1978 PLYMOUTH TRAIL DUSTER

Typical onset: 80,000-150,000 mi

Symptoms: Rattling on cold start for 2-3 seconds then quiets, Erratic idle or hesitation under acceleration, Check timing with light—jumps around or retarded 5-10 degrees, Metal shavings in oil filter on high-mileage engines

Fix: Replace timing chain, gears, and tensioner as a set; requires front accessory removal and timing cover pull. Good time for water pump and front seal. 4-6 hours labor for experienced tech, 8+ for DIY first-timer.

Estimated cost: $400-800

Typical onset: 60,000-100,000 mi

Symptoms: Clunking or popping on tight turns, especially in 4WD, Vibration at highway speed that changes with steering input, Grease weeping from knuckle seals or u-joint caps, Play in axle shaft when you grab tire and push/pull

Fix: Replace axle u-joints (require press or torch), knuckle bearings, and seals—one side takes 3-4 hours, budget a full day for both sides if neglected. Knuckle bearings need preload set correctly or you'll be back in six months.

Estimated cost: $600-1,200

Symptoms: Hard starting when hot, floods easily, Fuel smell in cab or engine bay after sitting, Hesitation or bog off idle, stumbles on acceleration, Gas mileage drops from 12 mpg to 8-9 mpg

Fix: Carter BBD (2-bbl) or Thermoquad (4-bbl) carbs have rubber parts that dry out and float needles that wear. Full rebuild kit is 2-3 hours on the bench; adjust float level carefully or you'll have running issues. Ethanol fuel accelerates deterioration.

Estimated cost: $250-500

Typical onset: 70,000-120,000 mi

Symptoms: Pedal slowly sinks to floor with constant pressure, Brake fluid level drops weekly, no visible external leaks, Rear brakes lock prematurely on gravel or wet pavement, Spongy pedal that doesn't improve with bleeding

Fix: Master cylinder internal seals fail and leak into the booster; proportioning valve (mounted on frame rail) also develops internal leaks. Replace both together—master is 1.5 hours, valve adds another hour plus full system bleed.

Estimated cost: $400-700

Symptoms: Body sags or leans to one side when parked, Doors won't latch or gaps change seasonally, Visible rust perforation at cab corners, rear wheel arches, or floor pans, Body mount bolts spin or pull through rusted frame crossmembers

Fix: This is the platform killer. Inspect frame thoroughly at body mounts, spring hangers, and steering box mount. If surface rust only, treat and paint; if structural (holes >1 inch, flaking), budget welding/plating at 10-20 hours or walk away. Body mounts alone are $300 parts, 4-6 hours labor.

Estimated cost: $800-3,500

Symptoms: Fuel gauge reads empty, quarter, or full constantly regardless of fill level, Fuel smell near tank or filler neck, especially after fill-up, Hard starting after sitting overnight—fuel drains back, Visible rust streaks below tank straps

Fix: Steel tank sits behind rear axle, rusts from the top down (road salt splash). Sending unit float arm corrodes or grounds out. Drop tank (2 hours), inspect for pinhole leaks; if rusty inside, replace don't seal-coat. Sending unit is separate or comes with new tank.

Estimated cost: $450-900

Typical onset: 80,000-140,000 mi

Symptoms: More than 2 inches of free play at wheel rim before tires move, Wandering on highway, constant steering corrections needed, Clunk when reversing direction of steering input, Leaking gear oil from sector shaft seal

Fix: Saginaw manual or power steering box wears at sector shaft bushings and worm gear. Adjustment screw can take up some slack (30 minutes), but worn boxes need rebuild or replacement—3-4 hours labor to R&R, align steering wheel, and bleed power steering if equipped.

Estimated cost: $350-800