I’m going to powder coat the wheels, so I remove the disk brake rotors I refurbish the three rotors to remove grunge and get the patina on the disk carriers back to factory condition. I also clean out the holes and sand the disks so the new disk pads will bed in and not get fouled from brake pad grunge baked on the rotor or dirt and grunge lodged inside the disk brake rotor holes.
I also removed the wheel bearings before having the wheels powder coated. There is a separate document about how to replace the wheel bearings.
I replace the two rear wheel safety straps with tabs that are bent along the side of the bolts to keep them from backing out. I treat these as a “use once” part.
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Here is a short video summarizing this work.
VIDEO: 1983 R100RS Remove-Refurbish-Install Disk Brake Rotors
Remove Rear Rotor
The rear wheel has a single brake rotor on the left side of the wheel. It’s bolted to the wheel hub with five hex head bolts. These bolts are in blind holes so there are no nuts. The bolts are secured with metal strips with tabs that bend over the face of the bolts to prevent them from turning.
I use a screw drive and hammer to flatten the metal tabs on the strips. Then I remove the five bolts.
The brake rotor and it’s hub pull off the center hub of the wheel.
Rear Wheel Details
The left side of the rear wheel hub is dished and the right side has a flat hub where the disk brake rotor mounts.
On the left side of the wheel are a number of markings including an arrow showing wheel rotation. The numbers that look like 11 digit part numbers are not part numbers, they are casting numbers. The markings indicate the rim is 2.75 inches x 18 inches.
Remove Front Brake Rotors
There are two disk brake rotors on the front. They are not marked “Left” or “Right”, but they have mated to the disk pads. In general, it’s a good idea to keep them on the same side when you reinstall the rotors so the disk brake pads don’t have to bed in again on a different rotor.
I’m replacing the caliper pads, but I mark the rotors so I return them to the same side I removed them from. Why Not?
It’s easy to damage the rotors if you place them on the ground or work bench when you work on the wheel. I use some 2×4 blocks under the rim to keep the faces of the disk brake rotors off the floor. The rotors are thin and you can bend them if you aren’t careful.
There are five Allan bolts with locking nuts that secure both rotors. The bolts go through the wheels. The lock nuts are on the left side of the wheel and the Allan bolt heads are on the right side of the wheel.
I remove the five bolts. The disc brake rotors pull off the hubs the same way the rear brake rotor did.
Front Wheel Details
One important item to verify with these cast, aka “snowflake”, wheels is that it’s one of the reinforced ones and not the original design. BMW still will replace the original snowflake with the reinforced version. These wheels are the reinforced version due to the web along the main spoke from the hub to the rim as you can see in the two pictures below. You will find a picture of the recalled defective design in this article posted by Bob Fleischer, aka “Snowbum”:
The center hub is different on the left side and right side. The left side, which is the side with the locking nuts on the five Allan brake rotor bolts, has five webs from the bolt holes to the center hub. The right side hub is solid.
The left side rim of the front wheel has a number of markings. It does not have an arrow indicating the direction of rotation as the rear wheel does. The numbers that look like 11 digit part numbers are not part numbers, they are casting numbers. The markings indicate the rim is 2.15 inches x 19 inches. The left side of the wheel is the side with the five ribs around the center hub and is the side the brake rotor nuts are on.
Powder Coat The Wheels
Due to the intricate pattern of the cast snowflake wheel, I have them powder coated. It’s hard to get complete, even coverage spray painting them.
There are two schools of thought about powder coating: It’s not a good idea; It works well. One issue is what do you do when the powder coat gets chipped. I use matching paint to fill in the chip and that seems work well. The other thing to consider is powder coating on steel, when it chips, opens up a location for corrosion to start and if you neglect it, it will eat it’s way under the powder coat. Since I live in dry climate, and these are aluminum alloy wheels, corrosion is not the problem it would be with steel as aluminum oxide stops corrosion at the surface.
Since this bike is not a restoration, but a build staring from an RS and ending up with an RT, I’m taking some liberties with the paint and powder coat. I like the white wheels on the R65LS and I think white wheels lighten the stance of a bike. So, I had the wheels powder coated in matte white.
Refurbish Disk Brake Rotors
I use my small Harbor Freight bench top blasting cabinet to clean up the brake rotor carriers. They are pretty grungy and have some corrosion. I estimate that the air pressure is about 40 PSI so the glass bead is not too aggressive.
Very fine glass shards exit the cabinet and go everywhere. For that reason, I NEVER blast inside my shop. The cabinet is on casters and I roll it down the driveway and do my blasting there. I always wear an N95 face mask and eye protection. You do not want to breath fine glass into your lungs or get it into your eyes.
There is a mark on the back of the rotor carrier. “MIN 0.18”, that shows the minimum allowed rotor thickness; 0.18 inches (4.6 mm). I measured the rotor thickness and I have about 5 mm on the front rotors and close to 6 mm on the rear, to these have quite a few more miles left.
Next, I use 400 grit wet/dry paper and sand both faces of the rotor. I do this to remove any cooked on residue from the brake pads so the new pads will bed in correctly.
Then I use Q-tips and spray the end with a bit of brake cleaner. I clean out the inside of all the holes in the rotors. These accumulate grit, dirt and binder from the brake pads and this can foul new brake pads preventing them from bedding in correctly.
Install Disk Brake Rotors
I install the five Allen bolts, flat washers and lock nuts that secure the two disk rotors to the wheel. I make sure I return the rotor to the side of the wheel it came from as I labeled the rotors when I removed them. I torque the bolts to 17 FT-lbs,
On the rear wheel I install new safety strips with the tabs that lock the rear hex bolts and keep them from rotating. I torque the bolts to 17 FT-lbs.
Here are the wheels after powder coating and installation of the disk brake rotors. I think it’s a major improvement of the wheels from what I started with.
2020-05-04 Added note about wheel bearing replacement.
2020-06-04 Fix error in rear wheel bolt type-Hex rather than Allan.
Excellent timing, planned on doing this to my 84R80RT today!
I was planning on using mineral spirits to clean mine, and curious if you have an opinion on that. Saw a recent post on a list mentioning that, so hopefully that is correct to use. I have no parts washer or bead blast cabinets. Plan to just scrub with mineral spirits on surfaces and holes.
I don’t have an opinion. Let me know how it works.
For other folks that don’t have bead blast cabinets or other parts washing arrangements; Articles by Snowbum helped me along as well as these pics and videos. It takes a bit of fine grit wet-dry sandpaper, stronger solvent (mineral spirits), Q-tips, wiping with rags, cleaning with soap and water, and possibly all the above several times to get really clean. As Snowbum mentioned ‘clean all the holes’. Some residues and etc you can’t see on the discs and take your time doing it right so you don’t waste or foul up new pads. Obviously depends on your soil level. My rotors were luckily not too bad at all. A few rounds, a few lint free wipes, and final clean with brake cleaning spray (quick dry solvent), has them looking much better than they were. Thanks Brook, keep up the great work.
Brook- I didn’t see anything about the wheel bearings and seals? I’m presuming you removed them before Powdercoating?
I’m writing up the wheel bearing replacement material right now. Yes, I removed both the bearings and the rotors.
Do you think that it matters whether you put the bolts trough the right side or the left side when installing the front discs?
Thank you for all the detailed topics!
I always try to put the bike back together the way it was assembled at the factory. That way I won’t end up with a surprise.
My 1980 R100T is 42 years old, no telling how many people have tinkering with it. How would I know how the factory originally assembled it?
Read all my documentation on the rebuild of the 1983 R100RS conversion to an RT model. It’s very similar to your bike.
Brook, your articles have been a huge help to me on my BMW projects, Thank You. I just put a set of snowflakes on replacing the factory spokes on a custom R90/6 but when I took the front rotor off the original spoke wheels it had three of the shims (the thin circles with 5 holes that go under the bolt heads and nuts). Two were under the Allen heads on the right and one was under the nuts. Should it only have two or is the third supposed to go between the rotor and the wheel? I am almost certain the way they were installed was not correct.
From what I can see in the parts fiche, there are only two plates, one under the bolt head and the other under the nuts. The bolts should be 75 mm long. Is it possible someone installed longer bolts and added a plate to compensate for that?
I hope that helps.
Hi, Just wondering how you kept the powdercoat from the inside surface of the rear drive bevel? My coaters seem to get it everywhere so I’m somewhat nervous to give them my bare wheels. Did they grease it up so that the powdercoat didn’t stick?
I did nothing more than show them where they should not powder coat, and they did the rest.
I’ve used a couple different firms. Some ignore me, and I don’t do business with them anymore. This company pays attention and cares so they now are my exclusive supplier.
Awesome work as always Brook, your blog has been super helpful for my R100RT Resto. Quick question on the blasting of the disc carriers, did you mask the actual discs off or just carefully blast around the edge?
I’m pleased this material has helped you on your project.
I didn’t mask the disk off. But I did thoroughly clean it afterwards to be sure any glass dust was removed.
you said the rear wheel has allen bolts holding on thedisk. but the pictue shows hex head bolts and the lock tabs would not work with allens anyway. my bike has the same setup. have my bolts been changed?
My mistake on the bolts. I corrected that error in the text. Thank you for calling my attention to this.