K Bike Tech

Remove Rear Brake Rotor

The two bolts that hold the rear brake rotor onto the final drive are notoriously difficult to remove because BMW used some sort of mega thread locker on them and the 5mm Allen head bolts are somewhat soft metal. And potential corrosion in the threads over time doesn't help. Therefore if you just try to back them out normally then the Allen heads of the bolts will often strip.

Before you attempt to remove them heat them up a lot with a torch to degrade the thread locker. Then use a high quality 5mm Allen wrench (like the Heyco one that comes in the factory toolkit) with a cheater bar - like the factory extension tool:

It's best to try to remove these bolts with the final drive still installed on the bike. Otherwise, with the final drive removed, the rotor will turn when you attempt to loosen the bolts.

Even using heat and a good Allen wrench it's still quite possible to strip the one or both of the bolt heads. However, this isn't a big deal. You just need to drill the countersunk heads off of the bolts. Be careful not to drill too deep though because you want as much of the leftover threads as possible remaining.

Once the bolt heads are drilled off the rotor can be removed. Then use Vise-Grips to get the rest of the bolts out.

If you're attempting to remove the rotor bolts with the final drive off of the bike then you can install two of the lug bolts and use a piece of pipe for leverage to keep the rotor from turning.

Replacement Bolts: The factory replacement bolts (Part 34212330021) are M8x20 with pre-applied thread locker and, from the BMW shop manual, should be torqued to 21 Nm.

However, I just use M8x20 countersunk (a.k.a. flat) bolts from the local hardware store. I put anti-seize on the threads and only torque them by "pretty tight" by hand. I use anti-seize and not too much torque in case I ever need to remove the rotor in the future.

In my opinion, you don't need thread locker or a ton of toque on the rear rotor bolts because with the rear wheel installed the four lug bolts will hold the rotor in place.