Abnormal Brake Pedal

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J

Jeff Harwanko

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Jun 24, 2005
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Wilmington, DE
Back story:

Replaced rear shoes, front pads and rotors, installed speed bleeders, and then power bled the system.



Problem:

Pedal is firm and high with engine off. However, during driving conditions sometimes the pedal is high (where it should be after bleeding) and sometimes the pedal requires much more travel to stop the vehicle.



Ideas:

-Could the power booster have an internal vacuum leak causing the erradic behavior?



Any ideas anyone?



Thanks!
 
It's usually either the master cylinder or the brake booster, it has been the master cylinder in my past experiences.
 
My '03 Trac has the same issue after replacing the front & rear brakes 12 months ago. Sometimes it acts normal and other times it takes more effort to stop the vehicle. I'll check out the items mentioned above. Thanks.
 
did you remove the bleeders. to push the pistons back. if not, you may have push old contaminated fluid into the abs system.
 
Thanks for the input guys. I'll check the "check valve" on the booster this weekend. As far as back flushing old fluid into the abs, I did remove the bleeders before pushing the pistons back. When finished I power bled the entire system until new fluid came out of each bleeder.



Keep the ideas coming!
 
As far as the booster goes. I had one on my t-bird rupture the diaprham. Braking at low rpm caused the motor to stumble, engine vacuum lose. The symtoms were the same, as yours when braking. IIRC,it was doing that before the engine stumble started. I found in the t-bird haynes repair manual, how to test it. At this time I cant remember the procedure.
 
After some further research...To test if the brake booster is performing- With the engine off depress the brake pedal several times to remove residual vacuum in the booster. Pedal should be high and firm. With your foot on the brake pedal, start the engine. The brake pedal should then depress further with the same pressure.



Well, I performed this test and the pedal did depress further when the engine started.... a lot further in fact. So much that I feel it may be excess air in the system or a bad master cylinder.



I plan to pressure bleed the system again, but with the engine running. (Somewhere I read that if the engine is running, you have a greater chance of getting air out of the ABS system).

If this doesn't solve the problem, I guess I'll replace the master cylinder.
 
Well it's definately not the booster. Next step is to wait for a buddy to return my jackstands:angry: then I will rebleed the whole system (master cylinder too this time) old school style...pump the brakes..open the bleeder etc etc. I will try bleeding it with the engine running this time to see I get more positive feedback thru the pedal. Thanks for all the input everybody. I will keep you informed after I get a chance to rebleed the brakes.
 
Alright....so I finally got my jackstands back. I'm going to rebleed the entire system, including the master cylinder. One question though....do I bleed the master cylinder first, or do I bleed it last?
 

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