brake pedal issues

[win911]

Hi Everyone,

Working on my friends 2001 C4 with 40k miles on it. His brake pedal is soft and going staight to the floor with minimal stopping. The car is tracked 2-3 times a year. The brake pads and rotors are fine. Fluid is ATE blue. We re-bled the system and pedal is back to normal feel, but after 10 minutes of use the brake pedal is back down to the floor. NO fluid loss anywhere. any thoughts?

I have searched this forum and all I see is the master cylinder.

If it is the master cylinder.... Do I need to bleed the ABS?

Thanks

[RFM]

The master cylinder could be the culprit (brake fluid is leaking inside the brake booster), but i have seen some leaking ABS units as well. Check under the front trunk carpet, in the ABS unit area, for brake fluid traces. The master cylinder can be bleed separately, start bleeding the new cylinder, right rear wheel, left rear wheel, right front wheel and left front wheel with at least one litre of new brake fluid.

[win911]

Thanks..

No leaks under carpet...no leaks on the floor... not loosing any fluid in the master cylinder.

Besides the master cylinder....any other parts I should look at. I am almost sure it's the master cylinder, but just want to make sure.

Just to verify... I do not need to bleed the ABS if I change the master cylinder?

Thanks

[RFM]

As i mentioned in the post above, no need to bleed the ABS unit if you bleed the new master cylinder first. The brake calipers must be bleed on the inner nipple first and than the outer nipple.

[Mother]

Same problem I have and bleed the brakes till I was blue in the face, also installed new master with no change, I just replaced the clutch slave cyl which was leaking, but did not fix brakes. I ended up slamming on by brakes in forward and reverse and they DID lockup which I did not think they should with ABS, but the pedal did come back up like I had a sticking caliper. Time will tell if they sink again. Maybe just sticking worth a try.

[win911]

Mother... so no change by replacing the master cylinder? How hard was it to change the master cylinder?

[wvicary]

The master cylinder can by-pass internally and cause a low pedal. Be sure to fully bleed the replacement unit before installation.

[Mother]

Mother... so no change by replacing the master cylinder? How hard was it to change the master cylinder?

Nope no change. I was going to change it, but let my indy do it, he told me that they are very rare to go out but I was running out of options. Did you try the slamming on the brakes forward and reverse doing about 10-15 mph? My wheels locked up which leads me to beleive that the ABS is shot or going. Edited July 15, 2009 by Mother

[win911]

Haven't tried the slamming of the pedal yet. Going to replaced the M/C and see what happens....much cheaper than the ABS...

Thanks guys

[Mother]

GL, I agree the ABS is pricey. I'm not sure but I think Durametric can scan for any problems/error codes with ABS. Keep us posted.

Edited July 15, 2009 by Mother

[win911]

UPDATE:

The problem was the ABS system. Just a little under $1000.00 to replace. She is back on the road.

So the symptom was soft brake pedal... initially felt like air in system... bled system.. worked for the first 10 mins. them back to being soft....

Change ABS and all is well.

Thanks