Slowly Losing Brakes

[berky2500]

Last Thursday, my brake pedal went to the floor with almost no pressure, not cool. I let off the pedal and pressed again, full pressure, normal brake.

I've driven it a few more times and each time it gets worse, meaning it takes more pumps of the pedal to get pressure, usually the first time the brake light on the dash comes on, once I get pressure, the light on the dash goes out. I've looked at all four wheels and the master cylinder at least three times, as well as the reservoir cups. I can't find any evidence of leakage anywhere.

I'm leaning towards internal leakage in the master cylinder. But I'm not 100% sure that I don't have a vacuum problem. I've had a vacuum booster fail on my truck before. It was easy to diagnose, I had no power assist and had to stand on the brakes to stop. I've pulled the vacuum hose out slightly and seem to have vacuum there.

This time, the pedal goes completely to the floor with almost no pressure, then the 3rd or 4th time I get hard pressure and it will hold until I let off the pedal. Another strange thing, sitting in the garage level, in park, I get full pressure almost every time. Driving the car, not at all the first or second time.

Can anyone confirm my suspicions about the master cylinder?

 

[ffvetteman]

I just replaced my master cylinder but for a diferent reason. Mine was taking fluid from the rear resovior and filling the front.

But...I think it my have something to do with it but I would check ALL the lines all the way down the car. Let the car sit inside for a few days (to make sure the underside is dry) and follow the brake lines carefully for ANY moisture. One may be cracked or a rubber line may be leaking a very little bit.


Good luck and keep us posted!!!

 

[Magmotor]

I just replaced the booster on my '89. Everytime I hit the brakes I heard a hissing noise and the brakes went to the floor. I still had brakes but they were very hard and didn't grab untill one inch off the floor. Do you know if the master & booster are original?? If so I'd go ahead and replace both. GM wants over $400 for the booster.....way too much...I got mine at Advance Auto for $131 and a life time warrenty. One word tho: It is a royal PITA to replace the booster. The right stud coming thru the firewall is nearly imposible to get at. You need a 1/4" drive w/two swevels on it to get to it. Also you need someone to hold the booster while you put the nut on or it will just push back out thru the firewall. I used a 2x4 to wedge it againts the block and the booster to hold it. Took me 5 hrs and many cuss words. If you replace the booster be SURE to adjust the new rod to the EXACT LENGTH as the one you took off. At least to 1/16". When your finished make sure your brake switch & auto cruise control vacumn switch are back in the original position. They can easly be pushed back and your brake lights will remain on no matter what and the cruise control won't work. Bleed the Master Cy while out of the car then when back in place the only bleeding that needs to be done are at the two lines comming into it. Good luck with it..!!

 

[c4ever]

I had a similar problem not long ago. New master cured it.

Carlo

 

[berky2500]

I'm guessing that they are both are original, only because they say Girlock on them. But truthfully, I'm not sure. There have been many strange and broken things found on my car so I'm not sure what is original and what is not.

The car is nearing the scary stage, but I'm in the middle of a drum to disc conversion on the back of my truck. As soon as it is back together, they will swap places in the garage and I'll tear into this and fix it. Barring finding any actual leakage (haven't so far), I'll start with the master cylinder and go from there.

Thanks for the input, I'll let you know what ends up fixing it.

 

[atmmac]

Definetly your master cylinder ive experienced it first hand on my impala.

 

[tyrel]

Yes, it certainly sounds like your master cylinder, which is so easy to replace that it's not funny. Just be sure to bench-bleed your new m/c before installing, and then of course bleed your whole brake system after installation.

As MagMotor says, in the event that your booster is also going south, it is very difficult to replace. I removed the drivers seat and lay down, on my back, with my legs moving in all directions as I tried to tighten the booster to the firewall. You can make the job go faster by swearing.

 

[berky2500]

Five votes for the master cylinder, all this technical help can't be beat. I already know about the power booster, I did the one on my truck. It's a full size, extended cab, 3/4 ton, plenty of room except that two of the nuts are under the steering column support making them near impossible to get your hands in.

I would add that in addition to copious amounts of swearing, a fair amount of blood has to be spilled from your knuckles to get these blasted things back in. I'm trying to avoid the vaccum booster if at all possible.

I'm pretty sure that the vacuum booster is the second thing mounted to the firewall during Corvette assembly, right after the heater core. :bash