E30 M3 Rebuild: Brakes
A BMW E30 M3 has taken up residence in our shop this winter—in out of the cold Midwest winter for a deliberate going over. The car has been tracked extensively and things have begun to wear out. We have been tasked to do a thorough technical inspection, replace, rebuild or repair what’s bad and give recommendations where the aftermarket has made improvements over the original equipment hardware. In other words, make it just I bit better than new.
The owner has no complaints with the stopping power of the OEM brake system, so what we have decided to do is rebuild the main components and replace a few smaller items with better bits.
Inspecting the brake we immediately noticed that the rubber piston dust boots need to be replaced. BMW offers rebuild kits that include all the necessary boots and piston seals. Turner Motorsports offers an upgrade kit that replaces the plastic caliper guide bushings with brass ones. They contend that the brass bushings “will eliminate caliper twisting caused by rubber guide pin bushings” and “will allow (the) calipers to squeeze evenly on both sides of the brake rotor just like multi-piston big brake kits” resulting in longer pad life and more consistent brake feel.
The first thing we like to do is clean up the work area and/or parts. This particular car is pretty filthy thanks to its age and dirt roads its driven on.
To rebuild the calipers it's best to take the complete brake system off the car. Here are the parts off the car:
As you can see, the parts were still very dirty, caked with brake dust and road grim. Surface rust also covered the calipers. to clean them up we sent the parts out the shot blaster before we took the pistons out. This way the critical mating surfaces-- the cylinder walls and piston surface would not be damaged.
To remove the piston we first peeled off the dust boots and then pressurized the caliper cylinder with compressed air to gently push it out. This picture shows how much sludge was built up on the inside of the cylinder:
Here are the disassembled brakes all cleaned and ready to be painted:
We sprayed several coats of premium high heat black caliper paint onto the exterior surfaces of the parts taking special care not to get any paint into the cylinder, bleeder or brake line hole. Here we see all the parts ready to assemble:
First the piston seal was installed in the cylinder, a staright forward procedure. To get the boots back on is a little tougher. We have found it best to first put the boot over the end of the cylinder, then insert the boot end into the cylinder groove.
We next install the piston slowly into the cylinder and just before it's all the way in, seat the boot in the piston groove. It should all snap into place once the piston is all the way in. To help ease the piston in and seal the boots we used ATE brake caliper grease.
Finally we installed the brass bushings from Turner Motorsports:
The brakes are now ready to install back onto the car. We will also install new stainless steel brake lines to finish the brake rebuild/upgrade.
A thorough job takes time and attention to detail. The stock brakes on the E30 M3 are plenty strong even on the track. With these few upgrades to the calipers they should work even better.