The 1970 LeMans represents GM's A-body at its peak before emissions strangled performance, but 50+ years of age means you're dealing with worn drivetrains, deteriorated bushings, and metal fatigue across the board. These are project cars now, not daily drivers.
Automatic Transmission Failure (TH350/TH400)
Common · high severityTypical onset: 80,000-120,000 mi original, but many are beyond this now
Symptoms: Slipping between gears, especially 1-2 shift, Delayed engagement when shifting to Drive or Reverse, Burnt transmission fluid smell, dark brown or black fluid, Whining or grinding noises during acceleration
Fix: Full rebuild required in most cases due to worn clutch packs, hardened seals, and valve body issues. Expect 12-16 hours labor for removal, rebuild, and reinstallation. Cooler lines often corroded and need replacement simultaneously.
Estimated cost: $2,200-3,800
Engine Bearing Failure (All V8 Options)
Occasional · high severityTypical onset: 100,000+ mi or unknown maintenance history
Symptoms: Deep knocking sound from bottom end, worse under load, Low oil pressure at idle (below 10 psi warm), Metallic debris in oil pan during changes, Sudden catastrophic failure if ignored
Fix: Requires complete engine disassembly to replace main and rod bearings. Crankshaft often needs machining if wear exceeded .010 inch. Most shops recommend full rebuild at this point given age and disassembly labor. 25-35 hours for proper bearing replacement or full rebuild.
Estimated cost: $3,500-6,500
Carburetor Degradation (Rochester 2GC/Quadrajet)
Common · medium severityTypical onset: Not mileage-driven, age and ethanol damage
Symptoms: Hard starting when cold, excessive cranking required, Rough idle, stalling at stop lights, Poor fuel economy, black smoke from exhaust, Hesitation or stumble during acceleration, Fuel leaking from carburetor base or externally
Fix: Ethanol fuel destroys original rubber components and corrodes zinc castings. Professional rebuild with modern ethanol-resistant kit runs 3-5 hours including removal and tuning. Many owners opt for aftermarket replacement instead.
Estimated cost: $450-900
Front Subframe and Control Arm Bushing Deterioration
Common · medium severitySymptoms: Clunking over bumps from front suspension, Wandering or loose steering feel on highway, Uneven tire wear on inside or outside edges, Visible cracking or complete separation of rubber bushings
Fix: Original rubber bushings are toast after 50+ years regardless of mileage. Upper and lower control arm bushings, strut rod bushings, and sway bar links all need replacement. 8-12 hours labor, requires alignment afterward.
Estimated cost: $1,200-2,000
Brake Master Cylinder and Line Failure
Occasional · high severitySymptoms: Soft or spongy brake pedal that goes to floor, Brake fluid leaking at master cylinder or wheel cylinders, Pulling to one side during braking, Single-chamber systems lose all braking if seal fails
Fix: Master cylinder internals corrode and seals fail with age. Original single-chamber systems are dangerous by modern standards. Steel brake lines rust through at frame rails and flex points. Budget 6-8 hours for master cylinder and full hard line replacement to all four corners.
Estimated cost: $800-1,500
Fuel System Contamination and Leakage
Common · high severitySymptoms: Fuel smell inside cabin or around vehicle, Visible fuel leaks at tank, pump, or rubber lines, Engine starvation or stuttering at highway speeds, Rust particles clogging fuel filter repeatedly
Fix: Original steel tanks rust from inside out, rubber fuel lines crack and leak, fuel pumps fail. This is a fire hazard—address immediately. Tank removal and replacement with new sending unit, all rubber lines, filter, and mechanical pump runs 8-10 hours.
Estimated cost: $900-1,600
Rear Axle Bearing and Seal Failure (10-bolt or 12-bolt)
Occasional · medium severityTypical onset: 90,000+ mi or abuse history
Symptoms: Growling or humming from rear end that changes with speed, Gear oil leaking at axle tubes or pinion seal, Clicking during turns if limited-slip clutches are worn, Excessive backlash or clunking when changing throttle
Fix: Axle bearings and seals wear out, pinion seals leak. Requires axle removal and bearing press work. If carrier bearings or ring-and-pinion are worn, full rebuild needed with setup time. 6-10 hours for bearings/seals, 12-18 for full rebuild.
Estimated cost: $700-2,800
Buy only if you have mechanical skills, a backup vehicle, and realistic expectations—this is a 50+ year old car that will need constant attention and expensive engine/trans work is nearly inevitable.
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.