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Dust Boot

At some point if you track your MINI, you’ll notice that you’ve destroyed a rear dust boot. It will tear because you caught the rubber in the pad retaining clip thanks to its poor design, or you’ll cook the rubber and notice it has cracked to pieces and decide it needs to be replaced.  If you talk to your dealer, you’ll probably hear that the caliper cannot be serviced and that you have to buy a new one, but if you look in the BMW parts catalog (see picture below, no. 12) you’ll find part number 34216757250 which is surprisingly called “repair set brake caliper” and only costs about $25.

At this point, you’ll be thinking to yourself, “those bastards, they’re ripping me off by saying it cannot be serviced.” And in your righteous indignation, you order the part and determine to do it yourself. The fact is your dealer is right. And there is this kit available. The kit only includes the dust boot. To “service” the caliper, you also need to replace the piston seal which is not available. Before you decide to skip the seal, you have to ask why the boot needs to be replaced. If you really cooked the caliper. By cooked, we’re talking sustained caliper temperature above 550 degrees F, then you need to replace the seal and that means purchasing a new or remanufactured caliper. If the boot is torn because it’s becoming brittle with age or you pinched it with the brake pad retaining clip, then you’re probably safe just replacing the dust boot.  But don’t rejoice too quickly, however.  Be prepared for hours of frustration if you don’t have the proper tool.

The dust boot simply presses on the caliper, but like so many things, the devil is in the details. To press it on, you need to hold the caliper securely with one hand, use a screw driver to hold the bottom of the boot in place, use a third hand to press on the upper left, and a fourth hand to press the upper right. That’s hard enough to do with the car on a lift, and impossible to do with the car on jack stands. So if you don’t want to remove the caliper and work on a bench, and don’t want to pay an outrageous amount for a tool you’ll use once every couple of years, then here’s how you roll your own tool. (Follow at own risk; no wagering.)

Ideally you want something shaped like a small measuring cup, 1.8 inches inner diameter/2.0 inches out diameter, and about an inch deep. If you can’t find one, the plastic cap from a spray can may work.  I used a cap from a can of testers paint. Clip the cap in a couple of places (which I’ll explain later) and wrap very tightly with electrical tape. You’re going to first position the boot on the caliper, press your make-shift tool over it, then use your brake caliper tool to press it on.  The cuts in the side were to make the diameter smaller when you wrapped it in tape, but also so that when you release the tape, you can pull the cap off without removing the dust boot.  When complete, be sure to press the inner part of the boot into the furthest groove in the piston so the dust boot and brake pad retaining clip are not in the same groove. Good luck.

If anyone has found an actual tool for this that doesn’t cost a fortune, please post a link in the comments.

parts diagram Clean piston press here