2017-2023 Mercedes-Benz E350 Front vs Rear Brakes: What Wears First and What to Replace

By Core Brake Parts Tech Team — Circleville, OH warehouse

On a 2017-2023 Mercedes-Benz E350, the front brakes almost always wear out first, because weight shifts forward every time you stop and the front axle does most of the work. The rears last longer, but they are not a simple job: they carry the electric parking brake, so the calipers have to be put into service mode before the pistons can be pushed back. Plan on replacing pads and rotors as an axle set, with a new wear sensor each time.

How the Braking Load Splits on the E350

Every car is built so the front brakes carry more of the stopping load than the rears. When you brake, the nose dives and weight moves onto the front tires, so the front pads and rotors have more grip to work with and more heat to absorb. Manufacturers size the front brakes bigger to handle that. One general automotive reference puts the rear share at 40 percent or less of total stopping power on a typical car.

The bias is deliberate. If the rear brakes were stronger than the fronts, the rear tires could lock first in a hard stop and the car could skid or spin. So on the E350, as on nearly every sedan, expect to replace front pads more often than rear pads. It is normal to go through more than one set of fronts before the rears need attention, though the exact ratio depends on how and where you drive. Heavy stop-and-go city driving, hilly roads and frequent highway exits all shift the numbers.

The E-Class also uses electronic stability and anti-lock systems that can apply individual brakes, which is why you should never assume the rears are fine just because the fronts were recently done. Measure both axles at every tire rotation.

The Two Warning Systems: Sensors and Your Eyes

Mercedes-Benz uses electronic pad wear sensors rather than squealer tabs. Typically there is one sensor per axle: one at the front left wheel and one at the right rear wheel. When the pad material wears down to its minimum thickness, the sensor contacts the rotor and the instrument cluster shows a check brake pad wear message.

Two things to know about that message:

• It is a last call, not an early warning. Once it appears, you are typically looking at a few hundred miles of pad life, not thousands. Book the job right away.
• The sensor is single use. Once the pad wears into it, the insulation is damaged and the wire is exposed, so it cannot be reused. Always install a new sensor with new pads on the axle that has one.

Because there is only one sensor per axle, it only reports on that one wheel. A sticking caliper slide or a seized piston on the opposite side can wear the other pads faster, and the dash will never tell you. That is the reason to pull the wheels and look at all four corners, both inner and outer pads, whenever you service the brakes.

Symptoms by Axle

Front Brake Job: What to Replace

The front job on the E350 is a conventional pad and rotor replacement. On the front axle, replace these together:

• Pads for both front wheels. Low-dust ceramic compounds suit most daily-driven E-Class sedans; browse our ceramic brake pads.
• Rotors for both sides. Mercedes rotors are commonly replaced with every pad change rather than resurfaced, and if they are below the minimum thickness cast into them or show heavy grooving or a lip, they have to go. See our brake rotors.
• A new wear sensor if the front left position has one.
• Hardware: clean the bracket and hub faces of rust and debris, and apply brake grease to the pad contact points, the pad backs and the guide pins. Fresh clips from our brake hardware kits help keep the pads quiet.

The rotor on many Mercedes models is held to the hub by a small retaining screw (a T30 on the models covered by one dealer service guide), and the caliper bracket bolts have to come out to remove the rotor. Torque every fastener to the value in the factory service manual; do not guess.

Rear Brake Job: The Electric Parking Brake Step

Most 2015 and newer Mercedes-Benz models, the E-Class included, use an electric parking brake built into the rear calipers. The motor is mechanically linked to the piston, so you cannot just lever the piston back like on an older car. Doing that can damage the motor or caliper mechanism and set a fault.

Instead, the rear calipers must be moved to the fitting position first. On the W213-generation E-Class, one published procedure is: with the cluster off, press the start button once, then press and hold the parking brake button while the cluster comes on; a brake pad replacement mode appears on the display; select the option to move to the fitting position and wait until the pistons fully retract. Another route on many Mercedes models is a hidden service menu reached through the steering wheel buttons. If neither works on your car, a scan tool with an electric parking brake service function will retract the pistons.

With the pistons retracted, open the brake fluid reservoir cap so fluid can move back as the pistons are pushed in, then unplug the rear wear sensor and replace the pads, rotors and sensor. After reassembly, exit service mode so the parking brake reapplies, and pump the pedal several times before moving the car. For the back axle we carry the Power Stop rear ceramic brake pads for the 2017-2023 E350; you can also browse the full Power Stop range.

Fluid, Calipers and How Hard the Job Is

Brake fluid absorbs moisture over time, which lowers its boiling point and lets corrosion start inside the calipers and ABS unit. Mercedes-Benz includes brake fluid exchanges in the scheduled E-Class maintenance, so check your maintenance booklet or the service display for when it is due, and use the fluid spec printed on the reservoir cap or in the owner's manual. If the fluid is due, doing it with a pad job saves a second visit.

Inspect the calipers while the wheels are off. A torn piston boot, a weeping piston or slides that will not move freely mean the caliper should be rebuilt or replaced, or the new pads will wear unevenly. Replacement units are in our brake calipers collection.

Difficulty: the front job is moderate for a home mechanic with a torque wrench and jack stands. The rear job is the same work plus the electric parking brake step, so it is only as easy as getting the calipers into service mode. If you are not comfortable with that, have a qualified shop do the rears.

Frequently Asked Questions

Do the front brakes on an E350 always wear out before the rears?

In normal driving, yes. The front axle does most of the stopping because weight transfers forward under braking. Still measure the rears at every service, since a sticking caliper or heavy city use can wear them faster than expected.

Do I have to replace the wear sensor every time I change pads?

Replace it whenever the old pad has worn into it, which is the case any time the dash message came on. The sensor is single use once its insulation is worn through. Many owners replace it with every pad change on that axle so the warning stays reliable.

Can I change the rear pads without a scan tool?

Often, yes. The W213 E-Class has a procedure using the start button, the parking brake button and the cluster display to move the calipers to the fitting position. If that menu does not appear on your car, a scan tool with an electric parking brake service function does the same job.

Should I replace the rotors with the pads?

On an E-Class, rotors are commonly replaced with the pads. If they are under the minimum thickness marked on them, grooved or causing vibration, new rotors are required. Fresh pads on worn rotors bed in poorly and can bring back noise and vibration.

How long do I have after the brake pad wear warning appears?

Typically a few hundred miles. Treat the message as a sign to book the job now, not at the next oil change.

Sources

1. SlashGear - Why front brake pads wear out faster - weight transfer, rear share of 40 percent or less, reason for front bias
2. YOUCANIC - Mercedes-Benz check brake pad wear message - sensor locations, single-use sensors, remaining life after the warning
3. YOUCANIC - Releasing Mercedes-Benz electric parking brakes - 2015 and newer E-Class uses an electric parking brake; service menu and scan tool methods
4. ScegliAuto - W213 E-Class rear brake pad service mode - W213 fitting-position procedure and opening the reservoir cap
5. Mercedes-Benz of Huntington - How to change Mercedes-Benz brake pads - sensor replacement, T30 rotor screw, bracket bolts, greasing and cleaning