I have a 1992 Honda Accord LX 4-dr sedan with 191,000 miles on it. I am having an issue that I SUSPECT is a Master Cylinder problem but I'm not sure. When braking, especially while stopped, like at a red light, the pedal slowly sinks to the floor. I can pump it right back up but with pressure on it it slowly goes down again. This is really prevalent in hot weather. In cold weather (I'm in Michigan) when the air is dense, this does not occur. I find no brake fluid leaking on the garage floor or there is no indication of leakage at the wheel hub.

Is this a problem of the Master cylinder? I have had some suggest the rear brake shoes (not disc pads) need replacement, indicating the shoes are worn thus leaving nothing for them to press against, not reaching the brake drum when the pedal is depressed.

I would appreciate any advice.

This is my first posting. I'm new to posting on a forum so I hope I did everything correctly!

Thank you,
Dennis

 

G'day Dennis,
Your instincts are on the money, the problem is indeed the MC, or at least the symptome strongly suggest so.

The MC has in effect two cylinders inside each opeating a seperate hydraulic circuit, one circuit operates the right front and left rear brakes, the other operates the left front and right rear brakes.

One of the seals for one of these circuits is leaking pressure, and the pedal slowly loses height as a result. As the pressure leaks past the seal, fluid leaks back into the reseviour, thus there are no external signs of leakage and the fluid level remains constant. You need a new MC, it is potentially dangerous.

My car has a similar problem, but only in hot weather, which I assume must be to do with the flexibility of the piston seals at differing temperatures. I'ts winter here now, so I probably won't fix the problem until the weather starts to warm up.

 

Thank you for confirming my suspicions. I guess I'll be looking for a Master Cylinder. I'll be searching for a post that will help me replace that...doing the work myself. Thanks again.

 

It's not hard to change a master cylinder, you just have to be gentle/careful with the brake lines. The new master cylinder should come with directions on how to bench bleed it. If you do it right, you probably will not have to bleed the brakes too. Good luck.

 

Thank you for that information. Any tips on where to purchase one? I see them on-line but wonder if my local auto parts store will have them??