34 BMW 1983 R80ST Rebuild Front Brake Caliper

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.

As Found: Front Brembo Disk Brake Caliper And Missing Brake Rotor

As Found: Front Brembo Disk Brake Caliper And Missing Brake Rotor

Brembo Front Brake Caliper With Crusty Looking Brake Pads

Brembo Front Brake Caliper With Crusty Looking Brake Pads

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.

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.

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.

After Washing Caliper

After Washing Caliper

Brake Pads Are Looking Old

Brake Pads Are Looking Old

Kroil Penetrating Oil For Loosening Stuck Caliper Bolts

Kroil Penetrating Oil For Loosening Stuck Caliper Bolts

I Had To Get Out The Big Gun, An Air Impact Wrench, To Remove The Rusted Caliper Clamping Bolts

I Had To Get Out The Big Gun, An Air Impact Wrench, To Remove The Rusted Caliper Clamping Bolts

Caliper Bolts Are Very Rusty

Caliper Bolts Are Very Rusty

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.

Use 10x1.50 Tap To Clean Threads in Back Half Of Caliper

Use 10×1.50 Tap To Clean Threads in Back Half Of Caliper

Here is the disassembled R80ST caliper.

After Removing Caliper Bolts

After Removing Caliper Bolts

Brake Pad Mounting Hardware

Brake Pad Mounting Hardware

Cover & Brake Pads Removed

Cover & Brake Pads Removed

Caliper Pucks Removed

Caliper Pucks Removed

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.

Paint Marks Added To Caliper Mating Surfaces

Paint Marks Added To Caliper Mating Surfaces

After Sanding On Glass Plate To Ensure Caliper Mating Surfaces Are Flat

After Sanding On Glass Plate To Ensure Caliper 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.

Mating Surface & Puck Hole Masked Off

Mating Surface & Puck Hole Masked Off

Ready To Hang For Painting

Ready To Hang For Painting

Painted Brembo Calipers Drying

Painted Brembo Calipers Drying

Repainted Brembo Calipers

Repainted Brembo Calipers

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.

Brembo Caliper Rebuild Parts Including New Pucks

Brembo Caliper Rebuild Parts Including New Pucks

Square O-ring & Puck Installed

Square O-ring & Puck Installed

Dust Cap Installed

Dust Cap Installed

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.

Brake Fluid Passage O-ring With Caliper Grease Installed In Hole

Brake Fluid Passage O-ring With Caliper Grease Installed In Hole

Caliper Clamping Bolts Installed Finger Tight

Caliper Clamping Bolts Installed Finger Tight

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.

New Sintered Brake Pads And Mounting Hardware

New Sintered Brake Pads And Mounting Hardware

New Brake Pads Installed In Caliper

New Brake Pads Installed In Caliper

New Caliper Bleed Valve

New Caliper Bleed Valve

All Done

Here is what all done looks like.

Brembo Front Caliper After Rebuilding

Brembo Front Caliper After Rebuilding

Brembo Front Caliper After Rebuilding

Brembo Front Caliper After Rebuilding

Brembo Front Caliper After Rebuilding

Brembo Front Caliper After Rebuilding

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