BOXY TRUCKS
Common problems · 1986–92

Jeep Comanche MJ problems: 8 things to check

The problems owners and specialists flag most on the Jeep Comanche MJ, the repairs they end up doing and what those cost, plus the years and recalls to watch. Sourced, not scraped.

Read the full Jeep Comanche MJ guideYears to avoidBiggest tireSpecs & fluids

Jeep Comanche MJ problems to check before you buy

  1. Pull up the carpetNAXJA and Comanche Club members agree: rust is the number-one issue, and unless the truck lived in the Southwest or Southern California, expect it in the floors. Rusty seat brackets or bolts usually mean rusty floor pans below.
  2. Check where the cab meets the bed, and the railsLook hard where the bed meets the cab and where the unibody joins the rear frame. NAXJA members warn that bulging rail bottoms mean rust inside. Water also enters through the rear cab bulkhead and window; one member says more than one MJ has gone to the crusher because of it.
  3. Look for cracks and old welds on the frameComanche Club members say to inspect the frame closely for cracks or signs of weld repair, especially on trucks that hauled or towed.
  4. Bed, tailgate and taillightsThese are MJ-only parts and hard to replace. A crushed bed side or a missing tailgate costs more and takes longer to fix than a tired engine.
  5. Identify the rear axleAn oval cover usually means a Dana 35, and an angular, roughly hexagonal cover means a Dana 44, per NAXJA. A 1991–92 truck may have the Chrysler 8.25. Ask whether it's a Metric Ton truck; sellers often don't know.
  6. Renix or HO?1987–90 4.0s run Renix management, which stores no codes and is diagnosed with a multimeter. 1991–92 HO trucks have Chrysler's system and 190 hp. Both are good engines, but Renix trucks reward owners who like electrical troubleshooting.
  7. Hydraulic clutch and fuse boxOn manual trucks, check the clutch master cylinder. Comanche Club members warn a leak can drip brake fluid into the fuse box, which damages it.
  8. 2.5 or 4.0?The 4.0 is the one to have. If you buy a 2.5, Comanche Club members suggest looking for a 4.10 or 4.56 axle ratio. The AX-4 and AX-5 gearboxes behind the 2.5 won't bolt up to a 4.0.

The repairs Jeep Comanche MJ owners end up doing

REPAIRSYMPTOMSDIFFICULTYTIMECOST
Replace rusted floor pans and rockersWet carpet, rusty seat-bracket bolts, holes under the mats, crumbling rockers, and rust at the rear cab bulkhead where the bed meets the cab.4 / 5≈ A weekend per sideParts plus welding
Replace a leaking clutch master cylinderA soft or sinking clutch pedal, fluid on the firewall, or electrical faults from fluid dripping into the fuse box below. Comanche Club members also recommend checking the clutch-pedal welds, which some owners found incomplete and cracked.2 / 5≈ 1–2 hours plus bleedingA master cylinder or master kit
Hot stalls and no-starts: CPS, ballast resistor, groundsThe engine dies when hot and won't restart until it cools, cranks without spark, or the fuel pump won't run. Comanche Club owners name the crankshaft position sensor (CPS) and the Renix fuel-pump ballast resistor as the usual culprits, and say to check the body grounds first for strange electrical faults.2 / 5≈ 1–2 hoursA sensor or resistor plus your time
Reseal the oil filter adapterOil on the driver's side of the block and dripping off the crossmember. Comanche Club members warn that a bad adapter O-ring is often misdiagnosed as a rear main seal.2 / 5≈ 1–2 hoursUnder $20 in O-rings
Sort out the cooling system (and the Renix closed system)Overheating on hills or in traffic, coolant loss, or a cracked pressurized plastic coolant bottle. Comanche Club members suggest replacing the plastic bottle with an aluminum one, or converting the 1987–90 Renix closed system to the later open layout.2 / 5≈ Half a dayParts plus coolant
Rebush the rear leaf springs and shacklesClunks over bumps, a rear end that steers itself, rusted or seized shackles, or bent lower shock-mount bolts. Comanche Club owners recommend upgrading the rear lower shock mounts.3 / 5≈ Half a dayBushings, shackles and shocks
Fix or bypass the front axle disconnect (CAD)4WD that engages at the transfer case but doesn't drive the front wheels, or grinding from the front axle. Comanche Club members say to check the vacuum-operated central axle disconnect before your first trail, and to lock it in or bypass it if necessary.3 / 5≈ 2–4 hoursA manual-disconnect or 'shift-on-the-fly' kit
Cure death wobble: track bar and steeringViolent front shake after a bump at speed, wandering and clunks. The MJ front end is the XJ's, with the same weak points: the track bar, tie-rod ends, drag link and steering box.3 / 5≈ Half a dayParts plus an alignment

Each repair links to a step-by-step guide with tools, part numbers and where to buy the parts.

Jeep Comanche MJ recalls and service bulletins

Check any VIN for open recalls at nhtsa.gov/recalls ↗, or see the recall tracker.

Owner questions about Jeep Comanche MJ reliability

Where do they rust?

Under the carpet, at the rear cab bulkhead and window seals, where the bed meets the cab, and where the unibody meets the rear frame. NAXJA members say bulging rail bottoms mean rust inside.

SOURCE · NAXJA · COMANCHE CLUB
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Sourced from owners, specialists and factory documents; full sources are on the Jeep Comanche MJ guide. Verify torque figures and procedures against the factory service manual (disclaimer).

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