2006-2018 BMW 335i Brake Caliper Problems and Replacement

By Core Brake Parts Tech Team — Circleville, OH warehouse

Most BMW 335i caliper problems come down to three things: a sliding caliper whose guide pins have stopped sliding, a piston that has corroded behind a torn dust boot, or a seal that has started to weep fluid. The signs are a pull to one side, one wheel far hotter than the others, a burning smell, or pads worn much thinner on one side. The fix is usually a replacement caliper (or a rebuild) plus fresh pads and a fluid bleed, and on the 335i it is a job a careful home mechanic can do in an afternoon.

What Calipers the 335i Uses

The 335i spans two generations, and the brake hardware is different between them, so identify your car before buying anything.

Two practical points come out of that table. First, on an F30 you have to know whether the car has the standard sliding calipers or the M Sport fixed calipers, because the calipers, pads and rotors are not interchangeable between the two. The M Sport caliper has pistons on both sides of the rotor and a one-piece fixed body; the standard caliper has its piston on the inboard side only and slides on guide pins. Second, neither generation of 335i uses an electronic parking brake in the rear caliper. The parking brake is a small drum-style shoe set that works on the inside of the rear rotor hat, so the rear caliper piston simply pushes back with a compressor tool; there is no motor to wind back and no scan-tool service mode for the parking brake on these cars.

Symptoms of a Bad 335i Caliper

A failing caliper usually announces itself in one of these ways:

• Pull to one side. The car drifts or pulls under braking, or even while cruising, because one caliper is dragging or not clamping evenly.
• One hot wheel and a burning smell. After a drive, one wheel is noticeably hotter than the others, sometimes with a sharp smell of overheated friction material. That wheel's pads are staying in contact with the rotor.
• Feels like the parking brake is on. The car coasts poorly and feels sluggish when you accelerate.
• Uneven pad wear. The inner pad on a sliding caliper is much thinner than the outer pad, or one side of the car wears pads far faster than the other. On a 335i this often shows up as an early brake pad warning on one axle.
• Fluid on the inside of the wheel or a dropping reservoir. A wet, oily film on the caliper body, the inside of the wheel or the tire sidewall points to a leaking piston seal or bleeder.
• Soft or long pedal combined with any of the above, which can mean air or fluid loss at the caliper.

To confirm, lift the car and spin each wheel by hand with the transmission in neutral. A healthy corner turns with light drag; a seized one fights you or stops almost immediately. Then pull the wheel and look at the pads, the piston boot and the guide pin boots.

Why 335i Calipers Stick, Seize or Leak

Brake caliper failures follow the same pattern on almost every car, and the BMW is no exception:

• Seized guide pins. The sliding caliper floats on guide pins sealed by rubber boots. When a boot tears, water and road salt get in, the pin corrodes and the caliper can no longer center itself. The inner pad then drags and wears out first. Using the wrong grease, particularly petroleum-based grease that swells rubber, can cause the same binding.
• Corroded piston. A torn piston dust boot lets moisture reach the piston. Rust builds up and the piston sticks in the applied position, holding the pad against the rotor.
• Worn or aged square-cut seal. The seal around the piston both seals the fluid and pulls the piston back slightly when you release the pedal. As it ages it can leak or stop retracting the piston.
• Old, wet brake fluid. Brake fluid absorbs water over time, and that moisture corrodes the caliper bore and piston from the inside. Brake manufacturer NRS recommends a fluid flush every two years for this reason.
• Loose or damaged bleeder. A bleeder screw with damaged threads or a bad seat will weep fluid.

Heat from hard use speeds all of this up. A 335i driven hard on a twisty road or at a track day puts far more heat through the calipers and fluid than a gentle commuter car, which is one reason owners of these cars change fluid more often.

Rebuild or Replace the Caliper?

If only the guide pins are stuck, you may not need a caliper at all. Clean the bores, fit new guide pins and boots, lubricate with the correct brake grease, and the caliper will float freely again. We cover that step in our guide to lubricating caliper slide pins.

If the piston is seized or the seal is leaking, you have two choices:

• Rebuild: Remove the piston, clean and inspect the bore, and install a new piston, seal and dust boot. Rebuild kits with pistons are made for these calipers. It costs less in parts but only works if the bore is not pitted, and it takes patience and clean working conditions.
• Replace: Install a new or remanufactured caliper. This is faster and removes the guesswork about bore condition. Browse replacement brake calipers and check the listing against your chassis and whether the car has standard or M Sport brakes.

Replace calipers in axle pairs when one has failed from corrosion or age. The other side has lived the same life, and a new caliper on one side with a tired one on the other can leave the brakes pulling slightly.

What to Replace at the Same Time

A dragging caliper almost always damages the parts around it, so plan to replace:

• Brake pads. Pads that have been dragging are glazed or worn unevenly. Fit a fresh set on both sides of the axle. For drivers who push the car, we carry EBC Bluestuff NDX pads for the 2006-2012 335i front (E90/E92/E93), the 2006-2012 335i rear, and the 2013-2018 335i F30 rear. EBC rates Bluestuff NDX as a fast-street and track-day pad with a high friction level, and asks for a gentle bed-in of about 200 miles on the street. For a quieter daily-driver pad, see our ceramic brake pads.
• Rotors. A seized caliper overheats the rotor, which can leave blue spots, hard spots or uneven deposits that cause vibration. If the rotor is below minimum thickness or heat-damaged, replace it. See brake rotors.
• Pad wear sensor. BMW pad wear sensors are one-time use once the pads have worn into them. Fit a new sensor with new pads on the axle that has one.
• Guide pins, boots and clips. A brake hardware kit is cheap insurance on any caliper job.
• Brake hose and fluid. Inspect the flexible hose for cracks or swelling while it is disconnected, and bleed or flush the system with fresh fluid of the type printed on the reservoir cap. Cracked hoses are covered in our brake hoses collection.

How Hard Is the Job?

For someone who has done a pad and rotor job before, replacing a 335i caliper is a moderate DIY job. Per corner you remove the wheel, disconnect the pad wear sensor if that corner has one, remove the caliper from its bracket, disconnect the brake hose at the caliper, fit the new caliper with new sealing washers on the hose fitting, reinstall pads and caliper, and bleed that corner.

Things that catch 335i owners out:

• Wheel bolts, not nuts. BMW uses lug bolts. A wheel-hanging pin makes refitting the wheel much easier.
• Torque procedures. Some BMW caliper bracket bolts use a torque-plus-angle procedure rather than a single torque value. Follow the torque values and sequence in the factory service manual for your exact car rather than a generic chart.
• M Sport pads. On M Sport fixed calipers the pads are held by pins and an anti-rattle clip, and the caliper needs a compressor that can push several pistons back at once.
• Bleeding. Minimize fluid loss by clamping the hose with a proper hose clamp tool while it is off, keep the reservoir topped up, and bleed until the fluid runs clear with no air. A pressure bleeder makes this far easier than the two-person pedal method.
• Pedal before driving. Pump the pedal until it is firm before the car moves. After pushing pistons back, the first press goes almost to the floor.

If the bleeder screw is seized or the hose fitting is rounded, stop and get the right tools or have a shop take over; a stripped fitting turns a caliper job into a hard-line repair.

Frequently Asked Questions

Can I drive my 335i with a sticking caliper?

Only as far as a safe place to repair it. A dragging caliper overheats the pads, rotor and fluid, which can lead to brake fade, and a seized piston can cause a strong pull under braking. It also wears pads and rotors quickly.

Do I need to replace both calipers?

If one failed from corrosion or age, replacing both on the same axle is the better choice so the brakes clamp evenly side to side. If one was damaged by something specific, such as a stripped bleeder, a single caliper is acceptable.

Does the 335i have an electronic parking brake I need to retract?

No. Both the E90-generation and F30-generation 335i use a hand lever and parking brake shoes inside the rear rotor hat. The rear caliper piston is pushed back with a normal compressor tool.

Can I fit M Sport calipers to a standard F30 335i?

The M Sport brakes use different calipers, brackets, rotors and pads, so it is a full brake package swap rather than a caliper swap. Standard-brake pads and rotors will not fit M Sport calipers, and the reverse is also true.

Why is only my inner brake pad worn out?

On a sliding caliper, a thin inner pad with a healthy outer pad almost always means the guide pins are binding or the piston is not retracting. Fix the pins or caliper, or the new pads will wear the same way.

What brake fluid does the 335i use?

Use the fluid specification printed on the reservoir cap and in your owner's manual. Do not add DOT 5 silicone fluid, which does not mix with the glycol-based fluid these systems use.

Sources

1. FCP Euro - BMW F30 M Sport front brake replacement - M Sport front calipers are fixed aluminum Brembo units with four pistons versus one on standard sliding calipers; pads held by pins and an anti-rattle clip
2. FCP Euro - BMW F30 M Sport rear brake replacement - two-piston fixed rear calipers, parking brake shoes inside the rotor, one-time-use pad wear sensors, torque-plus-angle bracket bolts
3. FCP Euro - BMW F30 standard front brake replacement - sliding caliper on non-M Sport cars, guide pins, pad wear sensor routing, piston compressed with a caliper tool
4. FCP Euro - BMW 335i brake calipers - non-M Sport 335i caliper for 340mm rotors; caliper repair kits with pistons available
5. FCP Euro - Front BMW E90 brake replacement - E90 brakes use electronic pad wear sensors replaced along with pads and rotors
6. NRS Brakes - Stuck, seized or leaking caliper guide - causes and symptoms of seized and leaking calipers, rebuild vs replace, two-year fluid flush recommendation
7. EBC Brakes - Bluestuff NDX pads - fast-street and track-day intended use, high friction rating, 200-mile street bed-in