2015-2019 Subaru Outback Brake Caliper Problems and Replacement

By Core Brake Parts Tech Team — Circleville, OH warehouse

Most brake caliper problems on a 2015-2019 Subaru Outback are not a failed caliper at all - they are seized slide pins, a piston that no longer retracts cleanly, or a hose that holds pressure. The tell-tale signs are a pull to one side, one wheel much hotter than the others, and pads worn unevenly on the same axle. Fix the root cause, replace calipers in axle pairs when one has truly failed, and bleed the system properly afterward.

How the brakes work on the 2015-2019 Outback

This fifth-generation Outback uses disc brakes at all four corners. When Subaru introduced the 2015 model, its press kit noted that all models moved to ventilated rear discs in place of the solid rear discs used before, and that the 2.5i picked up the larger brake hardware previously reserved for the six-cylinder car. That matters when you buy parts: rotors and pads are trim-sensitive, so always match by year, engine and trim.

The front and rear calipers are sliding (floating) designs. The caliper body rides on two guide pins in a bracket bolted to the knuckle. When you press the pedal, hydraulic pressure pushes the piston out, the inner pad contacts the rotor, and the caliper slides on its pins to pull the outer pad in. When you release the pedal, the square-cut piston seal pulls the piston back slightly and the caliper relaxes on its pins. Anything that stops that small movement - rust, dried grease, a torn boot, trapped pressure - causes drag.

The Outback also has an electronic parking brake, but on this generation it does not live in the rear caliper. The factory service information describes an electric actuator that pulls cables to a small set of parking brake shoes inside the hat of each rear disc rotor. In practice that means the rear caliper pistons are serviced like any conventional sliding caliper, while the parking shoes and the drum surface inside the rotor hat are a separate inspection item whenever the rear rotors come off.

Symptoms of a caliper problem

• Pull under braking. If one front caliper is sticking or not applying fully, the car will steer toward the side that is doing more work.
• One hot wheel and a burning smell. After a normal drive, a dragging brake leaves one wheel noticeably hotter and can give off a hot, acrid smell. Do not touch the rotor - hold your hand near the wheel or use an infrared thermometer.
• Uneven pad wear. An inner pad far thinner than the outer pad on the same wheel usually points to seized slide pins. One side of the car wearing much faster than the other points to a piston or hose problem on that side.
• Soft or sinking pedal and fluid on the wheel. A leaking piston seal or bleeder shows up as wetness on the inside of the wheel and a dropping fluid level in the reservoir. That caliper must be replaced, not cleaned.
• Clunk or knock over bumps. Worn guide pin bushings or loose hardware let the caliper rattle in its bracket.
• A car that coasts poorly. A light drag often shows up as a vehicle that slows quickly when you lift off the throttle, along with a dip in fuel economy.

What actually causes it

A trade tech tip from Brake and Front End sums up the slider-caliper failure list well: the caliper cannot move freely because of bent or binding mounting pins, worn slides, bent or damaged brackets, swollen or hardened guide seals, or missing lubrication. On an Outback that sees winter road salt, corroded guide pins and rust-jacked pad abutments are by far the most common version of this.

A piston that will not return is a different problem. CARDONE's technical bulletin on sticking caliper pistons points out that residual hydraulic pressure is often the real cause. Their test is simple: if the piston stays applied, crack the bleeder. If the piston then releases, the caliper itself is fine and something upstream is trapping pressure - a twisted or internally collapsed rubber brake hose, a kinked metal line, a faulty master cylinder, or a misadjusted pushrod or brake light switch. Replacing the caliper in that case will not fix the drag.

Old fluid plays a part too. Brake fluid absorbs moisture over time, which corrodes pistons and bores from the inside. CARDONE recommends changing brake fluid every two years to prevent premature brake failure; your owner's manual gives Subaru's own interval and the correct fluid specification, which is also printed on the reservoir cap.

Check for the 2017 caliper bolt recall first

Before you buy anything for a 2017 Outback, run the VIN through the NHTSA recall lookup. Recall 16V576000 covers certain 2017 Outback vehicles built from June 20, 2016 to June 23, 2016 that may have improperly tightened attaching bolts for the front left and right brake calipers, the wheel hubs, and the right stabilizer clamp. A loose caliper bolt can cause a knock or abnormal brake noise, and in the worst case let the caliper move out of position. The inspection and any bolt replacement are done by a Subaru dealer at no cost.

The fix: which parts to replace

If the bleeder test shows the caliper itself is at fault, or the piston is leaking or pitted, replace the caliper. Replace calipers in pairs on the same axle so both sides apply with equal force; a brand-new caliper on one side and a tired one on the other is a recipe for a pull. Browse our replacement brake calipers and confirm fit by year, engine and trim.

A caliper that has been dragging has almost always overheated the pads and rotor on that corner. Glazed pads and a heat-spotted or thin rotor should be replaced with it. For the front axle, a matched 2015-2019 Subaru Outback front brake kit from Power Stop gives you rotors and pads sized for the car in one order. You can also shop brake pads and brake rotors separately.

Replace at the same time:

• Pad hardware. New abutment clips and guide pin boots from a brake hardware kit are cheap insurance against the next seizure.
• Rubber brake hose. If the bleeder test pointed to trapped pressure, or the hose is cracked or swollen, replace it. See brake hoses.
• Brake fluid. Any caliper swap opens the system. Flush with the fluid type on the reservoir cap rather than simply bleeding the one corner.
• Rear parking shoes (when doing the rear). With the rear rotors off, check the parking brake shoes and the drum surface inside the rotor hat for wear and contamination.

How hard is the job?

A caliper swap on this Outback is a moderate DIY job with basic hand tools, a torque wrench, and a way to bleed the brakes. The sequence is: loosen the lug nuts, lift and support the car on stands, remove the wheel, disconnect the brake hose at the caliper (have new sealing washers ready), remove the caliper and bracket bolts, fit the new caliper with fresh pads and lubricated pins, torque every fastener to the value in the factory service manual, then bleed the system in the order the service manual specifies.

Three Outback-specific notes. First, because the parking brake is a separate shoe system, the rear caliper pistons press back like a normal sliding caliper - but do not operate the parking brake switch while a rear rotor or caliper is off the car. Second, the Outback's stability control and Hill Holder functions work through the same hydraulic system, so a thorough bleed matters; if the pedal is still soft after a manual bleed, a shop with a scan tool can cycle the ABS hydraulic unit during bleeding. Third, bed in the new pads before normal driving so they transfer an even layer onto the rotors.

If the job involves a seized bracket bolt, a rounded bleeder, or a rusted metal line, it stops being a quick afternoon and becomes a shop job.

Frequently Asked Questions

Can I replace just one caliper on my Outback?

You can, but pairs on the same axle are the better repair. Two calipers of the same age and condition apply evenly, which prevents a pull and uneven pad wear.

Do I need a scan tool to do the rear brakes on a 2015-2019 Outback?

Not for the calipers and pads. On this generation the electronic parking brake works through cable-operated shoes inside the rear rotor hat, not a motor on the caliper, so the rear pistons compress like a standard sliding caliper. Keep the parking brake off while the rear is apart.

How do I know if it is the caliper or the brake hose?

With the wheel dragging, open the bleeder. If the piston relaxes and the wheel turns freely, pressure was trapped upstream, often in the rubber hose. If it stays tight with the bleeder open, the caliper piston or slide pins are the problem.

Is my 2017 Outback part of the brake caliper bolt recall?

Only certain 2017 Outbacks built June 20-23, 2016 are covered by recall 16V576000. Enter your VIN at nhtsa.gov or ask a Subaru dealer; the inspection is free.

Should I replace pads and rotors when I replace a caliper?

If the old caliper was dragging, yes on that axle. Overheated pads glaze and rotors develop hard spots, and reusing them undercuts the new caliper.

Remanufactured or new calipers?

Both work when built to OE specification. What matters most is that the caliper matches your trim, comes with the correct bracket if you are replacing it, and that both sides of the axle are done together.

Sources

1. Subaru U.S. Media Center - 2015 Outback press kit - ventilated rear discs on all models, 2.5i gets larger brakes, Brake Assist, Hill Holder and VDC
2. NHTSA recall data - 2017 Subaru Outback - recall 16V576000, front caliper, hub and stabilizer clamp bolts, June 20-23, 2016 production
3. Subaru Outback service information - Parking Brake - electric actuator and cables operating parking shoes inside the rear disc
4. CARDONE ProTech PT18-0002 - Sticking Caliper Piston Cause and Solution - bleeder test, residual pressure causes, two-year fluid change recommendation
5. Brake and Front End - Slider-style caliper tech tip - causes of binding sliding calipers and high-temperature lubricant on pins