The 1966 Mercury Comet shares Ford's Falcon platform with solid build quality, but suffers from typical 1960s Ford small-block timing chain wear, carburetor issues, and suspension bushings that disintegrate with age. The 289/390 V8s are generally reliable if maintained, while the I6 is bulletproof but slow.
Timing Chain Stretch and Failure (289/390 V8)
Common · high severityTypical onset: 80,000-120,000 mi
Symptoms: rattling from front of engine on cold starts, erratic idle and loss of power, backfiring through carburetor, won't start after sitting—jumped timing
Fix: Replace timing chain, gears, and tensioner. Requires front cover removal, oil pan dropped or loosened. 6-8 hours labor for experienced tech. Original nylon-toothed cam gears disintegrate—mandatory upgrade to steel.
Estimated cost: $800-1,400
Front Suspension Upper Control Arm Bushings
Common · medium severitySymptoms: clunking over bumps, wandering steering and poor alignment retention, uneven tire wear on inside edges, visible cracking or missing rubber in bushings
Fix: Replace all four upper control arm bushings. Requires press or ball-joint tool. Alignment mandatory after. 3-4 hours labor plus alignment.
Estimated cost: $500-800
Autolite 2100/4100 Carburetor Flooding and Leaking
Common · medium severitySymptoms: fuel odor in garage or while driving, hesitation and stumbling on acceleration, black smoke from exhaust, hard starting when hot, fuel leaking from accelerator pump or bowl gaskets
Fix: Full rebuild with quality kit (not cheap eBay junk), set float levels precisely, replace accelerator pump. 2-3 hours labor. Ethanol fuel eats original gaskets.
Estimated cost: $350-600
Rear Leaf Spring Shackles and Bushings
Common · low severitySymptoms: squeaking or groaning from rear on bumps, rear axle appears cocked or misaligned, sagging rear end, visible rust or seized shackle bolts
Fix: Replace shackles, bushings, and bolts. Rusted bolts often break—plan for extra penetrant time or cutting. 2-3 hours labor.
Estimated cost: $300-500
Steering Box Wear and Leakage
Occasional · medium severityTypical onset: 100,000+ mi
Symptoms: excessive play in steering wheel (more than 2 inches), fluid leaking from steering box seals, groaning when turning at low speed, wandering on highway requiring constant correction
Fix: Rebuild possible but most techs swap in reman unit. Adjustment helps temporarily. 3-4 hours labor including alignment check.
Estimated cost: $450-750
Generator/Alternator Voltage Regulator Failure
Occasional · medium severitySymptoms: ammeter showing discharge or overcharge, dim lights at idle or overly bright lights, dead battery after short trips, burnt voltage regulator smell
Fix: External regulator easy to replace (10 minutes). Many owners upgrade to alternator if still running generator. If alternator, test and replace regulator or alt itself. 0.5-1.5 hours.
Estimated cost: $80-350
Transmission Kickdown Linkage Binding (C4/C6 Automatics)
Occasional · low severitySymptoms: transmission won't downshift for passing, delayed or harsh downshifts, stuck in higher gear under load, linkage visibly rusted or disconnected at carburetor
Fix: Clean, lubricate, and adjust kickdown rod and bellcrank at transmission and carb. Sometimes needs replacement if bent. 1-1.5 hours labor.
Estimated cost: $120-250
Floor Pan and Torque Box Rust (Northern Cars)
Common · high severitySymptoms: visible rust holes in driver/passenger floor, soft or crunchy metal around rear leaf spring mounts, jack won't hold because of torque box rot, water leaks into interior
Fix: Requires patch panels or full floor replacement, welding skills mandatory. Torque boxes structural—must be solid. 12-20+ hours labor depending on extent.
Estimated cost: $1,500-4,000
Solid driver-grade classic if rust-free and timing chain has been done—avoid project cars with structural rust unless you weld, and budget $2K for deferred maintenance on any barn find.
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.