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Soft Brake Pedal After DIY Pad & Rotor Change - 2017 Impreza

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Heather Y. · rep 0 · May 22, 3:15 AM · 1 replies · solved · Question

Vehicle: 2017 Subaru Impreza 2.0i Premium

I recently changed the front brake pads and rotors on my 2017 Subaru Impreza 2.0i Premium, which has about 70,000 miles. I followed a few online guides, and everything seemed to go smoothly. However, now my brake pedal feels really soft and spongy, and I have to push it almost to the floor to get decent braking power.

I didn't open any brake lines, just compressed the calipers to make room for the new pads. I've pumped the pedal a bunch of times, but it hasn't improved. I'm worried I might have introduced air into the system somehow, or maybe I missed a step.

What could be causing this soft pedal, and what's the best way to fix it? I'm a bit nervous driving it like this.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 3:15 AM

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Hi Kevin L., a soft or spongy brake pedal after a pad and rotor change is a common issue, and it almost always points to air in the brake lines. Even if you didn't open the lines directly, air can be introduced in a few ways during the process.

Here's why this happens and how to resolve it:

Causes of a Soft Brake Pedal:

  1. Air in the Brake Lines: This is the most likely culprit. When you compress the caliper pistons back into their bores, if the brake fluid reservoir was overfilled or if the cap was off, air can sometimes be drawn into the system, especially if the pedal was pressed at any point during the process without the calipers being fully installed.
  2. Improper Caliper Compression: If the caliper piston was compressed too quickly or unevenly, it could potentially cause issues, though air is far more common.
  3. Master Cylinder Issues (Less Likely): While rare after a simple pad/rotor change, a pre-existing weak master cylinder might show symptoms more clearly once the system is disturbed.
  4. Incorrect Pad Installation: If pads are not seated correctly, or if there's an issue with the caliper, it can lead to excessive pedal travel, though usually not a 'spongy' feel.

Steps to Fix (Brake Bleeding):

  1. Locate Bleeder Screws: Each caliper has a bleeder screw. You'll need a wrench that fits it (usually 10mm or 12mm), a clear hose, and a container to catch old fluid.
  2. Two-Person Job: Brake bleeding is best done with two people: one to pump the pedal and one to open/close the bleeder screw.
  3. Bleeding Procedure (Traditional Method):
    • Ensure the brake fluid reservoir is full and keep it topped up throughout the process.
    • Start with the wheel furthest from the master cylinder (usually passenger rear), then driver rear, passenger front, and finally driver front.
    • Have your helper pump the brake pedal 3-5 times and hold it down firmly.
    • While the pedal is held, open the bleeder screw for a few seconds until fluid (and any air bubbles) comes out. Close the screw before your helper releases the pedal.
    • Repeat this process until no more air bubbles are seen coming out of the bleeder screw for that caliper.
    • Move to the next caliper.

When to See a Shop:

  • Persistent Soft Pedal: If, after a thorough bleeding process, the pedal remains soft, or if you're uncomfortable performing the bleeding yourself, it's crucial to take your Impreza to a professional mechanic. They can perform a pressure bleed or diagnose if there's a more serious underlying issue like a faulty master cylinder or ABS module.
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