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Unruly brakes

My son’s car, a 1991 Mazda 626 had squeaky brakes; so since he needed a new clutch anyway, he took it to a local mechanic and asked that they look into the problem. He had already determined that the caliper piston in the right front wheel didn?t retract completely and was causing the problem, as the noise would disappear after pushing the piston back manually, at least until the next time he had to brake. The pads were far from being worn out, though he had bought new pads, thinking that the noise was due to worn pads.

The mechanic told me that the problem was a kinked brake line and he replaced it. As long as he was at it, he also replaced the pads, using those that my son gave him. Then he called, saying that he had trouble bleeding the system, and that required a new master cylinder, for which I gave him the go ahead. That should have been it, right? After all, he is the expert.

I picked up the car (my son works nights, sleeps days), drove it for about 10 miles, braking half a dozen times, and the last time I braked, the brakes didn?t release when I let the pedal go. It felt like when you forget the E-brake, and the pedal was rock solid, impossible to push on it. Being almost home, I limped along for a few hundred feet, and when I stopped in the driveway, both front wheels were smoking and stinking. My son took the car a few hours later, and it worked just fine for a few days. But then, the same thing happened to him. We let the car sit for a while, as it seemed to have worked the first time, and sure enough, the brakes released themselves and we drove the car back to the shop. It was after hours, so we just dropped it off. The next morning, I called to explain the symptoms and the mechanic told me that he would look into it. He called me back a couple of hours later and said that he could not reproduce the problem, to come pick up the car. I did and had no trouble reproducing the problem, so the car is back at the shop. I told him that there is no point trying to reproduce the problem, that all that would do is get him stranded a few miles away with no way to diagnose anything, and that in my opinion, my description of what happens should be sufficient to start troubleshooting.

Question 1: Am I right regarding the need to reproduce the problem?

Question 2: What could he possibly have done wrong when he fixed the brakes the first time?

Question 3: Isn?t there an obvious potential cause of the problem to troubleshoot first?

Thanks

Fraps1

All that’s left that could cause this problem is the brake vacuum booster.

One thing that can cause this problem are deteriorated flexible brake hoses to the front calipers. These hoses can deteriorate internally where pieces of rubber can delaminate from the outer lining of the hose and act like a check valve. That is, it allows the hydrualic pressure to applied to the caliper pistons when the brakes are applied, but when the brakes are released this check valve action of the deteriorated rubber prevents the hydraulic pressure from being released from the caliper pistons. So the brakes remain applied.

Tester

Thanks Tester.
However, how do you explain that the brakes are applied to both wheels while at least one brake line was replaced?

You said he replaced a kinked brake line. A brake line is a metal portion of the brake system and can be kinked. A brake hose however cannot be kinked as it’s a flexible portion of the brake system. Contact the mechanic and ask what kinked brake line was replaced, and if there was anything done as to the brake hoses.

Tester

Good point, Tester. But I just checked and I found 2 errors in my first post:
1- They did put 2 new brakes hoses in in addition to the kinked line.
2- They did not replace the brakes master cylinder, I got confused because they replaced the clutch master cylinder.
What’s the next step? What’s the next probable cause? Isn’t strange that this would happen after they fixed the brakes? All my son wanted was to fix the squeaking!

“What’s the next step?”

Master cylinder. My post at the top assumed the brake master cylinder was replaced.

I read your post and something flashed,is it possible that some contaminated brake fluid was used (like the mechanic finished off a already opened can that really wasn’t brake fluid, I know it’s a long shot).