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TOPIC: brakes

brakes 6 years, 11 months ago #15776

  • rd7839
  • Endurance Racer
  • Posts: 625
Need some help! Since I went thru the car this offseason I've had no brakes. First it was a soft pedal. After several bleeds, both at home and professionally I still had nothing. Swapped out calipers, master cylinder(4 times, 3 different MS's),front rotors, put in street pads, front brake lines, checked all the hard lines for kinks. We were able to get a hard pedal but it took both legs to slow the car. Now I'm replacing everything, new rotors, rebuilt calipers different master cylinder, 4 new stainless brake lines, and a brake booster off a known good car.

Am I missing something? Has anybody else had this problem? Believe me when I say we bled them thoroughly. I lost count of how many cans of fluid we went through. We bench bled the masters before they went in(not every time but at least twice)

I'm starting to replace the booster and found this line disconnected. What does it go to and is it important? Could it be the check valve on the booster that's bad? Is there a bias valve somewhere that I don't know about?

Any help would be deeply appreciated. I'm so frustrated I'm ready to sell the car as junk!
Last Edit: 6 years, 11 months ago by rd7839.

Re: brakes 6 years, 11 months ago #15777

  • rd7839
  • Endurance Racer
  • Posts: 625
Oh, and we did like for like, Girling with Girling and Ate with Ate.

Re: brakes 6 years, 11 months ago #15783

  • cbuzzetti
  • Endurance Racer
  • 944 Spec = The best racing on the planet
  • Posts: 1192
Ron it sounds like a brake booster problem to me but I am no expert. Things like this can drive you crazy.

Be sure to let us know what you find.
2018 NASA 944Spec National Champ
2018 NASA ST5 P2 944 Nationals COTA
2017 NASA 944Spec WSC P3
2016 NASA PTD-944 WSC P2
2015 NASA GTS1 Western Champion
2014 NASA 944Spec Western Champion
2013 NASA 944Spec So-Cal Regional Champion
2013 NASA 944Spec National P3
2010 NASA GTS-1 National Champion
2010 NASA 944Spec National P3
2010 NASA So-Cal 944Spec Regional Champion
2009 NASA 944Spec National Champion

Re: brakes 6 years, 11 months ago #15786

  • AgRacer
  • Administrator
  • Posts: 712
Do you still have the vacuum diagram intact under the hood? That should reference where that line goes to if you do. I referred to it many times when I redid my vacuum lines.

I wouldnt immediately say the booster is bad, just that its not boosting properly which could be due to a loss of vacuum being supplied to it somehow. Can you block off all other vacuum lines so it is getting an uninterupted vacuum supply off the nipple on the bottom of the intake manifold?

My car is an 83 with an 88 motor, but still had the stock vacuum setup. I recently deleted everything but the essentials which basically cut it down to:

1) 1 vacuum line off the Throttle Body that Ys into the two connections on the Fuel rail

2) 1 larger line off the bottom of the intake manifold that connects directly into the booster.

I am not aware of any additional vacuum lines needed to operate the car. Others may be needed if you still have AC/Heat/etc but those are all creature comforts that most of us got rid of long ago.

Lastly, I plumed the vent off the top of the AOS to a catch can that is vented to the atmosphere. Prior to doing this, I was having a large amount of oily nastiness flow back into the intake and gum up the works.

Hope this helps. If you need a picture of the vacuum diagram, I think somebody here can dig one up.
J. Stanley
NASA-SE Region 944 Spec Series Director
Yellow #60

Re: brakes 6 years, 11 months ago #15787

  • joeblow
  • Seasoned Racer
  • Old Racer
  • Posts: 226
Yes the check valves can go bad and will cause the issue you describe. Also incorrect vacume plumbing can do it too.

As a side note, even if you fix the issue, the street pads will not feel right either as they have much less bite.
Old Racer!

Re: brakes 6 years, 11 months ago #15792

  • rd7839
  • Endurance Racer
  • Posts: 625
Among the parts I have already bought I ordered a check valve today. So that will make everything but the hardlines replaced with new or used from known working cars.

BTW Joe, I just got back from your neck of the woods. Had to make a quick dash to Salt Lake City and as I drove out Bangerter towards the airport I thought of you, of course I don't know you but as every plane landed, I wondered if you were flying one.
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