Parts for your 1993 Mitsubishi Pajero-Brake booster

1993 Mitsubishi Pajero Brake Booster — What it does and how to look after it

Technical references confirm a brake booster is fitted to the 1993 Mitsubishi Pajero. The Mitsubishi Pajero NH–NJ Factory Service Manual (1991–1996), Group 35A Service Brakes, details a firewall-mounted vacuum servo (brake booster) behind the master cylinder. The Mitsubishi ASA electronic parts catalogue for 1993 Pajero (NH/NJ) also lists the booster assembly (common OEM references include MB858555 and MR205188), with variations across ABS and non-ABS trims. Haynes and Gregory’s Pajero/Montero manuals for the same generation describe identical vacuum-booster operation. So yes — this model uses a vacuum brake booster.

On the 1993 Pajero, the booster uses engine vacuum to reduce pedal effort, giving strong braking without having to stomp the pedal. Petrol engines draw vacuum from the intake manifold, diesels use a dedicated vacuum pump. Either way, the booster diaphragm multiplies pedal input and feeds that force into the master cylinder for confident stopping on-road and off the beaten track.

As part of regular servicing, it’s smart to check the booster and its vacuum supply. A quick driveway test helps: with the engine off, pump the brake a few times to deplete stored vacuum, hold pressure, then start the engine. The pedal should drop slightly — that’s the booster doing its job. If the pedal stays rock-hard, there’s likely a vacuum or booster issue.

• Common signs it’s crook: hard brake pedal, longer stopping distances, hissing at the firewall, unstable idle when the pedal’s pressed, or poor vacuum on diesels.
• Simple maintenance: inspect the vacuum hose for splits, check the one‑way valve, replace the grommet if it’s perished, and keep brake fluid off paintwork under the bonnet.
• Diesel note: verify vacuum pump output if assist feels weak, as a tired pump can mimic a bad booster.

Replacement is straightforward for a competent tech: the master cylinder is usually moved forward, the booster unbolted from the cabin side at the pedal, and the pushrod adjusted to workshop spec for correct pedal free play and brake light switch operation. Allow a couple of hours, fit a new gasket, and torque fasteners to spec from the factory manual. After any work, confirm pedal feel and road-test — safety first before heading out for more kilometres.

Does the 1993 Pajero use a vacuum or hydraulic booster?
It uses a vacuum brake booster (servo). Petrol variants draw vacuum from the manifold, diesel variants rely on a belt- or gear-driven vacuum pump. The mounting and operation are covered in the factory manual for NH/NJ models.

What’s the easiest way to test the booster at home?
With the engine off, pump the pedal several times, hold pressure, then start the engine. If the pedal sinks slightly, the booster is assisting. No change usually points to a vacuum leak, faulty check valve, or an internal booster diaphragm problem.

Should the booster be replaced if the pedal is hard but the brakes still work?
A consistently hard pedal is a warning sign. While the vehicle may still stop, braking distance increases. Inspect the hose and check valve first, if they’re good, plan a booster replacement to restore proper assist and keep it roadworthy.