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

[Dave M]

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 :D

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

[Kalevera]

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.

[Dave M]

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

[Chris'91'525i]

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.

[winfred]

drums suck buy something with discs :D 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 :D

[Bill R.]

The following attachment

[winfred]

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


The following attachment

[92E34]

I'd say its something with the brake lines.

I just had the ones on my 87 subdivision collapse.

[Dave M]

The following attachment

Wow,

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

Dave M

[DaveVoorhis]

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.

[Dave M]

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.

We have a winner :D. As much as they looked fine, even when carefully compared to the other side, they were in fact, F'ukedd wit fluid.

Thanks for the kick in the pants.

Bill, I did inquire about the recall notice you provided, but the nice gentlemen at GM weren't too interested in a 14 year old rust bucket. I figured by the time they got back to me, then tried to charge me for something, I'd be better off trying the fix on my own. Anyhow, thanks again. Glady I didn't have to go down that road :)

back on the road, again......

Dave M