[biggychase]

I've tried posting this in the brakes forum with no success, so I figured someone here may be able to help.

I recently replaced my MC as my pedal was sinking to the floor under pressure. After I intstalled it and bled the system (I've bled it 3 times now, absolutely no air in the lines), i tested it out, and the brakes lock up after about 5 minutes of driving. The brakes lights are on, and it takes about an hour for the system to depressurize. Could I have a problem with my booster? What about the rod that goes from the pedal through the booster and into the MC?
Please let me know what you think the problem might be. Any advice at all would help!
Thanks



[Modified by biggychase, 5:20 PM 4-5-2002]

 

[tornadoredcabby]

Re: Brakes stuck on... please help (biggychase)

Bump...

 

[VWtub]

Re: Brakes stuck on... please help (tornadoredcabby)

 

[WackyWabbitRacer]

Re: Brakes stuck on... please help (VWtub)

The Master Cylinder pistons are not returning correctly, possibly due to a defective brake booster. As you know, the brake booster uses engine manifold vacuum and atmospheric pressure to provide assistance to the braking system.
You might want to check the operation of the booster or servo vacuum check valve. There is a check valve installed in the vacuum line from the engine to the brake booster.
To test the vacuum check valve, remove it from the vacuum line, noting the orientation of the valve in the line. Blow into the valve in the direction indicated by the arrow on the valve while you seal valve's other end with your finger. The valve should lift from its seat and permit pressure to escape. The valve must seal if you blow into its opposite end. Be sure to install the valve with the arrow pointing toward the brake booster.
Another possibility is that you got a new, defective master cylinder. Before putting the new cylinder in, I guess you were getting a "long" pedal, going to the floor. However, prior to this condition, I am guessing that the brakes worked fine. So really the only thing that was changed is the master cylinder, and now you have dragging brakes. I think the master cylinder might be high on my suspect list. Good luck, WWR.

 

[biggychase]

Re: Brakes stuck on... please help (WackyWabbitRacer)

Thanks for the help WackyWabbitRacer, i will try your suggestions as soon as I can find some time this weekend and keep you updated. The master cylinder would be my best guess also. Prior to the MC replacement, the rear pads had been low (non-existant) for quite some time and I was braking on basically nothing for a week or so (had to start braking a few hundred feet earlie than usual). I replaced the rear pads and adjuster springs, and then I noticed the MC was going long although the braking other wise was excellent, probably due to my pedal going to the floor while my rears were shot. Could anything else have gone wrong in my system while I was stupidly driving around for a week with basically no shoes in the drums? I'll check the vaccum line and valve as you suggested, and if all is well there, I'll take up my warrantee on the MC.
Thanks again