Parts for your 1991 Mitsubishi Pajero-Brake booster

1991 Mitsubishi Pajero Brake Booster — Fitment, Purpose, and Service Tips

Technical references confirm the 1991 Mitsubishi Pajero is fitted with a vacuum brake booster (servo). Sources include the Mitsubishi Pajero/Montero Factory Service Manual (1991–1993, Group 35A – Brakes), Gregory’s Service and Repair Manual No. 513 (Pajero/Montero 1983–1996), and the Mitsubishi ASA electronic parts catalogue for V2/V4 series, all of which list a brake booster assembly across petrol and diesel variants (including ABS-equipped models). Petrol engines use manifold vacuum, while diesels rely on a vacuum pump to feed the booster.

On a 1991 Pajero, the brake booster sits between the pedal assembly and the master cylinder, using engine vacuum to multiply pedal force. That makes braking feel lighter underfoot and helps pull up a loaded wagon or an off-road rig with big tyres without needing a gym workout on the pedal. Whether it’s the trusty 4D56/4M40 diesel or a petrol V6, the booster’s job is the same: reduce pedal effort, keep stops consistent, and give a confident, progressive pedal feel around town and on long Kiwi and Aussie road trips.

As part of routine servicing, it’s smart to inspect the vacuum hose to the booster (including the one-way check valve), the grommet at the booster can, and the area between the master cylinder and booster for any sign of brake fluid. A weeping master cylinder can leak into the booster and ruin the diaphragm over time. Listen for a faint hiss at the pedal or from under the bonnet, and watch for a hard pedal with longer stopping distances—both are classic booster clues. With the engine off, pump the pedal a few times, hold pressure, then start the engine: a slight pedal drop indicates the booster is doing its thing.

If replacement is on the cards, go for quality OEM or reputable remanufactured units. On ABS models, take extra care with line routing and don’t let the master hang on its pipes. Bench-bleeding the master is wise if it’s been removed. New hose and a fresh check valve are cheap insurance. Given these trucks often see dusty tracks and tough kilometres, checking the booster setup every service or two (10,000–15,000 km) helps keep braking sharp and roadworthy checks stress-free.

• Common symptoms: hard pedal, longer stopping distances, hissing noise, idle change when pressing the pedal (petrol models).
• Quick wins: replace perished vacuum hose, renew the check valve, and fix any master cylinder leak promptly.

Popular questions about 1991 Mitsubishi Pajero brake boosters

What type of brake booster does the 1991 Mitsubishi Pajero use?
It uses a vacuum-assisted diaphragm booster (servo). Petrol versions draw vacuum from the intake manifold, diesels use a dedicated vacuum pump. ABS or non-ABS, the booster is still part of the system.

How can someone test the brake booster at home?
With the engine off, pump the pedal until it’s firm, hold it, then start the engine. If the pedal drops slightly, the booster has vacuum assist. Also check the vacuum hose and one-way valve, and listen for hissing around the pedal or booster can.

Is it safe to drive with a failed brake booster?
It’ll still stop, but the pedal will be very hard and stopping distances increase—especially with a loaded wagon or bigger tyres. It’s not recommended, sort the booster and vacuum supply before regular driving.