Parts for your 2009 Subaru Forester-Brake booster

2009 Subaru Forester brake booster — what it does and how to look after it

Yes, the 2009 Subaru Forester is fitted with a vacuum brake booster. This is confirmed by the Subaru Factory Service Manual for the 2009 Forester (SH) under the Brake section covering the Vacuum Brake Booster, the Subaru electronic parts catalogue listing a complete booster assembly and check valve for this model, and common workshop databases that specify a vacuum-assisted booster for 2009 Forester variants. So, the brake booster is absolutely relevant to this vehicle.

On this Forester, the brake booster uses engine vacuum to multiply pedal force, so the driver gets strong stopping power without standing on the pedal. Inside the round canister on the firewall is a diaphragm that reacts to vacuum on one side and atmospheric pressure on the other. A one-way check valve and hose connect it to the intake manifold, making sure there’s reserve assist even if the engine momentarily loses vacuum.

There’s no fixed replacement interval for a booster, but smart servicing includes quick checks at every brake inspection (or at least annually/20,000 km):

• Listen for a constant hiss near the pedal or under the bonnet — a sign of a vacuum leak.
• Check the vacuum hose and one-way check valve for cracks, softness, or reversed orientation.
• Look for brake fluid seeping from the rear of the master cylinder into the booster — fluid inside the booster ruins the diaphragm.
• With the engine off, press the brake pedal a few times to deplete vacuum. Hold the pedal, start the engine, the pedal should sink slightly as assist returns.

If replacement is needed, a competent DIYer or technician will:

1. Deplete vacuum (engine off, pump pedal), disconnect the battery, and remove the vacuum hose and check valve.
2. Unbolt the master cylinder from the booster. If brake lines must be disturbed, be prepared to bleed the system.
3. Undo the pedal clevis pin under the dash and the booster-to-firewall nuts, then lift the booster out.
4. Fit the new booster with a fresh grommet/gasket, confirm pushrod length is to spec, adjust pedal free play, and verify brake light switch operation.

Afterwards, check for a firm, progressive pedal with the engine running, verify there are no vacuum leaks, and road test in a safe area. If the pedal is rock hard and stopping distances blow out, don’t drive it — sort the booster or vacuum supply first. A healthy booster keeps this Forester’s brakes confident and consistent on Aussie and Kiwi roads.

Popular questions about 2009 Subaru Forester brake boosters

How can someone tell if the brake booster is failing?
Common clues include a hard brake pedal, longer stopping distances, a hissing noise when pressing the pedal, or a rough/fast idle that changes with brake application. If brake fluid has leaked from the master cylinder into the booster, assist may be intermittent and the booster will usually need replacing.

Is the 2009 Forester’s booster vacuum or electric?
It’s a vacuum-assisted unit. Engine manifold vacuum feeds the booster through a one-way check valve and hose mounted on the firewall side. There’s no electric or hydraulic brake assist on this model year Forester.

Is it safe to drive with a bad brake booster?
Not recommended. The car will still stop, but the pedal will be very firm and stopping distances can increase a lot, especially in an emergency. If the pedal feels abnormally hard or there’s a clear vacuum leak, get it checked or towed to avoid a risky situation.