Let's replace a set of brakes

[Flexray]

I dislike doing brakes. Brake dust is terrible, you always somehow end up having blackface when it's all over.

Let's do a $1000 brake job on a BMW. I'm not going to do some super cheap Amazon pad slap. This is a BMW, the ultimate driving machine, it will be treated as such.

2008 335i E93 81000km. I get assigned a work order that states to replace the front brakes. I get in the car and see this message displayed. The pad sensor is touching the brake rotor, or there is a problem with the sensor.



I put the vehicle on the lift and remove both front wheels. I inspect the brakes. The inside pads have 2mm and the pad sensor is touching the rotor, the outside ones have 4mm. BMW spec says there should be less than 1mm difference in between the inside and outside pads. This technically is a problem, but I'm not going to get too worked up about it. If it was 2mm inside and 6mm outside, then we would take a different path.





I'm assuming that the brakes are being replaced because they are worn out and not noisy or pulsating. Diagnosing noises and pulsations is a topic on its own. The left front brake has a pad sensor, the right side does not. I unplug the pad sensor from the vehicle side connector, I unclip the sensor off of it's mounting points on the suspension strut and leave the sensor still connected to the inboard brake pad. I unscrew the caliper mounting slide pins that attach the caliper to the bracket. I tuck the caliper in-between the tie rod end/control arm/ and strut. Brake calipers should never be left hanging from their hoses. Hoses are not designed to hold weight. It is best to hang them by a bungee cord.



I remove the two mounting bolts for the brake caliper bracket and remove the bracket. I remove the brake rotor mounting screw. I give the rotor a light tap with a hammer while holding it so it doesn't fall.

[Flexray]

This is the worst part. But one of the most important. Time to clean. I'm going to use a 3" wire wheel in a die grinder and another die grinder with a rotary Scotch Brite disk. I use both of these on the wheel hub. The surface that the rotor sits on must be free from all corrosion. If the rotor is not perfectly flat on the wheel hub, it will have excessive run-out. This will cause a brake pulsation over time.





I spray off the caliper bracket with brake clean to remove some of the brake dust. The pad channels have to be cleaned and lubed. This is what actually holds the pads in place. These channels let the pads move as they wear. If there is corrosion or dirt build up in these, the pads can corrode in place. Causing uneven pad wear. I hit them with the 3" wire wheel. This removes all of the loose stuff, but there is a layer of hard corrosion. I use a square file to remove this. I want to see bare metal, but don't want to remove too much metal. If I do, the pads will be able to move around too much and can causing a clicking type noise. Using a silicone lubricant, I put a thin layer in all of the pad channels. A pea sized blob is more than enough to do one bracket. This lube is meant to reduce squealing. Too much lube, and it will collect dirt and also start squealing. That tube of lube will do a few hundred brake jobs.



Using a pad pusher, I push the caliper pistons back into the caliper. I give the caliper a spray with brake clean. Using a Scotch Brite pad, I clean the piston face where it contacts the pad. On the other side of the caliper, I clean where the outboard pad contacts the caliper. I give these surfaces a thin coat of lube.

[Flexray]

I push the caliper slide pins out of the caliper. They have a bunch of rubber and corrosion stuck to them. I give them a clean with a wire wheel on a pedestal grinder. I put a heavy coat of lube on them and push them back into the caliper. If these pins seize. It will cause inboard/outboard uneven pad wear. Or wedge type pad wear.



I'm about to put on new parts. Brakes are a friction set. The pads and rotors wear into each other. The old rotors measure above discard spec, but they are getting replaced. Think of a used rotors as a vinyl record. The pads wear grooves into it, and deposit pad material onto it. If you install new pads onto a used rotors. The pads have to conform to an already worn rotor. Usually resulting in poor braking and sometimes a pulsation. New pads and rotors will wear together naturally and have the proper friction coefficient. I'm installing Zimmermann rotors with Textar pads. These are good quality aftermarket replacement parts, you get what you pay for. I install the rotors onto the wheel hub. I put the caliper bracket on and torque the mounting bolts. I install the brake pads into the caliper bracket. I install the caliper over the pads and torque the mounting slide pins. I click a new brake pad sensor into the inboard pad, route the plug to the vehicle side connector and plug it in.





The pistons in the calipers are fully pushed in. I pump the brake pedal a few times until the pistons make contact with the pads and I get a good solid brake pedal. I check the brake fluid level in the reservoir, it is just below the full mark, right were it should be. We now have to tell the vehicle that we replaced the front brakes. Using a scan tool, I check the condition based service data.



These are all calculated values, based off of time and milage. When I reset the front brakes. The vehicle learns the new brake pad sensor resistance, logs a brake replacement, and resets the percentage to 100%.



As I'm backing out of my bay, I stop a few times. I want to make sure I can actually stop before I start driving through the shop and out on the street. I have had a lot of fun experiences breaking in brakes on public roads. I will accelerate to about 50km/h, with light brake pressure, slow down to like 10. Speed back up to 50, then brake down to 10 with moderate brake pressure. I do this about 10 to 20 times. I get onto a bigger road, get up to about 80, moderate to hard braking down to 60-10 depending on traffic. About 10 to 20 times. Non-coated rotors that have been covered with packing oil will smoke like a bastard at this point. You attract a lot of attention at red lights. Through this process, you will feel the brakes seat in and start grabbing harder and harder. Its usually about a 20 minute test drive, but It takes about 500km for them to fully break in.

This process is basically how all automotive disk brakes are replaced. You would replace the brakes on a F-350 the same way.

I was in no big hurry doing this job. From getting the keys to parking it back in the parking lot, I spent 2 hours.

[ThePenIsMightier]

You mentioned smoking rotors if they come coated with a lube. I would always rinse that crap off with BrakeClean prior to bedding. Isn't that recommended rather than baking it off?

[Flexray]

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You mentioned smoking rotors if they come coated with a lube. I would always rinse that crap off with BrakeClean prior to bedding. Isn't that recommended rather than baking it off?

You wash as much of the oil off as you can with brake clean. The oil will destroy the pads. But oil gets trapped in the vents of the rotor, that is what smokes.

[ThePenIsMightier]

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You wash as much of the oil off as you can with brake clean. The oil will destroy the pads. But oil gets trapped in the vents of the rotor, that is what smokes.

Thank God. I thought you were talking about just leaving that stuff on. LoL!!

[BerserkerCatSplat]

I had assumed for the longest time that the electrical brake wear sensors were a relatively recent thing and then I saw VGG's video that had them on an early 70s Pantera. Guess they've been around for a while.

[g-m]

Interesting, I've done my fair share of brakes but I've never wire wheeled the hub or pistons. I'll definitely add that to my list thanks!

Also I hate sliding pin brakes and I'm surprised that's on a 335. I would've expected fixed calipers

[mr2mike]

Just don't knick the caliper piston boot and rip it.

[Flexray]

The piston face and caliper get cleaned by hand with a Scotch Brite pad. No power tools.

[nismodrifter]

Thanks for keeping these posts coming. Always lots of great info.