Rebuilding E36 M3 Calipers

The brakes on the M3 Sedan have been untouched up until now, other than my replacing of the rotors a little while ago, so it was time for a good once over and caliper rebuild.

During my work on the rear suspension, I noticed the caliper dust boots had slightly pulled out. I’m sure the slider bushings need replacing as well.

I have an upcoming track day at Road Atlanta, so I also wanted to swap out the EBC Blue pads that came with the car for a set of PFC 08s I had previously used on the M Coupe. I wasn’t very impressed with the EBC Blue, which stopped the car well once up to temps but had poor initial bite and were a bit noisy. I plan to keep the PFC 08’s on for the track weekend, then swap in some PFZ Z-rated for daily use (same as the M Coupe.)

I also noticed that the EBC pads had grooved the rotors pretty badly, so that would need addressed as well. The pads were also tapered, the rears more so and also worn down.

So the brakes came off the car. Since I was removing the lines at their connection to the hard line, I needed to plug the fitting or otherwise risk draining the system of brake fluid. And believe me, you don’t want to try bleeding the entire system if you can help it! I found that the little rubber caps used to protect bleed nipples worked perfectly for also plugging the double flare of the hard line. Good to keep a handful of these around.

With the calipers off and the mounting bracket removed, the next step was to dislodge the piston. This is done by using a blast of compressed air. You’ll need an air-gun with a rubber tip to seal up against the brake line (or the hole in the caliper if the lines are removed.) Get a large bucket or tray to place the caliper into, as you’ll get a nice blast of brake fluid when doing this (don’t forget your eye-pro). You’ll also want to use a piece of wood to cushion the piston when it exits the cylinder, as it comes out with some force. Be prepared for the loud “pop” as well!

With the piston out, next comes the piston seal. A dental pick works well to remove the seal from its recessed groove in the cylinder wall. Take care that you don’t gouge the wall, which would create issues down the road. With the calipers completely disassembled, I took them over to the parts cleaner for a good scrubbing. I wasn’t looking to get them show-room clean, just remove the years of brake dust and road grime buildup. After that I laid them out in the sun to dry off the kerosene.

The pistons had quite a bit of surface rust on their exteriors (not the portion inside the cylinder thankfully), so I gave them a 24hr dunk in some Rust Eliminator. With all the parts now dried, I gave all the pieces a good blast of brake cleaner, followed by some compressed air to make sure there weren’t any remaining particulates or kerosene residue.

Before assembling the calipers, the seals and dust boots must be lubricated. Now my first choice would have been some ATE assembly lube, but it’s not available in the US for whatever reason. Don’t be fooled into use the ATE Plasti-Lube, which is intended for external use, as an “anti-squeal” lubricant. It is a mineral based (petroleum) lubricant and can cause rubber seals to swell, which could create serious issues like a piston that won’t retract. You need a silicone based lubricant made for use on rubber. Many folks recommend Dow 111 or similar, such as Sil-Glyde, which can be found at NAPA.

I picked up a tube for this purpose, using it to grease the seal prior to installation. You don’t need a heavy coat, don’t glob it on the cylinder wall. It’s not going to be as heat resistant as brake fluid, it’s just used to lubricate the seals and boots for installation purposes.

Now for the most difficult part of the job; getting that dust boot seated. For this step I went to the interwebs, specifically YouTube for any tips or tricks. I had read and seen a few suggestions to seat the boot in its groove, insert the piston, then just push the boot into the caliper with a screwdriver or other blunt instrument. Please do not do this! You will more than likely damage the boot and even if you are lucky you will have a hell of a time getting the boot seated properly. (Tip: Buy an extra set of front and rear seals!) Watch the video below for a better understanding (note the big tube of the previously mentioned ATE assembly lube):

As you can see the seal went in with ease. It took me a little practice, but after the first one they all went together like butter. The key is that you are actually inserting the lip of the boot into its groove prior to inserting the piston into the cylinder. Therefore you have some wiggle room to feed the lip in, starting at the bottom. I had a wooden popsicle stick on hand to help nudge it home where needed.

Take your time with this and it should work easily. The Sil-Glyde certainly helps it all go together and works much better than just brake fluid.

Now on to the guide bushings. The stock bushings are made of rubber, which is maintenance free and quiet. Unfortunately it also allows for some unnecessary movement in the caliper and will deteriorate over time like any other rubber part. This extra flex can lead to uneven pad wear, which was definitely visible on the EBC pads. Tapered pads can reduce pedal feel and stopping power, things you like to eliminate in a sports car, especially in a track environment. The alternative option is installing brass guide bushings, which eliminate the flex. The downside is that they require regular maintenance to insure they are properly lubricated to prevent sticking.

These brass bushings can be found at several vendors, most notably BimmerWorld. The install is pretty straight forward, with only a set of snap-ring (aka circlip) pliers as far as required special tools. The old guide bushings came out easily enough by hand, just pull them through by grabbing a hold of the long inboard end. A set of pliers can be used for extra motivation.

With the old bushings out, make sure you clean the now empty hole of any rust or debris. I also applied a thin coat of high-temp copper anti-seize to insure they wouldn’t become corroded and stuck in the caliper. The bushings are inserted from the rotor side of the caliper, so that the snap-ring groove is facing inboard.

On two of the front caliper bushings I had to do a small amount of clearancing, as there is a little variance in the casting which resulted in interference with the brass bushing sliding easily into the hole. A die-grinder made quick work of this, though a hand file would work just as well.

With the bushings installed in the caliper, next you must install the snap-rings from the backside. Now onto the caliper brackets and the guide posts. The BimmerWorld kit includes new posts, which look nearly identical to the stock posts, though I didn’t take a micrometer to them. I clamped the center of the bracket in a bench vise to remove the OE guides, which requires a 7mm Allen socket. The new ones go in and are torqued to 22 lb-ft.

You can see in the photo above that the guide posts received a light coat of copper anti-seize, as recommended by BimmerWorld. There is certainly plenty of debate on what type of lubricant to use, and I contemplated using some moly dry-film lubricant or ceramic brake lubricant. Since I see galvanic corrosion between the dissimilar metals being the main issue, the anti-seize is probably the best choice. A light coat was also applied to bore of the brass bushings. The fit tolerance is fairly tight, so the majority of the grease is going to be pushed out of initial assembly anyways.

NOTE: As mentioned, these brass bushings require regular checks. This isn’t much of a concern on a regularly track-driven car, because you are likely changing pads on a regular basis or at least checking the car prior to a track weekend. Since there is no rubber dust boot, the necessary grease will attract dust and other grime. Lack of lubricant or particulates lodged in the bushings can cause a caliper to stick, failing to properly retract and creating a dragging rotor. For these reasons, it is recommended that these bushings be used for track or race cars rather than a regularly driven street vehicle, though many folks do use them on their street cars. I intend to evaluate them during an upcoming track weekend. I plan to swap pads following this event and will check them at that time and swap back to new OE rubber bushings if need be. This is my daily-driver after all.

With work done on the calipers, now it’s time to put on the pads. As previously mentioned, I had a set of lightly used PFC 08 pads and BimmerWorld titanium backing plates which I will be using for this upcoming even. I’m fortunate that the M Coupe and M3 share their brake setups, allowing me to swap parts. I have run these pads and plates at NOLA and COTA, where I was very impressed with the performance. The 08 compounds did exhibit a small amount of pad fade at COTA towards the end of the session, but that’s not totally unexpected given the huge speed changes at the ends of two very long straights. I was very pleased with the titanium backing plates, which shield the dust boots and caliper from the majority of the brake generated heat. They came off the car scorched blue and purple, but the dust boots looked good as new. The only downside is that they require the removal of the metal clip that slides into the piston, which leads to a little rattle noise when driving slowly and off the brakes.

Now for the rotors; a set of lightly used Centric blanks. I had recently installed these on the M3, so rotor thickness was still very good, but the EBC pads had bedded and grooved them to a the point where I decided to have them turned smooth. A local shop made quick work of them and left them looking almost like new. Prior to installing the rotors, I applied a thin coat of the familiar copper anti-seize. This helps to prevent rust and galvanic corrosion, which can lead to a rotor becoming stuck to hub.

On goes the rotor and caliper. You may notice that I have a wheel bolt and two big nuts… okay, I have used two large nuts…. dangit, alright there are two large fastening devices and a wheel bolt used to secure the rotor to the hub. The nuts were used simply as spacers since the bolt by itself would bottom out on the dust shield. This was necessary due to the OE rotor bolt becoming seized into the hub, which required drilling out. Of course this is only a temporary measure used to aid in installation of the caliper.

With the lines reconnected, the air must be bled off. I topped off the reservoir using the same Brembo LCF 600 that I have been using, and hooked up my battered Motive pressure bleeder. I worked my way around the car as normal, bleeding off all the air from the empty lines and calipers. After that I gave the pedal a few pumps to push the pistons out until the pads made contact with the rotors, then rebled the system a second time.