1991-1993 Mitsubishi 3000GT Brake Caliper Problems and Replacement

By Core Brake Parts Tech Team — Circleville, OH warehouse

Most brake caliper problems on a 1991-1993 Mitsubishi 3000GT come down to age: sticking pistons, seized slide pins on the floating calipers, torn dust boots and moisture-laden fluid in a system that may be over thirty years old. Before you buy a caliper, identify which brake system your car has, because the VR-4 uses a fixed four-piston front caliper while the base and SL do not, and check the front brake hoses, which were the subject of a safety recall on these model years.

Which Calipers Your 3000GT Has

Every first-generation 3000GT came with four-wheel ventilated disc brakes, but the hardware is not the same across the lineup. The 1991-1993 cars were sold as the base coupe, the midrange SL and the VR-4. The base and SL are front-wheel drive; the VR-4 is the twin-turbo car with all-wheel drive and four-wheel steering. Anti-lock brakes were standard on the SL and VR-4 and not available on the base car in these years.

The VR-4 is the only one of the three listed with four-piston front calipers. Published stock specifications for the twin-turbo AWD cars (the VR-4 and its Dodge Stealth R/T Turbo twin) are below.

This matters when ordering. The 1994 and later VR-4 moved to larger rotors and a twin-piston rear caliper, and the caliper outside dimensions changed with it, so a caliper listed only as "3000GT VR-4" may be the later part. Match both the model year and the trim. The base and SL use floating front calipers that are a different part from the VR-4 four-piston unit, and the two are not interchangeable without changing knuckles, hubs and rotors as well.

Symptoms of a Failing Caliper

A caliper that is going bad rarely fails all at once. Watch for these signs:

• Pulling to one side under braking or while cruising. One caliper is dragging or one is not applying fully.
• One wheel much hotter than the others after a drive, often with a hot, burnt smell. A piston that will not retract keeps the pad on the rotor.
• Uneven pad wear. On a floating caliper, an inner pad worn far more than the outer points to seized slide pins. On the VR-4 fixed caliper, uneven wear across one pad usually means one piston pair is sticking.
• Fluid on the inside of the wheel or tire and a dropping reservoir level. A leaking piston seal is a replace-now item.
• A soft or sinking pedal, or the brake warning lamp coming on.
• A car that coasts poorly when rolled in neutral on level ground, and worse fuel economy than it used to get.

What Causes Caliper Problems on These Cars

On a car this old, the root cause is usually the fluid and the rubber. Brake fluid absorbs moisture over time, and that moisture corrodes the caliper bores and pistons from the inside. Torn dust boots let road grit and water reach the piston and seal from the outside. Once the piston surface pits, it drags in the seal and will not retract cleanly. Cardone, one of the largest caliper remanufacturers, recommends changing brake fluid every two years to prevent premature brake failure, advice many 3000GTs that sat in storage never got.

Not every dragging brake is a bad caliper, though. Cardone's technical bulletin on sticking pistons says that if a newly installed caliper still will not release, open the bleeder: if the piston then releases, the caliper is fine and something upstream is holding pressure. The usual suspects are a twisted or internally restricted rubber brake hose, a kinked metal line, a faulty proportioning or combination valve, a failing master cylinder, a misadjusted booster pushrod, or a misadjusted brake light or cruise switch.

The Front Brake Hose Recall

Hoses deserve extra attention on this car. NHTSA campaign 96V143002 covered 3000GTs built from August 1, 1990 through November 4, 1993: under full steering lock with full suspension travel, the left or right front wheel-side brake hose could crack and leak fluid, turning on the brake warning lamp and reducing braking effectiveness. Dealers replaced both front wheel-side hoses with revised assemblies. Even on a car that had the recall done, those hoses are now decades old. If you are replacing a front caliper, replace the flexible hose on that corner at the same time; see our brake hoses. You can also check any VIN for open recalls on nhtsa.gov.

Fixing It: Rebuild or Replace

You have two routes:

• Replace with a loaded or remanufactured caliper. This is the fastest fix and the right call when the bore is pitted. Replacement units are available in our brake calipers collection, including Cardone remanufactured calipers. Replace calipers in pairs on an axle so both sides clamp evenly.
• Rebuild with seals and boots. Workable if the bore and pistons are clean and smooth. If you find pitting or rust on the piston's sealing surface, a seal kit will not cure it.

What to replace at the same time:

• Pads and rotors. A dragging caliper usually overheats the pads and can glaze or unevenly wear the rotor. See brake pads and brake rotors, or a matched set such as the 1991-1993 Mitsubishi 3000GT front and rear brake kit.
• Hardware. Clips, shims and slide-pin boots on the floating calipers; a brake hardware kit is inexpensive insurance.
• Flexible hoses, for the recall history above.
• Brake fluid. Flush the whole system, not just the corner you opened. Use the fluid specified on the master cylinder cap or in the owner's manual.

How Hard Is the Job?

For a home mechanic with jack stands and basic tools, a caliper swap on a first-generation 3000GT is a moderate job. The floating calipers on the base and SL come off in the usual way: bracket or slide bolts, then the hose fitting. The VR-4's fixed four-piston front caliper bolts rigidly to the knuckle and is heavier, and the packaging on the twin-turbo AWD car is tighter, but the process is similar. Torque the caliper mounting bolts and hose fittings to the values in the factory service manual rather than guessing, and use new sealing washers on banjo fittings.

Bleeding is where most DIY jobs go wrong. The SL and VR-4 have ABS, so bleed in the sequence the service manual gives and keep the reservoir from running dry, or you may end up chasing air in the hydraulic unit. Once the air is out, bed the new pads in with a series of moderate stops before any hard driving.

Frequently Asked Questions

Do all 1991-1993 3000GTs have four-piston front calipers?

No. Only the VR-4 came with four-piston front calipers. The base and SL use a floating front caliper, and the parts are not interchangeable.

Can I put 1994 and later VR-4 calipers on a 1991-1993 car?

Not as a direct swap. The 1994 and later cars use larger rotors, the caliper outside dimensions changed to fit them, and the rear moved to a twin-piston caliper. Buy the part listed for your model year.

Should I replace both calipers or just the bad one?

Replace them in pairs on the same axle. A new caliper on one side and a 30-year-old one on the other invites a pull and uneven pad wear.

My new caliper still drags. Is it defective?

Maybe not. Crack the bleeder: if the piston releases, pressure is being held upstream, most often by a restricted rubber hose, a kinked line, a faulty valve or master cylinder, or a misadjusted pushrod or brake light switch.

Was my 3000GT part of the brake hose recall?

The recall covered cars built from August 1990 through November 1993, which spans the 1991-1993 model years. Enter your VIN on nhtsa.gov to confirm, and consider replacing the front hoses regardless of history given their age.

Sources

1. Stealth 316 - Brake Upgrade Options - 1991-1993 twin-turbo AWD caliper types, piston bores, rotor sizes, 1994 changes
2. 3000GT Online - 1991-1993 Specs - four-piston front calipers on VR-4 only, ABS availability by trim
3. Consumer Guide - 1991-99 Mitsubishi 3000GT - trims, drivetrain, four-wheel discs standard, hose recall
4. NHTSA Campaign 96V143002 (via Justia) - front brake hose recall details and production dates
5. Cardone ProTech - Sticking Caliper Piston Cause and Solution - upstream causes of a dragging caliper, two-year fluid change