Parts for your 2017 Mitsubishi Lancer-Brake booster

2017 Mitsubishi Lancer Brake Booster — Purpose, Service Tips, and Replacement

Technical sources confirm the 2017 Mitsubishi Lancer is fitted with a vacuum brake booster (also called a power brake unit/servo). The Mitsubishi Lancer (CF, 2015–2017) factory service manual lists the Power Brake Unit in Group 35 – Brakes, and the Mitsubishi ASA/OEM parts catalogue shows a dedicated brake booster/servo assembly for this model year. General repair references such as Haynes and Autodata also describe the Lancer’s vacuum‑assisted braking system. So the brake booster is very much relevant to this vehicle.

The brake booster’s job is to multiply pedal force using engine vacuum, so the driver gets strong, confidence‑inspiring braking with a light press. On the 2017 Lancer’s petrol engines, manifold vacuum does the heavy lifting via a one‑way check valve. In markets where low‑vacuum variants exist (e.g., certain diesels), a vacuum pump may supply the booster, but the everyday Aussie and Kiwi 2.0‑litre petrol models rely on intake vacuum.

There’s no scheduled replacement interval for the booster, it’s a fit‑and‑forget unit that should last years. Still, smart servicing includes a quick look and listen: check the vacuum hose and grommets for cracking, confirm the check valve only flows one way, and listen for any faint hissing at idle around the booster area under the bonnet. A hard brake pedal, longer stopping distances, or a pedal that doesn’t dip slightly when the engine starts are classic signs it’s not assisting properly. A vacuum leak can also cause rough idle or a higher idle speed when the pedal is pressed.

• Common symptoms: hard pedal, hissing from the driver’s side firewall, rough/raised idle when braking, and increased stopping distance.
• Quick driveway test: with the engine off, pump the pedal several times, hold it, then start the engine — the pedal should drop a touch if the booster’s working.

If replacement is needed, the unit sits between the pedal box and master cylinder. Many technicians unbolt the master cylinder and gently move it aside to avoid opening brake lines (reducing the chance of bleeding), but follow the factory procedure. Keep brake fluid off paint, fit the check valve in the correct orientation, and torque fasteners to spec. After installation, confirm pedal free play and height, verify vacuum assistance with the start‑up test, and road‑test safely. If the brake pipes were disconnected or the reservoir ran low, bleed the system and top up with the specified fluid shown on the cap (DOT 3 or DOT 4, as applicable).

During routine services, it’s worth inspecting the vacuum hose condition and ensuring the check valve isn’t gummed up. If the master cylinder leaks at the rear seal, repair it promptly — brake fluid inside the booster can damage the diaphragm.

Popular questions

How can someone tell if their 2017 Lancer’s brake booster is failing?
A hard pedal and longer stopping distances are the big giveaways. They might also hear a light hissing from the firewall area or notice the idle change when pressing the brake at a standstill. The simple start‑up test — pedal held, engine started — should cause a slight pedal drop, if not, assistance may be lacking.

Can a 2017 Lancer be driven with a bad brake booster?
It may still stop, but pedal effort skyrockets and braking distance grows, especially in an emergency. That’s not safe. It’s best to organise inspection and repair as soon as possible and avoid long drives until it’s sorted.

Does the brake system need bleeding when replacing the booster?
Not always. If the master cylinder is moved aside without opening the brake lines, bleeding can often be avoided. If any lines are opened or the reservoir level drops too low, bleeding is required. Always follow the factory procedure.