1979 PLYMOUTH TRAIL DUSTER

Typical onset: 80,000-140,000 mi

Symptoms: Rattling noise on cold start that disappears after warm-up, Rough idle or timing fluctuation, Hard starting or backfiring through carburetor, Check timing—if it won't stay set, chain is stretched

Fix: Replace timing chain, gears, and cover gasket. Budget 4-6 labor hours depending on accessories in the way. Strongly recommend doing oil pump and front seal at same time since you're there. Water pump too if it's original.

Estimated cost: $600-1,200

Symptoms: Stalling at idle, especially when warm, Surging or hesitation under light throttle, Black smoke or raw fuel smell—Thermoquad notorious for warped baseplate flooding, Hard cold starts even after choke adjustment

Fix: Full carburetor rebuild with quality kit runs 3-4 hours if you clean it properly. Thermoquads often need baseplate machining or replacement—many shops just swap to an Edelbrock or Holley for reliability. Adjust choke and check vacuum lines.

Estimated cost: $400-900

Symptoms: Visible rust perforation in cab corners and door sills, Soft or spongy floor under carpet—poke it with a screwdriver, Water pooling inside cab after rain, Seat mounts becoming loose due to floor rot

Fix: Patch panels are available but floor replacement often means cutting out 2-3 square feet per side and welding in new metal. Figure 8-12 hours if rust is moderate, more if frame rail ends are also compromised. This is a deal-breaker inspection point.

Estimated cost: $1,200-3,500

Typical onset: 70,000-120,000 mi

Symptoms: Gear oil dripping from front diff pinion area, Low fluid leads to whining or grinding on turns, Oil spray pattern on front driveshaft and skid plate

Fix: Replace pinion seal and check bearing preload—if preload is lost, you need pinion bearings too. Mark driveshaft position before removal. 2-3 hours if seal only, 5-6 if bearings are shot. Check ring gear backlash while you're in there.

Estimated cost: $300-800

Symptoms: Random no-start conditions, especially in heat or humidity, Misfiring under load that ignition timing won't fix, Computer module mounted on air cleaner fails—notorious weak point, Engine runs fine after sitting overnight, then cuts out when hot

Fix: Most techs bypass the Lean Burn and install standard electronic ignition conversion kit (orange box ECU, standard distributor). Takes 2-3 hours and eliminates the problem permanently. Far cheaper than chasing bad Lean Burn modules.

Estimated cost: $250-500

Typical onset: 60,000-100,000 mi

Symptoms: Hard shifting between 2WD and 4WD ranges, Shifter popping out of gear on rough roads, Grinding or clunking when engaging 4WD low, Linkage rods corroded or bent at firewall

Fix: Inspect and lubricate shift linkage at transfer case and cab mounts. Replace worn bushings and detent springs inside shifter mechanism. Allow 2-3 hours for linkage overhaul. Some owners upgrade to cable-shift kit for reliability.

Estimated cost: $200-450

Typical onset: 100,000-150,000 mi

Symptoms: Coolant loss with no external leaks, White smoke from exhaust on startup, Milky oil or oil in coolant overflow, Overheating under load after long highway runs

Fix: Head gasket replacement on the slant-six is straightforward but time-consuming due to long head and manifold removal. Plan 6-8 hours. Check head for warpage—machine if needed. Replace thermostat and hoses while you're there. These engines tolerate abuse but gaskets give up eventually.

Estimated cost: $700-1,300