Sticky Caliper?

[Chris in Laguna Beach]

On my way home this evening in my 91 535i noise started coming from my left rear wheel when I hit the brake pedal. I could hear an impact sound when the brakes engaged, then a scraping sound until I released the brake pedal. If I brake hard, the left rear wheel brake will engage normally at first, then engage violently and stop hard. It releases when I release the pedal. Seemed to be getting worse in the few miles as I drove home.

I replaced all pads and rotors in December 2006 and have driven about 5000 miles since with no problems. At that time I replaced all brake lines with new SS lines, except the left rear hose (above the trailing arm) going to the problem caliper, which had a stripped fastener.

Could this be a:

1. Stuck caliper?
2. Clogged brake line--the one I didn't replace?
3. Something else (e.g. ABS malfunction)?

[Mr._Graybeard]

If a sticky caliper were the issue, it wouldn't stop acting up when you let off the pedal, IMO. Same thing with the brake hose. But it's hard to figure out what's going on from your description. An impact sound would suggest something is moving around (flexing) excessively. Caliper bushings?

If you want to replace that old hose with the stripped fastener, BTW, get yourself a Vise Grips LW4 Locking Wrench. It's the best tool I've ever found for dealing with troublesome hard line fittings. It will not slip, even if the flats have been rounded off.

[Dave M]

Agree with Grayybeard. If it is a caliper issue, it might not release as nicely as you describe. Not too sure about the brakeline, but my instinct says not an issue. In order to rule out the ABS, disable it. I've never done it on the e34, but have on a couple of others vehicles for this purpose. Should be as simple as removing connectors at the unit under the hood, or removing the sensors from the hubs. Do both sides of course.

Check for brake fluid leaking in the area. If it has managed to impregnate the pad, it will grab hard and cause the symptoms you describe. Swap the pads around and see if the problem follows. You should be able to troubleshoot this one.

Good luck, let us know what happens.

Dave M

[Chris in Laguna Beach]

Ok, I got under the car this morning, and the problem was simple: the mounting bolt had fallen out, and the remaining bolt was very loose. Replaced the bolt and tightened the other, and it's as good as new. I guess the bolt had worked its way loose since the brake job in December. I tightened up the other caliper mounting bolts as well for extra security.

Thanks to Dave and Graybeard for your advice.