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Thread: Drum brake lock-up on the winter beater. Need advice.

  1. #1
    Join Date
    Jan 2004
    Location
    Thunder Bay, Ontario
    Posts
    2,538

    Default Drum brake lock-up on the winter beater. Need advice.

    Stats: 1993 Pontiac Funbird
    Rear drums, four wheel anti-lock
    Pedal feels firm
    Shoes are at most 1/2 worn.
    When inspecting brake internals, everything appears fine.

    The blue bomber has developed an interesting braking issue (at least its interesting to me). The rear pass. drum locks up under moderate brake pedal pressure. I found a leaky wheel cylinder and assumed I had it solved.

    Not so simple. So far I have:

    1) Replaced the wheel cylinder. No change
    2) Swapped drums from left to right. No change
    3) Tightened both adjusters so the drums fit more snuggly over the pads. No dice.
    4) For $hits, I disabled the anti-lock. You guessed it, locks up even better

    So far, I've assumed the shoes are OK, but this evening I noticed that they're slightly more worn in the middle portions (both pass. and driver sides). I will replacing shoes tomorrow and I'll give both rear lines a good blead. But, pending no improvement, what else might it be.

    Very curious, any ideas appreciated.

    Dave M

    10/90 Build 525im, 630,000+km, Eibach/Sachs, Engine Rebuild
    *RIP Oskar the DOG *

  2. #2
    Join Date
    Oct 2004
    Posts
    3,395

    Default

    Dave,

    Given that I know nothing about GM stuff I can only venture a guess.

    I bet if you walk back from the wheel cylinder you'll find a junction and a proportioning valve that is sticking. Leaking cylinder may have exacerbated the situation.

    From what I've been told, the majority of early GM ABS are what people I've wrenched with call, "That awful Bendix system." If I am not mistaken, it is a three circuit system, just like on E30 and other early BMW ABS cars, so there's no need to send discrete lines to the rear for each corner.

  3. #3
    Join Date
    Jan 2004
    Location
    Thunder Bay, Ontario
    Posts
    2,538

    Default

    Thanks for the quick reply Whit.

    Would the fact that I have four lines exiting the master cylinder eliminate the "proportioning valve"? I'm almost certain there are discrete lines to each corner.........damn it

    Hmmmm,

    Dave M

    10/90 Build 525im, 630,000+km, Eibach/Sachs, Engine Rebuild
    *RIP Oskar the DOG *

  4. #4
    Join Date
    Jul 2005
    Location
    North SF bay area Delta region
    Posts
    211

    Default

    One thing I use to see a lot when I wrenched fulltime, is the brake shoes mixed up.
    Both primary shoes on one side and the secondary shoes on the other.
    Or one side you would see the the primary shoe on the front, and the secondary on the back, while the other side has correctly installed shoes.

    The primary shoe, (the one with more brake lining surface area) goes to the rear. And the secondary shoe(one with less lining material) going to the front is the correct installation.

    I'd check or replace the other wheel Cyl. too. make sure the pistons in it move freely in and out of Cylinder.
    1991 525i M50 5 Sp.
    N.California

    America is all about speed. Hot, nasty, badass speed. -Eleanor Roosevelt

  5. #5
    Join Date
    Dec 2003
    Location
    baton rouge, loserana
    Posts
    6,922

    Default

    drums suck buy something with discs i renewed my hatred of drums last saturday when i did the shoes on da truck, 13"x3.5" shoes bigger then the wheels of some cars
    all america wants is cold beer warm cat and a place to take a poop with a door on it

  6. #6
    Join Date
    Jan 2004
    Posts
    4,150

    Default This might be of some use.

    The following attachment
    Attached Images Attached Images  


  7. #7
    Join Date
    Dec 2003
    Location
    baton rouge, loserana
    Posts
    6,922

    Default

    nice, check valve brake hoses, my favorite is check valve abs pump

    Quote Originally Posted by Bill R.
    The following attachment
    all america wants is cold beer warm cat and a place to take a poop with a door on it

  8. #8
    Join Date
    Sep 2006
    Location
    Arizona
    Posts
    108

    Default

    I'd say its something with the brake lines.

    I just had the ones on my 87 subdivision collapse.

  9. #9
    Join Date
    Jan 2004
    Location
    Thunder Bay, Ontario
    Posts
    2,538

    Default

    Quote Originally Posted by Bill R.
    The following attachment
    Wow,

    Thanks Bill. I'll be bringing the notice you posted into a dealer. The forum strikes again

    Dave M

    10/90 Build 525im, 630,000+km, Eibach/Sachs, Engine Rebuild
    *RIP Oskar the DOG *

  10. #10
    Join Date
    Mar 2006
    Location
    Derbyshire, UK
    Posts
    872

    Default

    The brake shoe linings might be poisoned with leaked brake fluid, which will make them grabby. I used to fix brakes on 50's cars, and that wasn't unusual.

    1997 535i V8
    5spd, OBC, A/C, cruise, BMW phone, factory M-Tech wheel & suspension, 18" Alpinas

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