34 BMW 1983 R100RS Remove, Refinish, Install Disk Brake Rotors

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.

NOTE:
I also removed the wheel bearings before having the wheels powder coated. There is a separate document about how to replace the wheel bearings.

Parts

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.

Part #                       Description                                                      Qty
34 21 1 235 843  SECURING PLATE 1
34 21 1 235 844  SECURING PLATE 1

Video

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 Allan 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.

Rear Wheel Left Side

Rear Wheel Left Side

Rear Disk Brake Rotor Mounts To Wheel With Five Bolts Secured By Tabs On Retaining Strips

Rear Disk Brake Rotor Mounts To Wheel With Five Bolts Secured By Tabs On Retaining Strips

Tab On Bolt Retaining Strip Bends Up Against A Bolt Face To Keep It From Backing Out

Tab On Bolt Retaining Strip Bends Up Against A Bolt Face To Keep It From Backing Out

Tab On Bolt Retaining Strip

Tab On Bolt Retaining Strip

I use a screw drive and hammer to flatten the metal tabs on the strips.  Then I remove the five bolts.

Flattening Tab On Bolt Retaining Strip

Flattening Tab On Bolt Retaining Strip

Rear Disk Brake Rotor Bolt Detail

Rear Disk Brake Rotor Bolt Detail

Rear Disk Brake Rotor Mounting Hardware Detail

Rear Disk Brake Rotor Mounting Hardware Detail

The brake rotor and it’s hub pull off the center hub of the wheel.

Pull Rear Disk Brake Rotor Up Off The Hub

Pull Rear Disk Brake Rotor Up Off The Hub

Rear Disk Brake Rotor Removed

Rear Disk Brake Rotor Removed

Rear Disk Brake Rotor Hub with Wheel Bearing

Rear Disk Brake Rotor Hub with Wheel Bearing

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.

Rear Wheel Right Side

Rear Wheel Right Side

Rear Wheel Left Side

Rear Wheel Left Side

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.

Rear Wheel Left Side Markings

Rear Wheel Left Side Markings

Rear Wheel Left Side Markings

Rear Wheel Left Side Markings

Rear Wheel Left Side Markings

Rear Wheel Left Side Markings

Rear Wheel Left Side Markings

Rear Wheel Left Side Markings

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.

Use Wood Blocks To Protect Front Rotors From Damage When Working On The Wheel

Use Wood Blocks To Protect Front Rotors From Damage When Working On The Wheel

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.

Left Side Disk Brake Rotor Has Locking Nuts

Front Left Side Disk Brake Rotor Has Locking Nuts

Right Side Disk Brake Rotor Has Allan Head Bolts

Front Right Side Disk Brake Rotor Has Allan Head Bolts

I remove the five bolts. The disc brake rotors pull off the hubs the same way the rear brake rotor did.

Front Disk Brake Rotor Bolt Detail

Front Disk Brake Rotor Bolt Detail

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.

Left Side Disk Brake Rotor Hub Detail

Left Side Disk Brake Rotor Hub Detail

Right Side Disk Brake Rotor Hub Detail

Right Side Disk Brake Rotor Hub Detail

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.

Front Wheel, Left Side Markings

Front Wheel, Left Side Markings

Front Wheel, Left Side Markings

Front Wheel, Left Side Markings 2.15 x 19 Inch Rim

Front Wheel, Left Side Markings

Front Wheel, Left Side Markings

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.

NOTE:
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.

BEFORE: Front Wheel Paint Is In Bad Shape

BEFORE: Front Wheel Paint Is In Bad Shape

BEFORE: Rear Wheel Right Side

BEFORE: Rear Wheel Right Side

AFTER: Powder Coated Wheels in White

AFTER: Powder Coated Wheels in White

AFTER: Front Wheel White Powder Coat

AFTER: Front Wheel White Powder Coat

AFTER: Rear Wheel Powder Coat

AFTER: Rear Wheel Powder Coat

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.

DANGER:
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.

Rotor Carrier Front Side Grunge

Rotor Carrier Front Side Grunge

Rotor Carrier Back Side Grunge

Rotor Carrier Back Side Grunge

Front Side Carrier After Bead Blasting at 40 PSI

Front Side Carrier After Bead Blasting at 40 PSI

Rear Side of Carrier After Bead Blasting at 40 PSI

Rear Side of Carrier After Bead Blasting at 40 PSI

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.

Minimum Rotor Thickness Marked On Back of Rotor Carrier-0.18 Inches (4.6 mm)

Minimum Rotor Thickness Marked On Back of Rotor Carrier-0.18 Inches (4.6 mm)

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.

Sanding Rotor Faces with 400 Wet/Dry To Remove Baked On Brake Pad Grunge

Sanding Rotor Faces with 400 Wet/Dry To Remove Baked On Brake Pad Grunge

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.

Use Q-tip Wet With Brake Cleaner To Clean Out Holes

Use Q-tip Wet With Brake Cleaner To Clean Out Holes

Grunge Inside Rotor Hole

Grunge Inside Rotor Hole

Dirty Q-tips After Cleaning The Holes In One Rotor

Dirty Q-tips After Cleaning The Holes In One Rotor

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,

Torque Rotor Bolts to 17 FT-Lbs

Torque Rotor Bolts to 17 FT-Lbs

Refurbished Rotors Installed on Powder Coated Front Wheel

Refurbished Rotors Installed on Powder Coated Front Wheel

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.

New Safety Strips For Securing Rear Disk Brake Rotor Bolts In Wheel

New Safety Strips For Securing Rear Disk Brake Rotor Bolts In Wheel

Torque Rotor Bolts to 17 FT-Lbs

Torque Rotor Bolts to 17 FT-Lbs

Bending Safety Strip Tab Over Bolt Head

Bending Safety Strip Tab Over Bolt Head

Safety Strip Tab Bent Over Edger of Bolt Head

Safety Strip Tab Bent Over Edger of Bolt Head

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.

Brake Disk Rotors Installed On Newly Powder Coated Wheels

Brake Disk Rotors Installed On Newly Powder Coated Wheels

Revisions

2020-05-04  Added note about wheel bearing replacement.

11 thoughts on “34 BMW 1983 R100RS Remove, Refinish, Install Disk Brake Rotors

  1. 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.

      • 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.

  2. Brook- I didn’t see anything about the wheel bearings and seals? I’m presuming you removed them before Powdercoating?

    • Hi Steve,

      I’m writing up the wheel bearing replacement material right now. Yes, I removed both the bearings and the rotors.

      Best.
      Brook.

  3. Hi Brook,

    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!

    Best regards,

    Erwin

    • Hi Erwin,

      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.

      Best.
      Brook.

  4. 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.

    Thanks Jeff

    • Hi Jeff,

      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.

      Best.
      Brook.

  5. 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?
    Thanks,
    Tom.

    • Hi Tom,

      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.

      Best.
      Brook.

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