I’m converting this RS model to a RT. The only difference in the brake system is the length of the hose from the front master cylinder to the front brake line manifold underneath the gas tank (RT: Part# 34 32 1 241 565; RS: Part# 34 32 1 241 564). Since the RT handlebars are wider, that hose is longer. The rear brake system is the same on both the RS and RT models.

I previously rebuilt the two front and one rear calipers and rebuilt the rear master cylinder. The front master cylinder was so badly corroded that I replaced it along with the entire right handlebar perch. I also installed the three disk brake rotors on the newly powder coated wheels. You can read about how I did that work here.

• 34 BMW 1983 R100RS Disassemble, Inspect & Rebuild Brembo Brake Calipers
• 34 BMW 1983 R100RS Disassemble, Inspect & Rebuild Master Cylinders
• 34 BMW 1983 R100RS Remove, Refinish, Install Disk Brake Rotors

Here is the link to how I install the rear brake system.

• 34 BMW 1983 R100RS Install Rear Brake System

Parts

I opted to use the mechanical front brake switch that mounts in the right perch instead of the original brake fluid pressure switch that mounts on the rear of the front brake manifold under the gas tank. The hole in the pressure switch can trap an air bubble making it more difficult to bleed the brakes.

I plugged the rear hole in the front brake line manifold where the front brake light pressure switch mounts.  McMaster-Carr sells a plug with copper crush washer that’s perfect for this.

Here is a list of brake system parts I replaced in the front brake system not including the parts I replaced when I rebuilt the front calipers and replaced the front master cylinder. I found cracked hoses so I replaced them. I also replaced the steel brake lines due to the amount of corrosion I found in the front master cylinder in case the lines also had started to rust. The last item in the list below is the plug I put into the brake switch hole of the front brake line manifold.

Part #	Description	Qty
34 32 1 241 565	BRAKE HOSE MC – L=425MM (from 09/80)	1
34 32 1 235 736	BRAKE HOSE – L=362MM (from 09/80)	2
34 32 1 241 957	BRAKE PIPE (from 09/80), Upper	2
34 32 1 235 671	BRAKE PIPE LEFT (from 09/80), Lower	1
34 32 1 235 672	BRAKE PIPE RIGHT (from 09/80), Lower	1
34 32 1 233 159	GROMMET (from 09/80) Hose to Pipe	4
07 11 9 963 072	GASKET RING – A10X13,5-CU (from 09/80) Banjo Bolt	2
McMaster-Carr     Part# 3600N3	Low Pressure 316 Stainless Steel Threaded Plug With Hex Drive, M10x11x1.0	1

Tools

I use an “Air Zapper” vacuum pump to pull brake fluid from the brake fluid reservoir through the bleed hole in the caliper. This tool does a very good job removing air from the system.

Video

This video is a summary of the front brake system installation procedure:

VIDEO: 1983 BMW R100RS/RT Install Front Brake System

Front Brake System Components

The picture below shows the front brake system components except for the front brake calipers. I show the pipes and hoses that go to one caliper only for clarity.

Each caliper has an “S” shaped steel brake line that screws into one of the threaded holes in the caliper. The other end of the “S” line screws into one end of the caliper brake hose. Each end of the caliper brake hose fits into a rubber grommet. The other end of the caliper hose screws into the steel caliper manifold line which attaches to one side of the front brake line manifold that attaches to the spine tube under the gas tank using the manifold clamp. The master cylinder hose attaches to the right perch with a banjo fitting and a banjo bolt. The other end screws into the center hole of the front brake line manifold.

I painted the brake calipers blue to pay tribute to the 1977, first year RS, that had blue anodized calipers. The red tape covers the caliper clamping bolts reminding me I have not torqued them yet.

Modify Front Brake Line Manifold

The original front brake line manifold that is mounted on the spine tube under the gas tank had the front brake switch attached to it. It’s a pressure switch that turns on the rear brake light when the front brake lever is pulled.

Another option is to use the small switch that mounts on the right handlebar perch and is activated as the brake lever rotates to turn on the brake light.

This requires adding the proper length (RT handlebars) sub-harness to connect the switch to the main wiring harness. I opted to use this switch instead of the brake fluid pressure switch as the hole in the switch can trap an air bubble making it hard to bleed the front brakes completely.

But, if the pressure switch is removed, then I need to plug the hole in the rear of the manifold the switch screws into. Tom Cutter at Rubber Chicken Racing Garage recommended I use a stainless steel plug with copper washer available at McMaster Carr.

I mount the stainless plug using blue Loctite and the included copper washer to seal off the front brake pressure switch hole.

Install Brake Calipers

I build the front brake system from the bottom up to the front brake manifold starting with the caliper.

Clean Disk Brake Rotors

Before I mount the calipers I use brake cleaner to remove oil, grease and grunge from the disk brake rotors. I previously cleaned out all the vent holes in the disks with a Q-tip and brake cleaner to remove the built-up junk that collects in the holes as well as cleaned the disk faces. But it’s been awhile since I did that and I want to be sure the new brake pads aren’t fouled by garbage that may have gotten on the disks while I’ve been working on the bike. I want the pads to bed into the disk correctly and not be fouled with debris, oil or dirt.

I use a clean blue shop towel folded in half, wet it with brake cleaner, and then fold it over the disk while I rotate the wheel. I continue to clean the disk rotor this way with clean shop towels until I don’t see any more grunge on the towel.

Install Caliper Brake Line Bracket

A caliper brake hose bracket mounts on the rear fender brace bolt on the inside of the brace with the lock nut on top of it on each side. The right and left brackets are different. One rubber grommet fits in the hole in the bracket. The grommet has two different faces: The shallow face goes against the hex nut of the caliper brake hose and the deep face points toward the steel brake line fitting. I leave the bracket loose so I can align it with the caliper steel brake line when I install the caliper.

I install the caliper brake hose into the hole in the bracket before I mount the bracket.

Mount Caliper And Attach Brake Line & Hose

I install the “S” shaped steel brake line in the outer hole of the caliper. I finger tighten the fitting loosely into the caliper for now so I can align the brake line fitting when I screw it into the caliper brake hose. The bleed valve fits in the hole closest to the wheel.

I slide the caliper over the disk while positioning the caliper steel brake line fitting on the end into the grommet on the caliper brake hose bracket.

I torque the caliper mounting bolts to 20 FT-Lbs. After I do that, I remove the red tape on the caliper clamp bolts and torque them to 22 FT-Lbs.

I tighten up the fitting on the steel brake line that screws into the caliper brake hose and the fitting that goes into the caliper.  I tighten the lock nut on the rear bolt securing the fender brace and caliper brake hose bracket to the fork slider.

Mount Front Brake Manifold, Attach Brake Lines

After I have both front brake calipers, steel brake lines and hoses mounted, I attach the front brake manifold to the spine tube. First I screw the master cylinder brake hose into the front hole of the manifold and tighten the fitting.

The large hose clamp fits in the front slot of the starter relay bracket and the screw for tightening the clamp goes on the right side of the frame. I leave the hose clamp loose so I can align the manifold with the fittings on the steel brake lines while I tighten the fittings.

I route the manifold steel brake line through the frame next to the down tube. I screw the upper steel brake line fitting into the hole on the side of the manifold. Before I screw the lower fitting into the caliper brake hose, I install the rubber grommet on the brake hose fitting. This grommet fits into a hole in the fairing panel.

I attach the end of the master cylinder hose that has the banjo fitting with the banjo bolt on the end of the master cylinder. The steel line on the end of the banjo fitting has an angle that points toward the frame. I put a copper crush washer on each face of the banjo fitting and tighten the banjo bolt, but I don’t over tighten it.

Here’s the front brake system after installing it.

Bleed Front Brake System

I remove the cover from the front brake fluid reservoir and put fresh DOT 4 brake fluid into the front reservoir.

NOTE:
Do not use an old open can of DOT 4 brake fluid. It starts absorbing water from the air immediately after it’s opened and water corrodes the internal components of the brake system. Brake fluid is cheap compared to brake system parts.

I close the bleed valves on both calipers. I pump the front brake lever and eventually I see bubbles coming out of the the master cylinder into the reservoir; bigger bubbles from the large entry hole and little ones from the small fluid return hole. I continue to pump the lever to help push fluid into the master cylinder and into the lines which evacuates a lot of the air in the system.

NOTE:
I want to be sure the small return hole on the master cylinder is not blocked and if I see small bubbles coming out of that hole, I know it is open.

When there aren’t many bubbles returning to the reservoir, I attach my Air Zapper to bleed the system by pulling brake fluid out of the bleed valve on one caliper at a time. The hose with the rubber boot goes over the nipple on the caliper bleed valve. The other plastic line goes to the port on the vacuum pump.

I make sure the fluid reservoir is full, turn on the Air Zapper, open the bleed valve a quarter turn and watch the fluid come out with air bubbles. When it looks like just fluid is coming out, I close the bleed valve. Before I repeat this procedure on the other caliper, I refill the reservoir before I turn on the Air Zapper.

The front brake lever feels solid so I think I have all the air out of the system. But as insurance, I like to use a small bungee cord wrapped around the front brake lever to pull it about half way to the handlebar to put pressure on the system. I leave it that way over night. Any small air bubbles trapped in the system will migrate up the brake lines to the master cylinder and exit into the fluid reservoir. I’ve had good luck with this technique particularly when I couldn’t get all the air out of a brake system.

All Done.