The 1979 AMC Spirit is a badge-engineered Gremlin with typical AMC drivetrain durability but plagued by specific issues related to engine oiling, transmission mounts, and fuel delivery. The 258ci I6 is more robust than the troublesome GM-sourced 151ci I4.
Premature Main and Rod Bearing Failure (258ci I6)
Common · high severityTypical onset: 80,000-120,000 mi
Symptoms: Heavy knocking on cold start that quiets when warm, Low oil pressure at idle when hot, Metallic rattling under acceleration, Oil contamination with bearing material visible
Fix: Requires complete bottom-end teardown with crank inspection and polishing or replacement. Main and rod bearings plus oil pump typically needed. 16-22 hours labor for in-chassis rebuild, more if crank needs machining.
Estimated cost: $2,800-4,500
Collapsed Transmission Mount (All)
Common · medium severityTypical onset: 60,000-90,000 mi
Symptoms: Severe clunking when shifting into drive or reverse, Driveline vibration at cruising speeds, Transmission tail housing contacting crossmember, Shifter feels loose or misaligned
Fix: The rubber mount deteriorates rapidly, especially with fluid contamination. Requires transmission support and crossmember removal. 1.5-2.5 hours labor. Inspect for transmission case cracks where mount bolts on.
Estimated cost: $180-320
Chronic Vapor Lock and Fuel Starvation
Common · medium severitySymptoms: Engine stalls or refuses to restart when hot, Stumbling and hesitation in summer heat, Hard starting after short heat-soaked stops, Fuel smell from evaporating gas in engine bay
Fix: Factory fuel line routing passes too close to exhaust manifold. Requires rerouting fuel lines with heat shielding, adding inline filter, and sometimes relocating mechanical fuel pump or adding electric pump. 3-5 hours for proper rework.
Estimated cost: $350-650
Piston Ring Failure (151ci I4 "Iron Duke")
Common · high severityTypical onset: 50,000-80,000 mi
Symptoms: Excessive blue smoke on startup and acceleration, Oil consumption exceeding 1 quart per 500 miles, Loss of compression across multiple cylinders, Carbon buildup causing spark plug fouling
Fix: The GM 151 is notorious for ring land failures and cylinder bore wear. Requires complete tear-down with cylinder honing or boring, new pistons and rings. 18-24 hours labor. Often more economical to swap in a 258ci I6.
Estimated cost: $2,200-3,800
Torqueflite 904/998 Transmission Bushing Wear
Occasional · medium severityTypical onset: 90,000-140,000 mi
Symptoms: Delayed engagement into gear (2-3 seconds), Harsh or erratic shifts between gears, Transmission whine in neutral that changes with gear selection, Fluid leaking from front pump area
Fix: Front pump bushing and output shaft bushing wear cause excessive clearances. Requires transmission removal and full rebuild with new bushings, seals, clutches, and bands. 12-16 hours labor.
Estimated cost: $1,800-2,900
Crankshaft Flex and Harmonic Balancer Failure (258ci I6)
Occasional · high severityTypical onset: 100,000-150,000 mi
Symptoms: Visible wobble of harmonic balancer at idle, Severe vibration that worsens with RPM, Rubber separating from balancer outer ring, Timing marks become unusable for adjustment
Fix: The 258 develops harmonic issues as balancer rubber deteriorates. Requires removal and replacement with quality balancer. If ignored, can cause crank snout damage requiring full engine rebuild. 2-3 hours labor if caught early.
Estimated cost: $280-450
Fuel Tank Sending Unit and Pump Access Issues
Occasional · low severitySymptoms: Fuel gauge reads full constantly or erratic, Gauge drops to empty with 1/4 tank remaining, Fuel starvation on inclines with partial tank, Fuel pump noise increases or pump fails
Fix: Sending unit float arms corrode and pumps fail, but tank must be dropped for access—no top access panel. Requires fuel system depressurization, tank drop, and unit replacement. 3-4 hours labor.
Estimated cost: $380-620
Buy only with the 258ci I6 and documented maintenance history—budget $2,000-3,000 for deferred engine and transmission work on any example.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.