Brake System Problems. Help Please!! | FerrariChat

Brake System Problems. Help Please!!

Discussion in '308/328' started by Big Daddy, Dec 14, 2009.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. Big Daddy

    Big Daddy Karting

    Jan 3, 2009
    212
    Albuquerque, NM, USA
    Full Name:
    RJ
    I recently did some work on the brakes of my '81 GTSi, and now I can't get brake pressure to come up and the Brake Failure light is illuminating. I can't figure out what I could have done wrong! I have checked all the obvious things several times, so I am hoping someone has had a similar problem and it is something not so obvious that I have not thought of.

    Before I started work, the brakes were working pretty well. The cable for the parking brake was broken, and there was a little leaking around the adjustment screw on the rear right caliper. I decided to change the pads. The old ones were not very worn, but I did not know how old they were so I replaced them. The rotors were all within spec and smooth, so I did not do anything to them. The pedal was firm and the car stopped straight.

    I rebuilt the right rear caliper, repaired the parking brake mechanism, and had to remove the pistons on both front calipers and clean them up because they would not retract for the new pads. They functioned smoothly after I removed the gunk. I also sent the Master Cylinder out for a rebuild. I reassembled everything (correctly I thought) added fluid, and bled all four calipers until no more air was seen. I also bled the master cylinder.

    The brake pedal still went all the way down, and the Brake Failure lamp came on when the pedal reached bottom. So I bled all lines again and the same thing happened. And Again. I went thorough the whole system looking for lost motion, adjusting the rear pads again. There were no leaks, pads are all tight, no bulging hoses, but the same problems with the brake pedal still.

    If I pump the brake pedal, it rises and is firm and the brake failure lamp goes off. I think that means the new master cylinder is working correctly. The pedal stays hard for as long as I depress it. If I release the brake pedal and wait a few seconds, it goes soft again, travels all the way down, and the Brake Failure lamp comes on again.

    I am thinking the problem is somewhere in the system I don't understand. Could an air bubble be trapped at the shuttle valve, or the proportioning valve to the rear brakes? I can't find any way to bleed at those points. Could either of these items be damaged to the point of causing my pedal problems? Since the Brake Failure lamp goes off when I pump the pedal, I think the shuttle valve must be moving freely, but maybe there is something there I don't understand.

    As for the proportioning valve, fluid is bleeding freely from the rear screws, so I don't think it could be clogged. I don't know what else could go wrong there.

    I have thought about taking it somewhere that can pressure bleed, but since I have put about a gallon of fluid through the system, I can't believe there could be enough air trapped anywhere to cause a problem like this. It seems more like a lost motion problem, but I can't find any.

    The only other thing I can think of is maybe I screwed something up when I installed the master cylinder. I know the push rod has an adjustment screw on the end of it, but I did not change the setting of this screw when installing/uninstalling. Could that screw adjustment be causing a problem? Is there a procedure to check it?

    Please help if you have any ideas because I don't know what else to try and I need to get the wheels back on my car soon!

    Thanks for all your help!
     
  2. BillyD

    BillyD Formula 3
    Silver Subscribed

    Feb 28, 2004
    1,828
    Pacific Northwest
    Full Name:
    Bill
    Sounds to me like u just still have air in the system. I find its best to bench bleed a master cylinder b4 installing then bleed all 4 corners starting with the furthest from the master cylinder by the old "open bleeder, press pedal to floor, close bleeder, repeat"
    good luck
    Bill
     
  3. mike996

    mike996 F1 Veteran

    Jun 14, 2008
    6,871
    Full Name:
    Mike 996
    You can buy a cheap pressure bleeder for less than 50 bucks; they work fine. Buy one and never have this sort of problem again and never fool with pumping the pedal/opening and closing the caliper bleeder or with bench bleeding a master cylinder. The whole process will take maybe 20 minutes to completely change the fluid/bleed the system.
     
  4. CliffBeer

    CliffBeer Formula 3

    Apr 3, 2005
    2,198
    Seattle, Washington
    Full Name:
    Cliff
    RJ, ditto on the suggestion to get a DIY pressure bleeder. The Motive bleeder works well and is inexpensive: http://www.amazon.com/Motive-Products-Custom-Power-Bleeder/dp/B0002KM5M4

    As silly as it sounds, I've found it's also helpful to have a vacuum bleeder - for whatever reason the pressure bleeder couldn't remove all the air in the system and using a vacuum bleeder helped.

    It might be worth replacing the rubber brake lines - they can swell over a number of years, partially close up and create all kinds of havoc with bleeding the system (and braking your car!). I believe Tire Rack has good quality Goodrich stainless steel brake lines for your car for about $125.

    Good luck and persist!
     
  5. FasterIsBetter

    FasterIsBetter F1 Veteran

    Jul 22, 2004
    5,855
    NoNJ/Jupiter FL
    Full Name:
    Steve W.
    If I recall properly, those calipers only have one bleed valve per caliper. I know someone who had that problem you are having, and it turned out that the calipers had two bleed valves per caliper, and he simply forgot to also bleed the inside screws on all 4 wheels. As soon as they were bled properly, no more pedal problem.

    The other thing I've seen is someone installing the calipers on the wrong side of the car, that is, upside down. The bleed screw needs to be on the top, not the bottom. He couldn't get the brakes to bleed. When we looked at them it was obvious why. Once they were swapped and installed right side up, they worked fine.

    Don't know that either of these are relevant to you, but thought they were worth mentioning.
     
  6. Big Daddy

    Big Daddy Karting

    Jan 3, 2009
    212
    Albuquerque, NM, USA
    Full Name:
    RJ
    Thanks for your suggestions. The pedal does feel like there is still air somewhere in the system. But as I mentioned I have done everything possible to bleed it, so what I wanted to know is if there was something not so obvious that I was missing.

    From your posts there does not seem to be anything else I can do but tear the whole system down and start over. I'd hate to find out that it was something simple I just didn't know about.
     
  7. FasterIsBetter

    FasterIsBetter F1 Veteran

    Jul 22, 2004
    5,855
    NoNJ/Jupiter FL
    Full Name:
    Steve W.
    Sitting here scratching my head, trying to think what it could be. You said that you "cleaned up" the front calipers. Did you change the seals on the pistons, or just clean them? I don't know that it could cause your symptoms, but if the calipers were "gunked" up enough to keep the pistons from retracting, the rubber O-ring seals are probably shot and should be replaced. They should be stock ATE calipers, and the o-rings are not very expensive to replace (check the cross-reference threads, and you'll find the Porsche part number for those seals, and you can order them on-line from one of the Porsche parts folks for way less than the F-car replacements). I did it on mine, piece of cake.

    Beyond that, unless you didn't bench bleed the master and there is some air trapped in there, the rest of the system should purge itself if you've bled it properly. Assuming no leaks, can't imagine what it could be. Did you trace all the lines to be sure you are not leaking somewhere that you are just not seeing?
     
  8. Big Daddy

    Big Daddy Karting

    Jan 3, 2009
    212
    Albuquerque, NM, USA
    Full Name:
    RJ
    I did replace front seals and cleaned varnished gunk off the pistons and calipers. I can't find any leaks anywhere. The MC was checked again and there is no air present.

    Like I said, I was hoping there was something about the system that I didn't know.
     
  9. MarkCollins

    MarkCollins F1 Rookie
    Owner

    Jul 2, 2002
    3,202
    South England
    Full Name:
    Mark Collins
    I think the brake warning light is activated when the master cylinder level drops to low, so if the pedal is going to the floor and the light is coming on it would suggest by pumping the level in the master cylinder is falling quickly.

    I had a similar problem with my 355 where I couldn't get good pedal pressure but hadn't realised you could bleed the master cylinder (at two points) once done it was perfect.
     
  10. Big Daddy

    Big Daddy Karting

    Jan 3, 2009
    212
    Albuquerque, NM, USA
    Full Name:
    RJ
    For some reason, I had to bleed the front and rear brakes at the same time. When I did, I got a full pedal stroke and a lot of bubbles blew out the rear lines and some out the front. After doing this, the pedal was rock hard and the car brakes better than ever.

    I have no idea why it was necessary to do it this way, but it worked.
     
  11. FasterIsBetter

    FasterIsBetter F1 Veteran

    Jul 22, 2004
    5,855
    NoNJ/Jupiter FL
    Full Name:
    Steve W.
    That's a weird one, for sure. Never heard of that. Obviously, there was air in there. Usually, the "start with the farthest and work in" method clears all the air, i.e., right rear, left rear, right front, left front. Glad that doing it this unconventional way worked for you. I take it the entire system was drained from doing the work you did on the car. Perhaps that had something to do with it.

    Anyway, good that you have brakes again!
     

Share This Page