Front brake line chafes through at the inner fender

The rigid front brake lines pass through a hole in the inner fender. Mitsubishi's United States recall says that when a line is not centred in that hole it rubs on the edge, and the rubbing eventually opens pin holes in the wall of the line. The remedy the campaign describes is telling: a line still centred is simply bent back into place, and only a line already worn is replaced. That means the fault is progressive and silent for a long time — there is nothing to feel until the wall finally opens and pressure escapes. Owner reports filed with the same agency describe the same class of failure elsewhere on the run, with lines routed close enough to a neighbouring pipe to wear against it. On a truck of this age, corrosion works on the same lines from the outside, especially where they run behind a wheel that throws salt or coastal grit at them. A brake line that is leaking is not a defect you drive with, and finding the leak is not the same as knowing the rest of the run is sound.

Gen 2Gen 2.51997–1998USSafety-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 indicator lamp lights and does not go out
The pedal travels further than it used to before the truck slows
The fluid level falls with no wet wheel or wet caliper to explain it
A damp, dust-caked patch on the inner fender or along the frame rail

Likely causes

Rigid line worn through where it passes through the inner fender
Rigid line worn through against a neighbouring pipe or bracket
Rigid line perforated by external corrosion
Cracked flexible hose at the caliper end

Diagnostic steps

Find where each front line crosses the inner fender and look at the line where it meets the edge of the hole; check whether it sits centred or is pressed against one sidePoints toRigid line worn through where it passes through the inner fenderRules outCracked flexible hose at the caliper end
Follow each line from the master cylinder to the flexible hose, feeling for a flat spot, a bright rub mark or a soft, scaly sectionPoints toRigid line worn through against a neighbouring pipe or bracket · Rigid line perforated by external corrosionRules outRigid line worn through where it passes through the inner fender
Wipe the flexible hose dry, then have someone press the pedal hard while you watch for fluid appearing at the crimp or in a crackPoints toCracked flexible hose at the caliper endRules outRigid line perforated by external corrosion

Fix paths

Re-centre the line and protect it where it passes through

$Difficulty 2/5

Only for a line whose wall is still sound. Bend it back so it sits clear of the edge and fit a grommet or sleeve so it cannot walk back. A line that already has a worn flat is replaced, not repositioned.

Replace the damaged section of rigid line

$–$$Difficulty 4/5

New line is formed and flared to match, routed clear of anything that can rub it, and the system is bled afterwards. On a truck old enough to have corroded one line, the neighbouring lines have lived the same life — this is the moment to look at all of them. Brake lines are a safety-critical repair with a flare joint that must not weep; if you are not equipped to flare and bleed properly, this is work for a qualified mechanic.