fading brakes

[Elk]

At work we have a 1990 250 with 150,000 miles on it. The problem is the brakes. We have replaced the booster, master cylinder, brakes themselves, wheel cylinders, calipers. After all this we still get brake fade. Infact today you could push the pedel clear to the floor and barely stop and the brake light would come on and as soon as I released the pedel the light goes out. We have had some problems with the adjusters, have put the springs on exactly as the book says.

 

[AlK]

I am not a brake expert, but I would suspect the master brake cylinder. I had a similar problem with our car. The brakes held fine if I really hammerd them and pushed down hard, but when I applied a steady (not to hard pressure) the pedal would fade to the bottom. My 2 cents.

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Al

 

[fastmark]

The way I test for a bad MS is pump the brakes and apply hard pressure. Then I let up a little. If I can let up and it starts losing pedal, then I know it is bypassing. It would not be the first time someone got a bad MS out of the box.

 

[DJP]

I recently had the same problem in my '89. When applying the brakes, the pedal would sink to the floor, and the Brake / Antilock light would come on. The problem was a leaky rear wheel cylinder which I discovered after noticing the rear reservoir in the master cylinder was extremely low. When I replaced my rear brakes last year, I only replaced one wheel cylinder, since the one on the other side looked good. A year later, the other side was leaking and causing a "brake fade" condition. I highly recommend replacing both wheel cylinders when doing a rear brake job, no matter how good they look! Especially when you can get new ones for only $12. 00 each!

 

[hdm48]

I've said it before and I'll say it again. The rear wheel ABS valve can cause this problem. An easy way to check this is to listen under the rear of the truck while the brakes are applied[engine off]. If the valve is bad you will hear a hissing sound coming from the valve. Push on the brakes hard. I'm not saying this IS your problem, just a possibility. I went through this myself and fixed it myself. good luck

 

[jsimpson]

I put three master cylinders on my Buick (rebuilt) before finally putting a new one on and solving the problem.