Car Guys/Mechanics, I Need Your Help

[Mike]

I have an '85 6000 STE with the four way disc brakes {don't laugh, its all I can afford right now}. So, about a week ago I notice that the brakes feel "different" when I run up to the corner gas station. At first I chaulk it up to wearing different shoes than I have been wearing all summer. The next day I run out to the store and when I get close the pedal goes to the floor, the brake light comes on and it takes longer to stop. "crap" I think, "must've broke a brake line." I park on a clean spot in the parking lot and go do my shopping since I'm there. When I come out, there are no puddles. I check the master cylinder reservoir- full. I limp home and consult with my dad and my neighbor, who knows a bit about brakes. The conclusion is that the master cylinder is bad.

So, i replace it, bench bleeding it and bleeding the system. Take it out for a drive and the same thing still happens- Brakes catch, but the pedal goes way down, brake warning light comes on. We rebleed the master cylinder, since we had some issues doing it the first time and rebleed the system again. Again, same problem. What the hell is going on here?

One thing too, and perhaps this is the problem{?}- when we went to bleed the rear, driver's side brake, the caliper and rotor were really rusty, almost like it wasn't even working. After bleeding that side, and holding the pedal down the brake caught, so now it appears that the brake there is working. Could this weird caliper/rotor thing be the problem altogether? Could there just be more air in the system and another rebleed of it be in order {which I'm going to do later once I can get an assistant}? Is it something else entirely and I'm wasting time and money?

I'm at a loss here. We've done everything, taken our time and still the brakes don't work right. They do catch but the pedal goes way down, and the signal light comes on. If you pump the pedal, like at the stop sign at the corner, it does built up pressure and seems to act normally, but moving and stopping further up the whole thing starts over again. Luckly, my mother's been in florida for the past week so I can use her car to get around, but she comes back tonight so that's going to end.

 

[j]

It sounds like you need to flush and totally bleed the whole system before you'll know what the problem is. If you can find someone with a vacuum bleeder it will go a lot faster. Obviously, be sure to check that the reservoir never gets low while doing that. It's possible that there was just so much air in the line that the rear brake wasn't even getting pressure. Also, be sure to check all the lines for kinks or leaks etc that could be introducing air into the system.

 

[texas_jack]

Maybe the fluid is draining into the powerbreak housing at the back of the master cylinder.

 

[texas_jack]

Oooo, wait, I have an idea. Maybe a line is swelling. The rubber that they use at the four corners maybe swelling when you step on the brake. have someone watch each line when you step in the break

 

[Thomas]

Originally Posted by texas_jack

Oooo, wait, I have an idea. Maybe a line is swelling. The rubber that they use at the four corners maybe swelling when you step on the brake. have someone watch each line when you step in the break

Good call. Car's over 20 years old and those rubber pieces might be on their last legs.

 

[Dmax]

Mostly likely you are not bleeding the system of air properly, like J suggested. Other things to check: power brake booster pump, seized calipers and rubber brake lines next to calipers, as Jack suggested. If you purchased a rebuilt master cylinder there is a chance it may be defective.

 

[dah328]

Classic dead master cylinder symptoms. You won't see external leaking of brake fluid as the leak is internal to the master cylinder. In other words, the internal O-rings in the master cylinder are shot and not holding the hydraulic pressure constant which is why your brake pedal is sinking to the floor and why pumping quickly results in some restoration of pressure. Bleeding the brake lines doesn't do anything because the master cylinder doesn't hold pressure regardless of whether it's new brake fluid or not.

 

[j]

^^ You think the new one is dead too? There must be a way to test it by plugging the output and pumping it, right? I could see this being possible, but does seem unlikely to me.

 

[dah328]

Originally Posted by j

^^ You think the new one is dead too? There must be a way to test it by plugging the output and pumping it, right? I could see this being possible, but does seem unlikely to me.
Oops, I completely missed the part where he replaced the original master cylinder. I would think it unlikely although not impossible that the replacement was bad. I don't know if there are other components in the system such as a brake booster as Dmax mentioned, but that could also be the problem. The symptoms don't seem to indicate either swelling brake lines or a seized caliper although the calipers are easy to check.

 

[texas_jack]

Originally Posted by dah328

Oops, I completely missed the part where he replaced the original master cylinder. I would think it unlikely although not impossible that the replacement was bad. I don't know if there are other components in the system such as a brake booster as Dmax mentioned, but that could also be the problem. The symptoms don't seem to indicate either swelling brake lines or a seized caliper although the calipers are easy to check.

It's happened to me. I had a bad mastercylinder and the refurbished one I got at Autozone was bad too.

 

[dah328]

Another thing -- you can damage a master cylinder if you're manually bleeding it and you let the reservoir run dry, so if that happened at any point during the trouble you had bleeding it the first time, there's a greater chance it's bad. I would also double-check that rusty caliper on the left rear. Is the piston rust-free and operational? Does it easily clamp on the rotor and easily release it?

 

[Mike]

Well, I'm working on replacing the one caliper. Even if it turns out its not the problem, it needs to be replaced anyway, preferably before winter. So, I have the parts on order at the auto parts store.

My sister's boyfriend let me borrow his vacuum bleeder so I'll try that, but my old man's been working on cars for like 35 years so we were bleeding the system right.

Other than that, if its still acting up, I'm guessing it could be the booster. Any tests you can do on those things to make sure they're on the up and up? Either that or I got a crap replacement master cylinder, but how the hell can you prove that to get a replacement?

Thanks for the help from everyone though. This things been pissing me off for 2 weeks now, and some new ways of thinking about it is appreciated.

 

[Mike]

Finally replaced the rear caliper, rotor and pads, which was a trip {rotor was wrong- didn't fit over the hub, and it looked like the factory just didn't lathe out the inside. So of course the store had to order a new one that took 2 days to get}. Bled it, still have issues. Brake pedal goes all the way down, brake light comes on, if I pump them it builds up pressure and seems good until attempting to stop again. So, I'm lost. Air still in the system? Just got a ****** replacement master cylinder to begin with? Something else?

 

[Thomas]

I'd try another master cylinder at this point and re-bleed. Sucks to have something like this drag on like that.