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  • 02-07-2011, 09:59 AM
    fritracer

    Forgot 1 other cause...

    you could have a brake hose breaking down and expanding more than normal under pressure. You can normally see this by having sombody press on the brakes while you watch the hoses. Fritracer
    Cincinnati, OH
    2000 540ia Sport Package 9/99 Silver/Black
    1970 Dodge Challenger T/A 420 stroker w/6 Pak 430 HP,
    510 lbft torque
  • 02-07-2011, 09:57 AM
    fritracer

    Here we go again...

    The only things that will cause the problem you are describing is: the pads being pushed away from the rotor surface due to warped rotors, out of square caliper mounting, caliper cup seal installed wrong (this usually leaks though) or M/C piston cups not sealing. E39 brakes are not mushy or fair; both of the ones I have owned stopped better and had the best pedal feel of any car I have owned.
    I had a similar issue with my wifes Suburban; worked on it for a while until I found the problem; it always ahd a crappy pedal and lousy stopping. I talked to a lot of people who owned this model and they all said that is how it is; my reply was [Oops!], no body would put something this crappy on the road. What I found was the ABS module was holding air in it even with the lines and bleeder cracked loose to bleed it. Lousy design. I had to remove the mounting bolts and move the thing around as I was power bleeding the brakes. Now this thing has a great pedal and stops very well. You might have air caught in the system that will not come out. I have not had that type of issue with a BMW. My bet is on the M/C but check all the other causes first. Is there a rebuild kit available for these cars? If so, that will knock a bunch of the cost out and add some labor, but if you are doing it yourself, what is a 1/2 hr longer?Fritracer
    Cincinnati, OH
    2000 540ia Sport Package 9/99 Silver/Black
    1970 Dodge Challenger T/A 420 stroker w/6 Pak 430 HP,
    510 lbft torque
  • 02-05-2011, 12:40 PM
    Craig in Canada

    Re: So - should I replace my master cylinder?

    I hear ya.... I just which I could be more sure than spend $300 and a huge PITA job to see if it's fixed or not, that's all.

    On the other hand, it may have been "not quite right" the entire time I've had the car. Remember how I was mentioning that I never thought the E39 brakes were all that amazing and didn't modulate well. During my fall testing with fresh rear pads (that didn't have crumbling backing plates) they were pretty great on the "double press".

    If I'm going to think positive, that's the story I'll tell myself LOL. They were never right and this will make them awesome. Maybe the first owner didn't put a brick under the pedal or something and damaged a seal when the car was nearly new.

  • 02-04-2011, 02:33 PM
    Eurodavid

    Re: So - should I replace my master cylinder?

    Craig,

    Maybe it is not your car, but your knee or foot is getting soft---HAHA!), j/k ya.

    If you've rebuilt those calipers, and are dang sure the pistons are working properly (sliding smooth as silk), then given what you went through last year, what else could it be besides the MC??

    I think you're running out of targets.

    Eurodavid
  • 02-04-2011, 10:39 AM
    Craig in Canada

    So - should I replace my master cylinder?

    I won't drag up my old brake thread from the fall, but it's
    here.

    I still have this behaviour continuing through the winter to a certain extent. The pedal is firm, but lower on first application. On second application it's better but after time has passed it is "less better" than right after a bleed in warmer weather. I've activated ASC/ABS a bunch of times since the slippery weather is here now and I can do it without being hard on the equipment.

    The master cylinder job looks like a PITA, at least the inside portion, and MCs aren't cheap. I can save over $100 I'd say by ordering an MC from autohausAZ to my parents in FL while they are down there.

    How sure are "we" that I need a new MC and it's not something else? If I need it no matter what I might as well save $100. If there's more troubleshooting and power bleeding to be done before being sure then there's no reason for me to waste over $200.

    Thanks, roadfly!

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