Parts for your 1999 Mitsubishi Pajero-Brake booster

1999 Mitsubishi Pajero Brake Booster — What It Does and How to Look After It

Based on Mitsubishi’s workshop documentation for the late-’90s Pajero (Group 35: Brakes/Power Brake) and the Mitsubishi ASA electronic parts catalogue for 1999 Pajero variants, this model is factory-fitted with a vacuum brake booster mounted on the firewall behind the master cylinder. Petrol engines use manifold vacuum, diesel models use a dedicated vacuum pump and check valve to supply the booster. So yes, the brake booster is absolutely relevant to the 1999 Mitsubishi Pajero.

The brake booster’s job is simple but crucial: it uses engine vacuum to multiply the driver’s pedal effort, giving strong, progressive braking without needing to mash the pedal. If the booster or its vacuum supply goes crook, the pedal goes hard, stopping distances blow out, and braking feels wooden.

During routine servicing on a 1999 Pajero, a few easy checks make a big difference:

• Listen for a constant hiss at the pedal area and feel for a hard pedal — both can hint at a torn diaphragm or leaking hose.
• Inspect the large vacuum hose and one-way check valve for cracks, loose clamps, or oil contamination. Diesels especially rely on a healthy vacuum pump and valve.
• Look for brake fluid tracking into the booster from the rear of the master cylinder, a failing master can leak into the booster and ruin it.
• Perform the classic booster test: with the engine off, pump the pedal until it’s firm, hold it, then start the engine. A slight pedal drop means the booster is working.

When replacement’s on the cards, owners will want to plan a straightforward swap: the master cylinder typically comes off the booster studs, the pedal clevis pin is removed inside the cabin, and the booster lifts away. On many Pajeros the lines can be carefully shifted aside so the system doesn’t need to be opened, if the lines are cracked open, a full bleed is required afterwards. Always set the booster pushrod-to-master-cylinder clearance per spec in the workshop manual to avoid dragging brakes or long pedal travel. Fresh grommets, a new check valve where needed, and correct torque on the mounting nuts finish the job nicely.

Look after the vacuum hose, keep the brake fluid clean, and sort any vacuum faults promptly — the Pajero’s booster will deliver easy, confidence-inspiring stops for years.

Popular questions about 1999 Mitsubishi Pajero brake boosters

How can someone tell if the brake booster is failing on a 1999 Pajero?
A hard brake pedal, longer stopping distances, and a steady hissing noise near the pedal are the classic giveaways. Another sign is the pedal not dropping slightly when the engine starts after being pumped firm with the engine off. If it’s a diesel, also check the vacuum pump output and the one-way valve.

Is the diesel Pajero’s brake booster different from the petrol version?
Functionally they do the same job, but diesels rely on a dedicated vacuum source rather than manifold vacuum. That means the health of the vacuum pump, hose, and check valve is just as important as the booster itself on diesel models.

Is it safe to drive with a failed brake booster?
The brakes will still work, but pedal effort skyrockets and stopping distances increase, especially in traffic or downhill. It’s not recommended — organise repair or towing rather than risking reduced braking assist.