Went for a ride today brakes worked just fine when I left. About half way through the ride my brake pedal went real soft, the only way it would stop was at the floor. Limped it home and noticed when I pumped it with the engine off after the first pump the pedal would get hard, so I dont think the MC is bad. Also MC bottles are full of fluid, so its not low on fluid.

Any help would be appriciated...Thanks Jim

 

Check the back side of your tires and wheels for signs of brake fluid. It doesn't have to leak much to make the pedal go to the floor. Sounds like a leaking caliper to me.

I just put a pair of Wagner Quick-Stop loaded calipers on my '71 2 days ago. Similar symptoms, and it turned out my LF caliper was the culprit.

Good Luck.

 

Ok, I checked for any leaks and found none. I checked all four calibers and abs system and followed all the brake lines. Now heres the weird part cars been parked in the garage now for about 2 hours and it has cooled down so I start the car again and check too see if there's any difference and now the brakes work and feel just fine. So I'm guessing I need to replace my brake fluid with new. Now then what does everone recommend using. It's a 90 if that makes any difference.

 

What happens if you step hard on the brake and keep your foot down hard? Does is slowly move toward the floor? Usually a MC on the way out can be temporarily made to work by pumping.

 

Sounds like Air in the system, either lines, MC, booster, I'd do a complete power flush....

 

Well after my reply at 4:00 I decided to run by oriellys and pick up some brake fluid and a hand vacuum pump and while i was there I talked to one of the workers and he said it sounded more like the booster was bad but couldnt be sure because of how after I let it sit for awhile how the brakes started working just fine. So i deceided to just wait and see if it does it again. They feel just fine now. I'm really confused.

 

Had the same very strange thing happen to me last year on my '92...brakes went all the way to the floor, out of nowhere, on my way home from work...Next day, they were working fine...WTF? Scared me enough that I took the car in to have it checked out (to the local GM Stealer)...they told me that they couldn't find the problem, but that there is an adjustment rod in between the MC and the booster that could need an adjustment. Had them check and adjust, and have not had a problem since...Maybe something to look into.

 

I posted this a few weeks ago to no avail - same problem you are having or close to it. I think the fuse I pulled under the hood was actually the ASR fuse (real large one) and my ASR light is on. I would be careful - my brakes went out numerous times in precarious situations.

1994 Corvette Convertible stock - I posted a message a few years ago about my brake problem which has never been resolved. I pulled the ABS fuse from under the hood and have not had the problem since - of course I don’t have ABS or Traction control now. The problem is this - while driving straight and level down the freeway I went to exit and applied my brakes which went to the floor with no resistance and the engine shut down and all my dashboard lights came on. I restarted the car and limped home using my hand brake. The next day the brakes worked fine and continued working for a few days then the same thing happened - brake pedal to floor but the car did NOT shut off. I replaced the Master cylinder 3 times, the pump once and had the system bled numerous times but the problem was still there. Every once in a while the pedal would go to the floor - get a little paranoid never knowing when your brakes are going to have a complete failure. My mechanic and I assumed it may be the ABS so I pulled the fuse and in two years have not lost my brakes but it sucks without ABS and traction control. It takes forever to stop. The local Chevrolet dealer and the factory rep told me it is a 1 in a million chance the ABS could cause a complete brake failure. Any ideas - thanks in advance for your help.

 

Sounds more like a bad master cylinder than a booster, a bad booster will make the pedal hard not soft.

 

Buy a large can/bottle of Valvoline supersyn. Its clear and priced well. Replace your bleeders with "Speedbleeders". They make the job fast and easy.

 

I have a '90 also and the exact same symptoms happened to me not too long ago. Most likely its an internal leak in MC, but there's a couple of possibilities after you checked what you did.
Do the pump test with the engine off and pump the brake pedal about 10 or 15 times. Do this right after the engine's been shut off. Look at both: the level of fluid and what's in the fluid. Does it look completely clear, aside from some yellowish or amber coloring? When my master cylinder went, the same **** was happening at first, I didn't notice any lowering of fluids. Soon though, I noticed small clouds of crap were being pumped from the bottom of the cylinder cups(check both) into the fluid, undoubtedly due to the fluid exchange through leaking seals as the internal seals were worn inside the master cylinder itself. They gave the illusionary effects that there was a leak somewhere else in the brake line. I even went and replaced the fluid and did a flush just to be sure, but obviously to no avail. If it acts completely erratic like that, odds are it's something internal in the MC starting to go. And if it is, obviously it needs to be replaced/fixed asap. One other slim possibility is that your MC pushrod was misadjusted. I know this may be an offshoot, but it happened to me a few months ago when my MC went out so I'm listing it. If someone recently did your brakes or messed with em, your pushrod may have been thrown off in these C4s. My past mechanic used the wrong size bolts/screws on the pushrod assembly and it took a further decrease for the brake pedal before it was braking correctly, so this may be your problem, or atleast part of it. Have it checked and adjusted if needed regardless of what you hear. I had 3 dumbf*** mechanics basically try to tell me it was bs until I found one that told me I was right on a c4. However improbable, it's not impossible.

BTW: If it was the PBB, the opposite would be happening: ie: the brake pedal becomes a serious BEEEYOTCH with you on the road just to stop the car...acting rock solid to the touch and refusing to go down easy. Trust me, you'll know if its your PBB when your braking foot becomes numb from the strain. I had that happen too, but way before this.

 

 

Thanks for all the reply's guy's. I'll check into the MC alittle closer.

Jim

 

I had the same symptoms today on the highway with my '85. But when I got home I found that the rear plastic cup was empty and there was fluid running in between the master cylinder and the booster.

Bad MC?

Can you get rebuild kits for them?

 

I don't think you can get rebuild kits for them. I just replaced mine and everything is fine now. I got a rebuilt one for $71.00 from my local auto parts store.

 

There are rebuild kits. There are also new seals for those cups of fluid. I'd put in the dougrippie.com brake bias spring while I was working on the M/C. $71 for a rebuilt is a sweet deal! If the cup was empty, you might just need to fix the seal.

 

I looked closer and found that under the reservoir in question it was quite moist and "clean". I wiggled the cup after I refilled it and I could get moisture to come out of the rubber grommet in the bottom.

Off to NAPA tomorrow to explore the options.

I will keep you guys informed. Thanks!

 

Your reservoir seals aren't leaking, that won't cause your symptoms.

Your master cylinder is leaking internally. When you push the pedal, fluid shoots past the seal and up into the reservoir. If it doesn't blow the cap off, it'll spray everything and then get past the cap and run down the side of the reservoir.

M/Cs can leak intermittently, quit driving it and fix it as if your life depended on it.

 

Yes.

No. Even if you do find a rebuilt kit, that only replaces the orings, it doesn't replace the scratched up / pitted / corroded aluminum bore of your master cylinder.

 

Central C...


...your exactly right. I just thought I would try the 5 dollar option first, and I didn't even get backed down the driveway and I realized that isn't the issue.

Looks like its the $80 reman from NAPA for me. Also ought to be a bleeder so I don't have to use a hose and a Sprite bottle.

Everyone, thanks for your help!