The 1970 Skylark is a solid GM A-body with typical mid-century durability issues—the TH350/TH400 transmissions are bulletproof until they're not, and the Rochester carburetors need regular attention. Engine longevity varies wildly based on previous owner care.
TH350/TH400 Transmission Failure
Common · high severityTypical onset: 80,000-140,000 mi
Symptoms: Slipping between gears especially 1-2 shift, Delayed engagement when shifting to Drive or Reverse, Burnt transmission fluid smell and dark red/brown fluid color, Clunking when downshifting
Fix: Full rebuild required—clutch packs, bands, seals, filter, and torque converter inspection. Expect 12-16 labor hours for removal, rebuild, and reinstall. Transmission mounts typically need replacement during this job.
Estimated cost: $1,800-3,200
Rochester Carburetor Issues (2GC/Quadrajet)
Common · medium severitySymptoms: Hard starting when cold or hot, Rough idle and stalling at stop signs, Black smoke from exhaust indicating rich condition, Hesitation on acceleration, Fuel leaking from carburetor base gasket
Fix: Rebuild kit installation with 3-4 hours labor—replace all gaskets, accelerator pump, needle/seat, and adjust float levels. Often discover warped base requiring machining. Ethanol fuel deteriorates rubber components faster than original specs.
Estimated cost: $350-650
Oil Consumption and Worn Piston Rings
Occasional · high severityTypical onset: 90,000-150,000 mi
Symptoms: Blue smoke on startup or during acceleration, Burning through 1+ quart of oil every 500-800 miles, Low compression readings below 110 psi on multiple cylinders, Carbon buildup visible on spark plugs
Fix: Requires engine-out rebuild or ring replacement if cylinders aren't scored. Expect 24-32 hours for proper job including head removal, honing, new rings, bearings inspection, gaskets, and reassembly. Many shops recommend full rebuild at this point given age.
Estimated cost: $2,800-5,500
Crankshaft Main and Rod Bearing Wear
Occasional · high severityTypical onset: 100,000-180,000 mi
Symptoms: Deep knocking sound from bottom end that increases with RPM, Metal shavings or glitter in oil during changes, Low oil pressure at idle below 10 psi, Sudden catastrophic failure if ignored
Fix: Engine must come out for proper crank inspection and machine work. Crank typically needs 0.010-0.020 undersize grind, new bearings all around, and complete gasket set. Plan 30-40 hours including removal, machine shop time coordination, and reassembly.
Estimated cost: $3,500-6,000
Fuel System Varnish and Clogging
Common · medium severitySymptoms: Intermittent fuel starvation especially under load, Engine dies after 15-20 minutes of operation, Hard starting after sitting for days, Weak or erratic fuel pump pressure below 5 psi
Fix: Replace fuel filter, inspect and clean fuel tank of varnish buildup, replace rubber fuel lines that have degraded, and test/replace mechanical fuel pump. Modern ethanol fuel accelerates deterioration. Expect 4-6 hours for thorough system service.
Estimated cost: $400-800
Transmission Oil Cooler Line Failure
Occasional · medium severityTypical onset: 60,000-120,000 mi
Symptoms: Transmission fluid leak at radiator or along frame rail, Low transmission fluid leading to slipping, Rusted or cracked steel lines especially at fittings, Fluid loss often noticed as spots on garage floor
Fix: Replace both steel lines from transmission to radiator—originals rot from inside out. Use pre-bent replacement lines or have custom lines made. Installation is 2-3 hours including fluid refill and leak check.
Estimated cost: $250-500
Buy one if the engine runs smooth and transmission shifts clean—but budget $2-3K for deferred maintenance on any 50+ year old car regardless of current condition.
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.