Recently I heard my front brakes squealing and knew it was time to replace them. Brake pads are designed to make noise like this when nearing the end of their lifetime to give an audible cue that they need to be replaced soon. Foregoing this maintainance item will completely wear away the brake pad material resulting in metal-on-metal contact between the rotor surface and the metal plate on which the brake pad is mounted.
The brakes on my car are simple disc brakes. Pressing the brake pedal in the cabin will compress a set of brake pads mounted in the wheel well against a rotor which is coupled to the tire. The wheel is slowed as the brake pad material grips the rotor and the kinetic energy of the wheel is dissipated as heat, slowly wearing down the brake pad over its lifetime until it becomes thin and needs replacing. The brake pad material is ejected as brake dust and is one of the dirtiest things a car ejects regularly, ignoring its exhaust fumes. It's impossible to even look at brakes without getting dirty.
Featured prominently in the above photograph is the rotor which is the shiny metal surface. Behind that is the brake caliper which holds two brake pads near the rotor. Brake fluid compresses a piston according to Pascal's Law which pushes one pad against the rotor while the opposite pad remains stationary, squeezing the rotor during braking. Lug bolts couple the wheel to the hub which itself is coupled to the rotor. Many cars use lug nuts and studs to secure the wheel to the hub but for some reason BMW uses lug bolts which are more hassle to mount and unmount. Rotors need to be replaced sometimes too when they wear below their recommended thickness.
Brakes in the front of cars are bigger than the brake pads in the rear because weight is transferred to the nose of the car during hard braking, when the nose of the car dives. The front brakes do more work to stop the vehicle in this state than the rear brakes.
Changing Brake Pads on an E36
Tools needed
- 17mm socket and socket wrench
- 7mm allen key
- Breaker bar
- Pliers
- Flathead screwdriver
- Brake grease
- Micrometer
- Small piece of wood or a tool to compress the brake piston
Procedure
- Crack the wheel lugbolts loose with the breaker bar while the vehicle is on the ground, otherwise the wheels will spin while in the air as you try to break the bolts loose
- Lift the vehicle with a jack and stands
- Remove all lugbolts and pop off the tire. May need some coercion if it has been a while since the wheel was removed
- Inspect the pads and measure the rotor thickness with a micrometer
- Remove the two plastic caps covering the caliper guide bolts by shimmying them out with the flathead
- Remove the guide bolts with the 7mm allen key
- Remove the brake pad sensor wire if present
- Pry off the brake pad clip (watch your eyes) and hold on to the caliper to make sure it does not fall off the rotor
- Remove the caliper, may require some coercion with a mallet or flathead. Don't scratch the rotors!
- Remove the old brake pads from the caliper
- Press the piston back with a piece of wood or the special tool to make room for the new, thicker pads
- Press the new brake pad into the compressed piston and straddle the rotor with the other new pad
- Reinstall the brake pad clip
- Grease the guidebolts and reinstall, ensuring they thread correctly
- Replace plastic caps and remount the wheel to the hub, tighten, lower the car and torque to spec (88 ft lbs for my car)
It's not clear to me how old these old Textar brakes were but they have a BMW logo so they must have been installed by BMW itself, as my new brakes are from the same OEM supplier (Textar) but lack the logo.
Just to be complete I also replaced the rear brake pads and cleaned up the brake dust that coated the wheel well and everything in it. All together it was probably 6 hours of work for me over two days and at the end of this work it looked like I crawled out of a coal mine. I showered and scrubbed the dust off my face and body vigorously.