This year and model has dual front disk brakes and a single rear disk brake. BMW switched to Brembo from ATE for their disk brakes in the 1981 model year, starting in September 1980, so this bike has Brembo brakes. This is what the bike looks like when I started removing the brake system.

This document covers removing the front and rear brakes (calipers, steel and rubber brake lines, master cylinders and brake fluid reservoirs) but not removing the disks and the front brake master cylinder which is integrated with the right side handlebar controls. I remove the disks when I remove the wheels and tires, and the right side handlebar control when I remove the steering components.

Remove Front Brake Assembly

This short video shows how the components of the front brake assembly are mounted.

VIDEO: 1983 BMW R100RS Front Brake Assembly

Drain Front Master Cylinder

The Brembo dual front brake system master cylinder and brake fluid reservoir are integrated into the right handlebar perch along with the throttle.

I start by opening the fluid reservoir on the handlebar and and removing the internal rubber diaphragm and the black plastic gasket on top of the diaphragm.

The fluid is the color of strong tea, which is not a good sign of frequent brake fluid changes. I remove the fluid with a syringe.

NOTE:
I took the lines apart starting at the master cylinder. But, I think it’s better if you start at the caliper so the brake fluid continues to drain out from the bottom and you work your way up to the top master cylinder. Your choice 🙂

Remove Master Cylinder Brake Line

Next, I remove the banjo bolt that secures the top of the rubber line to the master cylinder.

There are two copper washers that go on either face of the banjo bolt, or said differently, one goes against the master cylinder face and the other against the rubber brake hose face.

At the front of the brake line splitter-manifold is the rubber line from the master cylinder. I remove the fitting from the splitter-manifold.

Remove Steel Brake Lines From Splitter-Manifold

The splitter-manifold has two steel brake lines that feed the twin front disk brakes mounted on each side of the splitter-manifold. I remove these.

Then I unscrew the union between the rubber brake line and the splitter-manifold steel line to remove the steel line. The union has a rubber grommet in the hole. This grommet mounts in a slot in the center middle fairing panel to secure the brake line.

Remove Front Brake Line Splitter-Manifold

The front brake line splitter-manifold has the ignition control unit bolted to the top. I remove it. The back of the ignition control unit has a shiny metal pad which attaches to the top of the splitter-manifold. The splitter-manifold acts as a heat sink and requires heat sink paste to be applied to the shiny metal pad periodically for good heat transfer from the ignition control unit.

The ignition control unit is attached to the frame spine using a steel clamp that I remove.

Remove Front Caliper Steel Brake Line & Bleed Screw

Next, I disconnect the caliper steel brake line from the lower rubber line at the bracket mounted to the rear fork brace bolt. This connection is similar to the upper union and has a rubber grommet that fits inside the hole in the bracket.

The steel and rubber line fittings fit inside a rubber grommet in the hole of the brake line bracket.

Then I remove the bleed screw and steel brake line on both front calipers.

Remove Front Caliper and Brake Line Bracket

The front caliper is secured to the front fork slider with two Allan head bolts. The other two bolts in the caliper are used to assemble the two halves.

Once the two bolts are removed, the caliper slides off the disk.

The disk pads look fairly new.

This is the Brembo part number stamped into the back of the caliper.

The front caliper brake line union bracket is secured by the rear fork brace Allan bolt underneath the nut. I remove the rear lock nut and remove the bracket which is very rusty.

Remove Rear Brake System

The Brembo single disk rear brake system has its own master cylinder mounted on the inside of the right hand muffler bracket next to the swing arm. The fluid reservoir is attached to the frame battery box bracket with a steel strap. Here is a short video showing how the rear master cylinder and mounting bracket, and the rear brake pedal are mounted.

VIDEO: 1983 BMW R100RS Master Cylinder Mounting

NOTE:
Due to battery acid leaks, there was a lot of rust on the master cylinder bracket and the special pin that secures the top of the brake pedal to the master cylinder plunger linkage. I could not get the special pin to come out, so I had to remove the master cylinder on the bracket with the rear brake pedal attached which is harder to do, but can be done.

The rear caliper is on the left side of the bike with a steel brake line from the outlet of the master cylinder connecting to a rubber brake line that attaches to the rear brake caliper. The caliper mounts to a plate that attaches to the rear axle and is secured with a brake stay, or torque rod, to a bracket on the bottom of the swing arm. Here is a short video showing how these are mounted.

VIDEO: 1983 BMW R100RS Rear Caliper Mounting

Detach Rear Master Cylinder Fluid Reservoir and Drain

The rear master cylinder fluid reservoir is secured using a metal strap that attaches tothe top, right rear battery box rubber isolation damper. This damper has one longer thread than the other four to secure the rear fluid reservoir mounting strap.

After I remove it, I open the top and pour the fluid out of the reservoir.

Remove Rear Brake Pedal Assembly

The rear brake pedal is attached to the frame with a long bolt through a boss welded to the frame. There is a lock nut and washer on the back.

The bolt and other hardware on this bike is not stock. Someone tried to fix the wobble in the brake pedal using a longer shoulder bolt, a metal cap and some aluminum can for shim. Brake pedal wobble is caused by lack of lubrication of the bolt that fits inside a bushing. The bushing and bolt wear and loosen up causing more wear. I will replace the bushing and get the proper hardware.

The brake pedal is secured to the master cylinder plunger linkage with a special pin. In theory, you push down on the retaining clip that fits over the bushing of the master cylinder linkage, rotate it 90 degrees and then pull the pin out. But mine is badly rusted so I will have to remove the master cylinder and bracket with the rear brake pedal attached.

Remove Rear Master Cylinder & Bracket

At the rear of the master cylinder there is a spring that attaches to a hole in the rear muffler bracket. This is the brake pedal return spring that I remove.

The steel brake line from the master cylinder to the rear brake caliper attaches to the rear of the master cylinder and I remove it.

The master cylinder attaches to a bracket. The bracket is secured at the rear by the rear muffler bracket bolts. To get the bracket to slide off the muffler bracket, I have to remove the exhaust hanger bracket on the rear engine mount to free the muffler so I can push it down to free the rear of the master cylinder bracket.

The front of the master cylinder bracket is secured with an Allan bolt to bracket welded to the swing arm. I remove it.

Here is how the front bracket mounting hardware is attached.

Here is the master cylinder and bracket and the rear brake pedal assembly removed from the bike.

I use a punch to drive the rusted special pin out of the master cylinder linkage so I can remove the rear brake pedal.

At the top of the rear brake pedal is a bolt and nut that adjust when the rear brake light switch closes.

The hose from the rear brake fluid reservoir to the master cylinder is frayed so I will replace it.

The end of the hose is attached to the master cylinder with a use-once hose clamp.

Remove Rear Master Cylinder From Bracket

I remove the two Allan bolts that secure the rear master cylinder to the bracket. The holes in the bracket are tapped.

Remove Rear Disk Caliper

The rear disk caliper is on the left side and mounts with two bolts, one at the bottom of the caliper and one at the top, to a plate. The brake plate is secured around the axle and has a torque arm that attaches it to a bracket welded to the bottom left side of the swing arm. There are also two more bolts in the caliper, but these secure the two halves together and I don’t remove them. I remove the brake plate and torque arm when I remove the rear wheel.

I remove the two bolts and slide the caliper off the rear disk rotor.

Remove Brake Lines Between Rear Master Cylinder and Caliper

The caliper has a rubber brake hose attached to it that flexes as the swing and rear wheel move up and down. The other end of the rubber brake hose fits in a bracket and a union between it and the steel brake line coming from the master cylinder.

After I remove the steel line from the rubber hose at the bracket union, I unscrew the rubber hose from the caliper. The hose is cracked so it’s time to replace it.

The back of the caliper has a Brembo part number stamped into it.

The brake pads don’t look too worn, but the pad on the left is worn more than the one on the right.

Lastly, I remove the steel brake line and the bracket. The bracket has a rubber grommet in the hole and a square nut welded to the back of the bracket.

It takes some “dancing” to extract the brake line as one end has to clear the swing arm and the other has to clear the rear of the frame as shown in the video above and in this excerpt.

Here is how the bike looks now. I will remove the disk rotors when I remove the wheels and tires.