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Front brake hose cracks and leaks

Mitsubishi ran two separate United States recall campaigns on the front flexible brake hoses of this generation. The first says the wheel-side hose can crack when the steering is at full lock and the suspension at full travel — the two things that happen together every time the truck is manoeuvred hard or driven off pavement. The second, a much smaller campaign, covers cracking of the lower hoses. Either way the result is the same: fluid escapes from one front circuit, the pedal travels further than it should, and the truck stops on less than it was designed to stop on. These are the original rubber hoses on a truck that is now decades old, so age and heat have done their own work on top of whichever defect the campaign described. Both campaigns are United States ones filed with NHTSA; a truck imported from another market was never part of them, and nothing here says what any other market's authority required. Whatever the paperwork says, flexible brake hoses are a wear item with a service life, and on a truck this age they are inspected on their condition, not on their recall history.

Gen 21992–1994USSafety-criticalTechnical service bulletin (TSB)

Do not driveNo lo maneje

Safety notice — Brakes.

This affects a safety-critical system. Reference material only: for safety-critical work, consult a qualified mechanic.

Esto afecta un sistema crítico para la seguridad. Material de referencia únicamente: en trabajos críticos para la seguridad, consulte a un mecánico calificado.

Symptoms

  • The brake warning lamp comes on and stays on
  • The pedal sinks slowly while you hold steady pressure at a stop
  • The fluid reservoir keeps dropping without the pads being worn out
  • A wet, oily film on the inside of one front wheel or on the inner fender

Likely causes

  1. Cracked flexible hose on the wheel side of the front axle
  2. Cracked lower front hose
  3. Leaking caliper piston seal
  4. Leaking master cylinder or its bulkhead seal

Diagnostic steps

  1. With the truck safely raised and supported, look along both front hoses for cracks, bulges and wet patches, and wipe the area dry so a fresh leak showsPoints toCracked flexible hose on the wheel side of the front axle · Cracked lower front hoseRules outLeaking master cylinder or its bulkhead seal
  2. Have someone turn the steering to full lock both ways while you watch the wheel-side hose flex, and look into the folds of the bendPoints toCracked flexible hose on the wheel side of the front axleRules outCracked lower front hose
  3. Peel back the caliper piston boot and look for fluid behind itPoints toLeaking caliper piston sealRules outCracked flexible hose on the wheel side of the front axle · Cracked lower front hose
  4. Look under the reservoir and at the bulkhead where the master cylinder passes through, and check the carpet below the pedal for dampPoints toLeaking master cylinder or its bulkhead sealRules outLeaking caliper piston seal

Fix paths

Replace both front hoses and bleed the system

$–$$Difficulty 3/5

Hoses are replaced in pairs, never one side alone: the two have aged together, and a fresh hose beside a cracked one gives the truck an uneven front end under hard braking. Bleed the whole system afterwards and check the pedal before the truck moves.

Replace the caliper on the leaking side

$$Difficulty 3/5

If the fluid is coming from behind the piston boot rather than from the hose, the hose is not the fault. Fluid that has run over a pad has contaminated it, so pads on that axle are replaced with the caliper.

Sources

  1. NHTSA safety recall 96V143001 (Mitsubishi) — front wheel-side brake hose can crack under full-lock steering and full suspension travelManufacturer literaturearchived copy
  2. NHTSA safety recall 00V226001 (Mitsubishi) — front lower brake hoses can crackManufacturer literaturearchived copy
  3. NHTSA owner complaint database — 1992 Mitsubishi MonteroReference workarchived copy