad master cylinder. But, I've also had that with a bad brake caliper that was leaking by internally, no external leaks.

 

one of the valves in the master cylinder is sticking and needs to be replaced. follow the directions on bench bleeding before replacing it

 

Thanks for the input, guys. Yeah...I don't know...I was gonna do the bleed first but something tells me it's more than that...A mechanical thing with the master cylinder seals and a valve sticking, like microkid said. Think I'll replace the cylinder while I'm at it. Thanks for the advice about bench bleeding the new one. I might not have known to do that. Anyway why not replace...should be less than $100. Maybe in September when it stops being so stinking hot outside in the garage. Thanks again!