2012-2018 BMW 335i Front vs Rear Brakes: What Wears First and What to Replace

By Core Brake Parts Tech Team — Circleville, OH warehouse

On a 2012-2018 BMW 335i the front brakes almost always wear out first, because the front axle carries more weight and does more of the stopping. The rears are not maintenance-free, though: BMW tracks each axle separately, each axle has its own pad wear sensor, and the rear pads on these cars can still come due before you expect them. Here is how the system is laid out on the 335i, how to tell which end needs work, and what to buy.

How the 335i Brake System Is Laid Out

The F-chassis 335i (and the 340i that followed it on the same platform) uses four-wheel disc brakes, but the exact hardware depends on how the car was optioned. That matters more than anything else when you order parts, because the standard brakes and the blue-caliper M Sport brake upgrade use different rotor sizes at both ends.

Two points catch people out. First, the M Sport appearance package (P337A) did not change the brakes on the 335i; those cars take the same 340 mm front and 330 mm rear rotors as a base car. Only the blue-caliper brake upgrade (S2NHA) moves to the 370 mm front and 345 mm rear discs. Second, the parts do not cross over: a 340 mm rotor will not fit a car with the blue calipers, and a 370 mm rotor will not fit a standard caliper. Look at your calipers before you order. Blue calipers mean the upgrade; grey calipers mean the standard setup.

Why the Fronts Wear First (and Why the Rears Still Matter)

When you brake, weight shifts forward onto the front tires. The front axle already carries more of the car's weight, and brake proportioning is set so the front brakes do most of the work. Hawk Performance sums it up plainly: the front carries more of the braking load, so front pads and rotors usually wear faster than the rears. The larger front rotors on the 335i exist for the same reason, to soak up and shed more heat.

The rears still wear, and on a BMW they are part of the stability system as well as the stopping system. Stability control and traction control apply individual brakes to keep the car straight, which puts wear on the rear pads even when you are not pressing the pedal hard. The practical result is that many owners replace front pads one or more times before the rears come due, but you should never assume the rears are fine without looking.

How BMW Tells You Which End Needs Brakes

The 335i does not guess at brake wear from a single sensor. It uses Condition Based Service (CBS), which keeps a separate remaining-life estimate for the front and rear brake pads and shows them in the service menu. Each axle has one pad wear sensor clipped into an inboard pad. On the rear, published F30 service procedures place it on the driver's side caliper.

BMW's own service bulletin SI B34 03 13, filed with NHTSA, explains how the two parts work together. The sensor itself triggers when pad thickness reaches about 4.2 mm. Between sensor trips, CBS runs a software wear model to forecast remaining life. On F30 and F31 cars produced from July 2011 through June 2013, that wear model could show a brake service warning while the pads still had more than 4.2 mm left. BMW's fix was a software update plus entering the measured pad thickness into the car.

What this means for you:

• A yellow brake service message on an early car is not proof the pads are gone. Pull the wheel and measure the pads before you buy anything.
• A red brake warning with a wear-sensor message means a sensor has actually tripped. The pad has reached the sensor, so plan the job now.
• Check both axles every time. CBS tracks front and rear separately, so a front warning tells you nothing about the rears.

Symptoms: Front vs Rear

A note on "warped rotors": Hawk points out that rotors rarely truly warp. The shake you feel usually comes from pad material deposited unevenly on the rotor face, which creates high spots. Severe steering shake that does not change with braking effort is more often a suspension or tire problem than a brake problem.

What to Replace, and What to Replace With It

Front brake job. Replace pads on both sides of the axle, the front wear sensor, and in most cases both front rotors. On the standard car those are the 340 mm two-piece rotors. On blue-caliper cars they are the 370 mm discs. If the rotors are grooved, have a lip, or measure at or below the minimum thickness cast into them, replace them rather than trying to reuse them. For a matched set, the Brembo OE front disc brake kit KT04472 with low-met pads and drilled and slotted rotors for the 2012-2018 335i and 340i puts pads and rotors in one box. Confirm the rotor diameter against your car before ordering.

Rear brake job. Replace pads on both sides of the axle, the rear wear sensor, and the rear rotors if they are worn or scored (330 mm standard, 345 mm with the blue M Sport brakes). The rear rotor is held to the hub by a small set screw that takes a 6 mm hex bit. Seat the bit fully so you do not strip it. Browse replacement brake rotors and front and rear brake pads by position.

Always replace the wear sensor. BMW sensors are single-use once the tip has worn into the rotor. Even an untripped sensor often gets brittle and breaks when you pull it out of the old pad. A new sensor is cheap insurance against a false warning the week after the job. After the job, reset the brake service item for the axle you serviced so CBS starts a fresh forecast.

Hardware and fluid. Replace clips and guide-pin boots that are torn or corroded; see brake hardware kits. BMW services brake fluid on a time schedule tracked by CBS, separate from pad wear. If the fluid service is due or close, doing it with the pads saves a second trip.

How Hard Is the Job?

Both ends are a reasonable driveway job for someone who has done brakes before. Front pads and rotors are the more straightforward of the two. On the rear, the caliper piston is pushed back with an ordinary caliper piston tool. That is different from many newer BMWs, whose electric parking brake calipers have to be retracted with a scan tool. Before you compress any piston, check the fluid level in the reservoir, since pushing pistons back raises it.

Torque every fastener, from the caliper carrier bolts to the guide pins and wheel bolts, to the values in the factory service information for your exact car. Some BMW carrier bolts use a torque-plus-angle procedure, so do not guess. Bed in new pads and rotors with a series of moderate stops from speed, so an even pad layer forms on the rotors. That even layer is what prevents the uneven deposits that cause vibration later.

Frequently Asked Questions

Do I need to replace front and rear brakes on my 335i at the same time?

No. Each axle is serviced on its own schedule, and the fronts usually come due first. Always replace pads in pairs on the same axle, and check the other axle's pads while the car is in the air.

How do I know if my 335i has M Sport brakes?

Look at the calipers. The blue-caliper M Sport brake upgrade uses 370 mm front and 345 mm rear rotors. Grey calipers mean the standard 340 mm front and 330 mm rear setup, including cars with the M Sport appearance package.

My car shows a brake service warning but the pads look fine. Why?

CBS forecasts wear with software between sensor trips. On F30 cars built from July 2011 through June 2013, BMW service bulletin SI B34 03 13 covers a wear-model error that could warn early. Measure the pads. If they are well above the roughly 4.2 mm sensor point, a dealer software update and pad-thickness entry clears it.

Do I have to replace the brake pad wear sensor?

Yes, if it has tripped, because the worn tip cannot be reused. Most technicians replace it with every pad job anyway, because old sensors get brittle and break on removal.

Can I put 370 mm rotors on a car with the standard brakes?

Not by themselves. The rotor size is tied to the caliper and carrier, so the larger rotors only fit with the matching M Sport brake hardware.

Sources

1. BMW Service Information SI B34 03 13 (via NHTSA) - CBS tracks front and rear pad life separately; pad sensor intervenes at 4.2 mm; early-production F30/F31 wear-model warning and fix
2. BimmerWorld - Genuine BMW 340 x 30 mm front rotor - standard 335i/340i front rotor size, two-piece construction, fitment by package
3. BimmerWorld - BMW 330 x 20 mm rear rotor - standard 335i/340i rear rotor size; not for the blue M Sport brake upgrade
4. BimmerWorld - 370 x 30 mm front rotor (S2NHA) - M Sport brake upgrade front rotor size
5. BimmerWorld - 345 mm rear rotor (S2NHA) - M Sport brake upgrade rear rotor size
6. Hawk Performance - When should you replace brake rotors - front axle carries more braking load and wears faster; rotors rarely truly warp; minimum thickness guidance
7. FCP Euro - How to replace BMW F30 rear brake pads and rotors - rear wear sensor on the driver's side inboard pad; rear piston compresses with a piston tool; 6 mm hex rotor set screw