Master cylinder going?

Since I replaced my rotors and brake pads before last ZuZoo I have been a little worried about my brakes. They seemed to work just fine on the street, but in Moab I noticed that my pedal would hit the floor after standing on it for a while to creep down some obsticles.

I've bled and re-bled the brakes and there doesn't seem to be any air left in the system so I think I'm good there. The pedal is firm and I can panic stop with the best of them, but if I'm sitting at a stop light and I really press down on the pedal it slowly drops all the way to the floor. Since it stops fine under normal conditions, and only drops the pedal when I stand on it for a few seconds, I'm wondering if my master cylinder is dying. The fact that the pedal drops tells me that maybe the seals might be leaking and fluid is pushing past them back into the reservoir under constant pedal pressure.

Opinions?

If you can't find brake fluid squrting out somewhere, then I think you self-diagnosis may be right.

My question is, what kind of pads/rotors do you have now? I had absolutely HORRID (and scary at time too) brake performance with after market pads. Once I replaced the after market pads with stock pads, my braking is back to good and strong.

Bart

VehiGAS, I did find a small leak in one of the stainless steel lines that I installed (my fault because I didn't tighten it down well enough), but the pedal drop was the same before and after fixing it.

Bart, I'm running drilled and slotted rotors by SP Performance with stock brake pads and the VX will stop on a dime and give me change if I need it to. Once I'm stopped, though, if I keep pushing on the pedal it will eventually go down to the floor. That's why I'm thinking that the seals in the master cylinder are going bad because they work initially, but the fluid must creep by them under additional pressure.

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Originally Posted by MSHardeman

Bart, I'm running drilled and slotted rotors by SP Performance with stock brake pads and the VX will stop on a dime and give me change if I need it to. Once I'm stopped, though, if I keep pushing on the pedal it will eventually go down to the floor. That's why I'm thinking that the seals in the master cylinder are going bad because they work initially, but the fluid must creep by them under additional pressure.

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Hmmm, I see. That sounds bad. I wonder how much a new master cylinder costs?

Bart

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Originally Posted by MSHardeman

Once I'm stopped, though, if I keep pushing on the pedal it will eventually go down to the floor. That's why I'm thinking that the seals in the master cylinder are going bad because they work initially, but the fluid must creep by them under additional pressure.

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Based on my own 30 years of wrenching on wretched vehicles, I think you're dead on w/your diagnosis...

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Originally Posted by nfpgasmask

My question is, what kind of pads/rotors do you have now? I had absolutely HORRID (and scary at time too) brake performance with after market pads. Once I replaced the after market pads with stock pads, my braking is back to good and strong.

Bart

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I have had no problems with aftermarket pads.I only use good ceramic pads. Which I believe the stock pads are. shawn