Brakes, master cylinder problems?

[cantthinkof1]

I have a 1992 Ciera S and until recently the brakes worked fine. About 3 months ago I decided to replace the rear brakes because the brake pedal was almost down to floor. After the rear brakes were replaced, only the shoes were replaced as the drums were OK and machined properly, the pedal was back up again and stopping was normal. Soon after, about a month later, the brake system started showing problems.

Everytime I would stop and then release the brake pedal I would get a "clunk", some kind of a clamping noise, from the rear left brake. On top of this problem, the brake pedal is now more down when you press it than it was after I replaced the rear brakes. A relative of mine told me I may need to replace the master cylinder. I, on the other hand, think that something else could be the problem, such as defective shoes or maybe something got loose. Either way the car stops but not as optimal as it should.

I checked the brake fluid and it's OK. The mechanic filled it up all the way to the top when he did the rear brakes. The fluid level right now is almost at the top and there doesn't appear to be a leak in the brake line.

Does anyone know what's going on? What are the symptoms of the master cylinder not working? I would think such a simple thing would either work or won't work.

[GTP Dad]

There may be a couple of simple explanations to your problem. First, have you bled the brakes recently. This problem sounds to me like there is air in the system. Air in the system will cause the brake pedal to be mushy or as you describe go to the floor. It doesn't matter how much fluid there is in the system if there is air in the system it will not allow the fluid to flow properly and give the symptoms you describe. If you haven't done this before it isn't difficult to do and they even sell one person bleeding systems at most parts stores. Second are the rear brakes properly adjusted. If they aren't this could account for you having to move the pedal further to get them to engage. The wheel cylinders can only expand the brakes so far and if they are too far out of adjustment you may experience a problem. Finally, most master cylinders when they go bad either leak or the pedal will go all the way to the floor. You can usually pump the pedal to get brakes but you would have far worse symptoms than you describe. Before you replace the master cylinder, check the entire system for leaks, and then bleed the brakes. I think this will solve your problem. Good Luck!

[cantthinkof1]

Thanks GTP Dad. I was quite sure if it was the master cylinder I probably wouldn't even be able to drive the car. Yes, the mechanic did bleed the brakes when he put the new ones on, and according to my relative, who's the one who took the car to the mechanic, he also adjusted everything properly. Perhaps something is wrong with the shoes themselves.

[GTP Dad]

That is always possible but the spongy brake pedal still leads me to believe that there is still air in the system. I had a car once that had the brakes redone, they worked fine for a day and the pedal became very weak and spongy. Took it back, they rebled the brakes and everything was fine from that point on. Let me know what you actually find the problem was.

[cantthinkof1]

I will and thank you for the advice. I'll tell him to re-check all the springs and shoes and re-bleed the brakes and hopefully this will fix the problem.