The 1983 R80ST has a single front disk brake on the right side of the front wheel. It uses a Brembo caliper connected to a master cylinder and fluid reservoir built into the right handlebar control unit.  I repainted the caliper using black caliper paint.

Here is what the caliper looked like when I got the bike removed it from the bike.

Parts

All the parts for rebuilding the front caliper were provided free of charge by Euro MotoElectrics in support of my goal of auctioning this bike and donating all the proceeds to support the Motorcycle Relief Project.

I decided to replace the caliper pistons with new ones since the bike has sat for about 25 years. That said, the old pistons were in good condition.

Part #	Description	Qty
34 11 2 301 360	SET: REPAIR KIT, BRAKE PADS	1
34 21 1 237 234	SET: REPAIR BRAKE CALIPER – D=38MM	1
34 21 1 237 234-Piston	Brake Caliper Piston-38mm Available From Euro Motoelectrics	1
34 21 1 238 059	SET: MOUNTING PARTS – BREMBO	1
34 21 1 236 793	VENT SCREW	1

Video

Here is a short video summarizing the procedure. It is a mix of video from the 1983 R100RS and 1983 R80ST.

VIDEO: 1983 BMW R80ST Rebuild Front Brake Caliper

Brembo Caliper Rebuild For 1983 R100RS

I previously rebuilt the Brembo brake calipers on a 1983 R100RS. The rebuild procedure for the 1983 R100RS, and the parts, are the same as for the 1983 R80ST, so I will reuse documentation from the 1983 R100RS in this document, as appropriate.

• 34 BMW 1983 R100RS Disassemble, Inspect & Rebuild Brembo Brake Calipers

Disassemble Front Brake Caliper

Disassembly involves removing the plastic cover over the disk brake pads, removing the brake pad retaining clip and pads, unclamping the caliper halves, removing the dust seal, the piston and the piston seal.

• 34 BMW 1983 R100RS Disassemble, Inspect & Rebuild Brembo Brake Calipers
  • Disassemble Brake Caliper

On the 1983 R80ST, the 10mm bolts that clamp the caliper halves together would not come loose easily. I used some Kroil and some heat to try and get them to turn. In the end I had to use my air impact driver to get the bolts loose. They were completely rusted which is why they didn’t want to budge. The good news is the caliper halves are made from aluminum so they didn’t rust.

I did run a 10mm x 1.50 tap to clean the holes in the back caliper half and  also ran some round brass brushes through the holes to clean out rust and debris from the caliper bolts.

Here is the disassembled R80ST caliper.

Ensure Matting Surfaces On Caliper Halves Are Flat

The aluminum around the bolt holes commonly gets pulled up from the bolts which can cause brake fluid to leak from the passage that goes between the caliper halves. I use a large glass plate and 600 grit wet/dry paper to get the matting surfaces flat.

• 34 BMW 1983 R100RS Disassemble, Inspect & Rebuild Brembo Brake Calipers
  • Ensure Caliper Inside Mating Surfaces Are Flat

Paint Caliper

I painted the caliper halves with black caliper paint and after they had dried for a day, I baked them in the oven for 30 minutes at 200F to cure the caliper paint. I used the old bleed valve on one half and an M10 bolt on the other to hang the caliper halves for painting.

Rebuild Caliper

I used the grease packet supplied in the caliper rebuild kit to lubricate the square piston seal and the edge of the piston so it’s easy to install. Then I install the seal.

• 34 BMW 1983 R100RS Disassemble, Inspect & Rebuild Brembo Brake Calipers
  • Rebuild Caliper

Assemble Caliper Halves

I put a bit of the caliper grease on the small O-ring that seals the brake fluid passage between the caliper halves and then tighten the caliper bolts hand tight. I’ll torque the bolts after I get the caliper installed on the right fork slider.

• 34 BMW 1983 R100RS Disassemble, Inspect & Rebuild Brembo Brake Calipers
  • Assembly The Caliper Halves

NOTE:
I will  torque the caliper clamping bolts to 22 Ft-Lbs after I install the caliper on the lower fork slider. It’s easier to torque them when the caliper is installed.

Install Brake Pads, Retaining Clip Assembly, Pad Cover and Bleed Valve

Next I install the new brake pads (sintered), the retaining clips, and the brake pad cover and the new bleed valve. The bleed valve goes into the hole on the outside edge of the caliper.

• 34 BMW 1983 R100RS Disassemble, Inspect & Rebuild Brembo Brake Calipers
  • Install Brake Pads, Retaining Clip Assembly, Pad Cover and Bleed Valve

All Done

Here is what all done looks like.