Phil94850 Posted May 27, 2008 Report Share Posted May 27, 2008 I have a 90 740 turbo with ABS brakes. i picked it up a couple of days ago and the brake pedal goes about 3/4 way down before the car will stop. I can pump the pedal and the pedal will firm up like it should. I went around and bled all 4 wheels, no change, i purchased a new brake master cyl., no change, one thing i noticed though, when i push my brake pedal a couple of time with the engine running my idle will start going up and down a little. When i leave the brake pedal alone the idle will smooth out. Im thinking a bad brake booster, but before i go tearing that thing off i checked my check valve that goes into the booster and i can blow air thru it in both directions. I can blow thru easy in one direction ( direction air would flow from booster to engine ) and blow thru air kinda harder the other direction. Im not exactly sure how the check valve is suppose to work if anyone knows that would help me. anyone have any ideas what my problem is ??? Link to comment Share on other sites More sharing options...
Phil94850 Posted May 27, 2008 Author Report Share Posted May 27, 2008 after thinking about it.... if my brake booster was faulty wouldnt i have a hard pedal ?? my pedal is pwr. assist its easy to push down it just goes way down too far.. Link to comment Share on other sites More sharing options...
MrWinkey Posted May 27, 2008 Report Share Posted May 27, 2008 Without the car running pump up the brake pedal firm. Now release it. Now go back lightly and push on the pedal. If it still sinks down pretty far you have air in the system. Actually when you installed the new master cylinder did you bench bleed it? Also what do the front rotors look like are they way undersize? Honestly I believe by your post you had a faulty master and installed a new one not bench bled. Link to comment Share on other sites More sharing options...
Three Fat Tigers Posted May 28, 2008 Report Share Posted May 28, 2008 Good point about the undersized or worn rotors, FCPgroton sold some cross drilled rotors to my brother and he had a similar issue with the pedal going too far down. The rotors were too skinny, already below spec for the car. Issue was more pronounced when the pads were worn down a bit.You really shouldn't be able to blow air the wrong way through the booster check valve. Cheap to replace though:http://www.fcpgroton.com/product-exec/prod.../category_id/57Otherwise, odds are there is still air in the lines or the ABS pump. Link to comment Share on other sites More sharing options...
PaThKu Posted June 1, 2008 Report Share Posted June 1, 2008 Did you check your brake fluid? Link to comment Share on other sites More sharing options...
Phil94850 Posted June 2, 2008 Author Report Share Posted June 2, 2008 i picked up a 90 740 turbo and the brake pedal has always been low on the car. I installed a reman master cyl from a-zone, no change, installed a brand new master cyl. , no change, bled all four wheels with someone pumping pedal no change, gravity bled, no change. i bled the master cyl before i installed also.after being very frustraded i decided to bleed the lines on the ABS unit, after doing that my pedal got alot better, not where it should be but alot better. anyone have any ideas why im having so much trouble with the brakes ?? Link to comment Share on other sites More sharing options...
Three Fat Tigers Posted June 2, 2008 Report Share Posted June 2, 2008 Two threads, same author, same subject, now merged rotor thicknessbrake pad thicknessair in the lines or in the ABS pump (still)issues with one or more caliperspossible degradation in the flexible lines (ballooning)Otherwise (I don't recall for certain) there may be an adjustment where the push-rod from the brake booster enters the rear of the MC. You might try a professional bleeding machine. Might also try another ABS pump. Link to comment Share on other sites More sharing options...
Phil94850 Posted June 3, 2008 Author Report Share Posted June 3, 2008 rotor thickness dont look bad, i installed new front pads ( it needed them anyways ), my pedal now is alot better than b4 but if i have to stop suddenly i dont have that hard pedal like i should. The pedal is still slowly dropping down if you hold press. on it. I think i have air in the ABS unit, ill probably try getting it press. bled, i hate doing it all the shops around here want an arm and a leg to do it. Link to comment Share on other sites More sharing options...
Phil94850 Posted June 3, 2008 Author Report Share Posted June 3, 2008 Mr. winkey... the master cyl's i bench bled both of them b4 i installed and it didnt help any. the only real change ive had was when i cracked the lines on the ABS.. Link to comment Share on other sites More sharing options...
Phil94850 Posted June 3, 2008 Author Report Share Posted June 3, 2008 i went out today and bled the ABS some more and now my pedal with the engine not running hardens up and doesnt leak down. When i start the car though, my pedal goes down too far, then if i hold press. against it, it will slowly drop ??? any ideas ?? Link to comment Share on other sites More sharing options...
MrWinkey Posted June 4, 2008 Report Share Posted June 4, 2008 Air..Mic. the rotors Link to comment Share on other sites More sharing options...
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