My M Roadster's braking system needed a refresh, but instead of just replacing the pads, I decided to completely overhaul the calipers, install new rotors and pads and then flush the system.
The M Roadster's stock braking system is more than ample for the car, but my car was fitted with stainless steel brake lines which reduce the sponginess of the stock rubber lines and help give the system a little more bite. The previous owner had also upgraded to cross drilled rotors, similar to the ones used in the next generation Z4 M Roadsters. I decided I like the look and potential performance advantages, so I ordered new cross drilled rotors front and back. As for pads, I went with stock replacements, but I could have easily upgraded to more performance oriented pads. For my everyday driving purposes, the stock pads will provide more than enough stopping power.
Rebuilding the Front and Rear Brake Calipers
Parts: (2) Ate front BMW caliper repair kit, 34-11-1-157-037-M4 ($24),
(2) Ate rear BMW caliper repair kit ($24)
(2) Ate SL Brake Fluid ($35)
High temperature brake caliper paint (Black) ($7)
Brake pads, front and rear ($150)
Labor: 8 hours+, including cleaning and painting ($1,040)
Special tools: Air pump, mallet & seal driver or other tool to press the piston & seal back into caliper
The passenger side front brake caliper was making a metallic snapping sound anytime the brake pedal was pressed. Initially I thought the brake line bracket or brake pads were loose, but after removing the brake caliper, inspecting the parts and reinstalling them the noise persisted. It was evident that the caliper O-ring and seal needed to be replaced. The seal or O-ring can become damaged or simply wear out due to dry and excessively hot temperatures. It's not uncommon for older cars to need their brake calipers rebuilt.
The rebuilding process is fairly straight forward but can be time consuming for first timers, especially the reassembly of installing the piston and seal back into the caliper. For that reason it might make more sense to just buy new calipers, as they are readily available.
In essence the process requires removing the caliper from the car but unbolting it from its bracket and unscrewing the brake line. Brake fluid will leak out, so be prepared by having a reservoir for the fluid. Then air is applied to the brake line hole of the caliper to push the brake piston out. This can be a dangerous process and requires placing a spacer between the piston and the inside of the caliper to capture the piston as it flies out. Once removed the O-ring inside the piston and the seal around the top of the caliper opening are replaced. The piston needs to be inspected and cleaned before reinstallation. The reinstallation process requires even pressure on the piston as it seats tightly back into the caliper. I used a mallet and a seal driver that fit the diameter of the piston to slowly drive it back in. Once this is done, the caliper is properly reinstalled on the car, followed by the brake line, and then the brake system will need to be bled.
Since the calipers are off the car, this would be an ideal time to bring them back to life by degreasing them and repainting them with high temperature brake caliper paint. This job can take roughly 1-2 hours since the calipers are already off the car and the finished product will help make the brake system look new again.
When new, the M Roadster's brake calipers were painted a semi-glossy black. Over time, due to brake dust, heat and the elements, the black finish can fade. To fix this issue properly the calipers need to be removed from the vehicle, thoroughly cleaned of brake dust and grime, and then painted with two or more coats of black high temperature brake caliper paint. The mounting brackets which the caliper connects to should also be removed, cleaned and painted. I also had the metal clip for the brake pads painted silver so the brakes would have their OEM look again. If you’re not replacing your rotors, this would also be a good time to clean and paint the center of the rotors to match the calipers. Although you can paint your calipers any number of colors, if the goal is to make the car look like new again, the brake calipers shouldn’t be too shiny or painted any color other than black.
Once everything is back together, it's time for a thorough brake fluid flush. I start by removing old fluid from the reservoir and use my power bleeder to flush the system. Although this isn't always necessary, I also flushed the clutch slave cylinder as the fluid was very old and I wanted every drop out of the system.
Replace Brake Rotors
Parts: (2) StopTech front cross-drilled disk rotors ($200),
(2) StopTech rear cross-drilled disk rotors ($150)
Labor: 4 hours or $520 (estimated)
Special tools: Girodisc brake caliper press or similar tool (not necessary, but preferred)
During the time I had test driven the M Roadster, I noticed a little vibration in the brake pedal under hard breaking. My hunch was that the front rotors were a little warped and needed to be replaced. Since the rear rotors had a good deal of wear, I decided to replace all of them at the same time. For the replacement rotors I decided to go with Stoptech cross drilled, front and rear. There are so many choices for brands and styles. I chose the cross drilled rotors because they’ll help fend off brake fade during continuous heavy braking and Stoptech is a brand I can trust. The installation is fairly straight forward and requires some post install driving and braking to bed-in the pads to the new rotors. After pudding hundreds of miles on the new rotors, the only downside I found was a little less initial bite in heavy rain when the rotors are wet. This would not as much of an issue with stock rotors, since there is more surface area. Where these rotors shine is under situations of hard and continuous braking.