fadeing brake pedal

[cedarjames]

hello there
I am working on a 1998 windy I have replaced the master cyl and still have a fading brake pedal. I have unpluged the abs and still have the same prob. It still feels like a bad mstr cyl. I have adjusted the rears up and bled completly. any help

[12Ounce]

Keep in mind that each wheel has to do its own "retracting"... and pulling fluid from the master cylinder in the process. The allows/helps the master cylinder to fully return.

Make sure the calipers are free to move in-out .. by greasing the splines, or pins, or whatever they slide on. (Different designs for different years) (The rubber o-ring around the caliper acts as a seal and a RETURN SPRING.)

If you have drums on the rear make sure the shoes are edge-lubricated so they will slide on the backing plate. Be sure the pistons are not stuck in the slave cylinders and there is silicone lubricant inside the dust boots. May be a good time to replace the wheel cylinders and the return springs and other hardware ... depends on rust/wear conditions.

[cedarjames]

Originally Posted by 12Ounce

Keep in mind that each wheel has to do its own "retracting"... and pulling fluid from the master cylinder in the process. The allows/helps the master cylinder to fully return.

Make sure the calipers are free to move in-out .. by greasing the splines, or pins, or whatever they slide on. (Different designs for different years) (The rubber o-ring around the caliper acts as a seal and a RETURN SPRING.)

If you have drums on the rear make sure the shoes are edge-lubricated so they will slide on the backing plate. Be sure the pistons are not stuck in the slave cylinders and there is silicone lubricant inside the dust boots. May be a good time to replace the wheel cylinders and the return springs and other hardware ... depends on rust/wear conditions.

I forgot to mention all that was done. I have pulled the calipers and cked movement(slides) and had rear drums off and inspected hard ware and wheelcylinders i didnot pull the boots and ck for silicone but had no seepage and springs dont look that old. I understand your explaination. ieoss stiking brake part not leting the master to return . this pedal is at the top when you first apply and then slowly fades to the floor. could this be abs conected or did i just get a bad master cyl?

thank you very much for your help.

[12Ounce]

I believe you are right in being suspicious about the master cylinder since the pedal/& master cylinder apparently is/are fully returning. I have purchased a bad aftermarket master cylinder before. I don't see how ABS could be the blame.

... but make sure a bit of entrained air is not the culprit. I always employ a second person and do the old "pump and bleed" process.

[cedarjames]

12 ounce thank you. I am going to order a new master cuyl tomorow. I hope thats it. for my customers sake.

[weaselgeezer]

I am having the same problem on my 98ws 3.8 with traction control.
The pedal sinks to the floor & brakeing is only 5% of what it should be.
At first I condemed the master cylinder but after inspection & cleaning & finding no internal damage I bench bled, refilled & put it back on, only I pluggrd both outlet ports with metal plugs. The pedal was ROCK SOLID. I reconnected both lines & got my sinking pedal back. I figure that eliminates the master cylinder & booster as the culprets. I am now looking at the hydraulic control unit (the one with all the tubes) not the ABS module as the possible location of internal fluid by pass.

Has any one else been down this road?

Regards Weaselgeezer

[12Ounce]

I would say the master cylinder is not off the "hook". Your bench test was good, but does not prove the master capable of refilling itself while connected to the system.

[LeSabre97mint]

Originally Posted by 12Ounce

I would say the master cylinder is not off the "hook". Your bench test was good, but does not prove the master capable of refilling itself while connected to the system.

Hello guys

I seem to remember reading some where that the ABS unit would need to be bled if air was allowed to get into it. I think this is done by a computer interfacing the ABS unit. Anyone else have any input?

Regards

Dan

[weaselgeezer]

Just did Chiltons test for hydraulic control unit & it flunked. One of the two accumulators is not working & is probably allowinfg fluid to bypass internally.