| Subject: | Vanishing brakes |
| Question: | Hi! I'm driving an '92 Mitsubishi eclipse. An older car, but basically still a reliable beast. Until recently that is. The Brakes will go out suddenly. There will be no warning. One minute you'll have a firm pedal, and the next it will touch the floor boards. There's just a touch of brakes down there... enough to slow, and it feels like only one of the rear brakes is engaging: it wants to pull to the right. Two minutes later though, you'll have pressure again, and things will work fine. This has happened twice now... with great amounts of time in between the two instances. The first time, I pulled over IMMIDIATLY, and called for a tow. The Mitsubishi dealership garage couldn't find anything wrong with it though. They changed the fluid. Told me they had run every diagnostic, and it must have been a fluke. (Or my imagination, that was implied: "are you sure you weren't pushing in the clutch?" Since it's not my regular car, and the owner didn't want to push... I couldn't really do anything. I spent the next month and a half or so driving the thing with one hand on the emergency Brake, and a cell phone handy. And just about the time I had started to relax: It pulled the same thing: A sudden failure (While in motion) the brake pedal hit the floor, and there was just that feeling of barely engaging brakes... no pressure. Ten minutes later I had pressure, and everything was fine. I'm hoping you have some clue... or can point me in the direction of someone who might.. This is a VERY strange problem. Will |
| Answer: | Will, This is a strange problem, but not unheard of. The dealership can run all the diagnostics in the world and not find the problem I'm thinking of because it's not hooked up to any sensors. My guess is that your Master Cylinder is the problem. Your master cylinder contains two springs and two pistons that when compressed, force the brake fluid through the brake lines, which in turn make your brake pads/shoe push against your discs/drums. It sounds like in your problem that one of the springs in the master cylinder "collapsed" for some reason. If that spring looses it's compression, you'll have to push the brake pedal all the way to floor in order to get the car to brake at all. That car would need to have it's master cylinder replaced if that is truly the problem. Another guess I have is that the brake booster (sometimes call the vacuum boost) is not acting correctly. Basically, the booster amplifies the force your foot puts on the brake pedal and that inturn is responsible for compressing the pisons and springs in your master cylinder. If the booster is not functioning correctly, or its check valve is not working right, you will indeed need to press the brake pedal all the way to the floor to get braking done. I can't imagine what the "diagnostics" were that the Mitsu
dealership performed, but I would guess that it was not thorough
enough. If you don't feel confident with Mitsu's answers (I know
I wouldn't) take the car to a brake shop (the braking system is very
common on the Eclipse) and have them take a look at it. If you take
it to another repair shop, ask them to specifically inspect the master
cylinder and the vacuum booster. Also tell them your story. They
will not waste time looking at other brake parts and doing the same "diagnostics" that
Mitsu did. You will give them something better to focus on. |