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Rebuilding BMW Brake Calipers

Pelican Technical Article:

Rebuilding BMW Brake Calipers


2 hours2 hrs






Brake cleaner, 6mm & 7mm Allen wrench, cellophane, baggies, zip-ties, small flatblade screwdriver, 1-inch block of wood, compressed air line with needle style air chuck, torque wrench, Scotch Brite pad, vise-grips, 16mm socket and 1/2-inch driver, rubber mallet, large C-clamp, oil pan, WD40, turkey baster, needle nose pliers, rubber mallet

Applicable Models:

BMW E30 318i Coupe/Conv (1984-92)
BMW E30 318i Sedan (1984-92)
BMW E30 318is Coupe (1984-92)
BMW E30 325 Coupe (1986-88)
BMW E30 325 Sedan (1986-88)
BMW E30 325e/es/is/iX Coupe (1984-93)
BMW E30 325e/i/iX Sedan (1984-93)
BMW E30 325i Coupe/Conv (1984-93)
BMW E36 318i Convertible (1992-99)
BMW E36 318i Sedan (1992-99)
BMW E36 318is Coupe (1992-99)
BMW E36 318ti Hatchback (1992-99)
BMW E36 323i Convertible (1998-99)
BMW E36 323is Coupe (1998-99)
BMW E36 325i Convertible (1992-95)
BMW E36 325i Sedan (1992-95)
BMW E36 325is Coupe (1992-95)
BMW E36 328i Convertible (1996-99)
BMW E36 328i Sedan (1996-99)
BMW E36 328is Coupe (1996-99)

Parts Required:

Brake caliper rebuild kit

Performance Gain:

BMW brakes that stop short and true as if they were new

Complementary Modification:

Replace the brake pads, replace the rotors, replace the brake fluid and bleed the brakes
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If your car is pulling to one side when braking, you might have a sticky caliper that needs rebuilding. The rebuilding process is actually a lot simpler than most people think. Rebuilding involves removing the caliper, cleaning it, and then reinstalling all of the components, along with new seals. Removing the caliper is often the most difficult part of the task.

First, jack up the car (see our article on jacking up your BMW). Then refer to Project 57 for details on removing the caliper from around the brake disc. Moving on, Project 56 will guide you in disconnecting the brake line from the caliper. Once you have the caliper free and clear from the car, take it over to your workbench, and begin the disassembly process.

Start by removing the piston from the calipers. Using a small screwdriver, remove the dust boot that surrounds the piston. Place a small block of wood in the center of the caliper to prevent the pistons from flying out of the caliper. Then blow compressed air through the caliper bleeder hole to force the piston out of its chamber. Start slowly, and gradually increase pressure until the piston reaches the block of wood. Make sure the piston doesn't come all the way out of its chamber. After the piston is far enough out, you should be able to grip it with your fingers. Be careful when working with compressed air, as it is more powerful than it appears and can make the pistons fly out of the caliper unexpectedly.

Using a rag to protect the sides of the pistons, carefully remove them both from the caliper with your hands or a large pair of Vise-Grips. Don't touch the sides of the pistons with any metal tools, which may scratch their surfaces.

If the piston is frozen, more radical methods of removal may be necessary. Using a block of wood, pound the caliper half on the block of wood until the piston begins to fall out. If the piston starts to come out and then gets stuck, push it back in all the way and try again. Eventually, the piston should come out of the caliper half. Another method is to use the car's brake system to release the pistons. Reconnect the caliper to the car, and have an assistant pump the brakes to force out the piston.

Once the piston has been removed from the caliper, carefully clean both the inside and outside of the caliper with brake cleaner or another appropriate solvent. Blow out all of the passages with compressed air. If possible, let the whole assembly sit in parts cleaner overnight. If the piston or its cylinder is badly rusted or pitted, replace the caliper. A little bit of surface rust is okay but should be polished off with a coarse cloth or Scotch-Brite. Thoroughly scrub out the inside of the cylinder and outside of the piston so they are perfectly clean.

After the caliper and piston have been cleaned and dried, coat the cylinder and piston with silicone assembly lube. If you don't have this silicone assembly lube handy (available from, coat the entire assembly with clean brake fluid. Be careful not to get any lube or brake fluid on the dust boot.

Insert the new piston seal inside the caliper piston groove. It should fit smoothly in the groove, yet stick out slightly. Wet the seal with a little brake fluid. Now install the dust boot inside-out onto the piston, so the edge of the boot hangs out toward the area where the piston contacts the brake pad. Then, insert the piston slightly into the caliper. It should slide in easily, but make sure it doesn't go in crooked. Wrap the dust boot around the outer edge of the caliper, and then push the piston into the caliper.

As the piston reaches the internal O-ring, you will encounter some resistance. Make sure the piston is pushed in and doesn't become cocked as you insert it. If you have trouble inserting the piston into the caliper, softly tap it with a plastic hammer, or use a small piece of wood to compress the piston into its home position in the caliper housing.

Now install the brake pads (Project 51) and remount the caliper onto the car. Bleed the brake system (Project 50), and you should be good to go. Of course, carefully test the brakes on the car before you do any significant driving.

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Figure 1

Rebuilding calipers is a lot easier than you might think. The basic principle involves tearing apart the caliper, cleaning it, and then reinstalling the pistons with new seals and clips. Professionally rebuilt calipers, like this one, are usually sandblasted and plated so they return to their original gold color. Rebuilding your calipers may solve a lot of mysterious brake problems you've been experiencing. Because rebuilding seems difficult, it's usually the last project tackled when overhauling the brakes. Another option is to purchase rebuilt calipers and mount them on your car.

Figure 2

Replace the inner piston seal, which keeps brake fluid from leaking out past the cylinder. Also, clean the inside of the cylinder of dirt, debris, and corrosion. Don't scratch the inside of the caliper cylinder while you are working on it, or the caliper may leak when you reassemble it.

Comments and Suggestions:
Marc Comments: I recently replaced the seal and boot of the rear brakes on a ‘98 E36 Compact. I am a fairly experienced DIY mechanic, but spent over an hour fiddling with the dust boot. Aarghh This boot has to be fitted inside the cylinder, but it is near impossible to get it in there once the piston is in. How I did it: fit the boot over the piston as close to the bottom as yo can get it. Then extend the boot over the bottom of the piston, so that the lip that should fit into the groove of the cylinder hangs out free from it. Secure the top of the boot to the piston with a tie wrap, otherwise it will slide off. Now you can put the lip inside the groove. Then carefully insert the piston, remove the tiewrap and you’re done. Be sure to lube everything up good, otherwise the piston will not slide into the boot. I kept thinking that there must be some handy trick to do this, but couldn’t come up with anything better. Anyone?
November 28, 2017
  Followup from the Pelican Staff: In the few times I have done this, I install the piston with seals. Then install the dust boot. I install boot onto caliper first, then use a small plastic tool to install it onto the piston. - Nick at Pelican Parts  
aksispd Comments: After rebuild of the caliper the car still pulls to the right and there is a rumbling noise. What else can it be?
October 3, 2017
  Followup from the Pelican Staff: bad: tire, wheel bearing, front suspension component. - Nick at Pelican Parts  
Brake rebuilding novice Comments: Would it be ok to rub the inside of the cylinder with very fine emery paper?
October 10, 2015
  Followup from the Pelican Staff: No, BMW has coated cylinders. Try a scotch-brite pad with warm soapy water. - Nick at Pelican Parts  
Dan Comments: Hi, do you have any info on how to fit the dust boot to the caliper when it has a metal ring inside? This one on my E46 has no groove around the piston hole in the caliper and the boot has no lip, the boot is just a friction fit and requires a "special tool".
February 14, 2014
  Followup from the Pelican Staff: No I don't. I replace the calipers when there is a problem. - Nick at Pelican Parts  
rjteeter Comments: Any info on where to get new caliper pistons?
October 8, 2010
  Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need.
- Nick at Pelican Parts
bill Comments: Thanks for this article. On my 95 m3 the left rear caliper has a bad dust boot. I'm going to try to rebuild it
February 13, 2010
  Followup from the Pelican Staff: Let us know how it goes, Give our parts specialists a call at 1-888-280-7799 and they can help figure out which part or repair kit you need.
- Nick at Pelican Parts

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Page last updated: Fri 1/19/2018 02:04:59 AM