The 1979 LeMans rides on GM's reliable A-body platform, but suffers from typical late-'70s emission-choked engine wear and TH200/TH350 transmission problems. The carburetion and smog equipment from this era cause more headaches than the solid chassis underneath.
TH200 Automatic Transmission Failure
Common · high severityTypical onset: 70,000-110,000 mi
Symptoms: slipping between gears especially 1-2 shift, delayed engagement when shifting to drive, whining noise in gear, no forward gears but reverse works
Fix: The TH200 (metric 200) was GM's weakest automatic and grenades regularly behind even the small V8s. Rebuild requires 8-12 hours, but most shops recommend swapping to a TH350 from a heavier LeMans or similar A-body which adds fabrication time for crossmember and driveshaft work. Core TH200 rebuild is 10-14 hours labor.
Estimated cost: $1,400-2,200
Quadrajet Carburetor Issues and Vacuum System Leaks
Common · medium severityTypical onset: 60,000-140,000 mi
Symptoms: rough idle and stalling when warm, black smoke on acceleration, hesitation off idle, high fuel consumption, won't pass emissions
Fix: The Rochester Quadrajet needs full rebuild kits by now — accelerator pump worn, power piston springs collapsed, float needles sticking. Combined with cracked vacuum lines to EGR, AIR pump, and EVAP systems. Carb rebuild is 3-4 hours, chasing vacuum leaks adds another 2-3 hours of diagnostic time.
Estimated cost: $450-850
Engine Bearing Failure (All V8s)
Occasional · high severityTypical onset: 90,000-150,000 mi
Symptoms: knocking sound on cold start that quiets when warm, low oil pressure at idle, metallic rattling under load, milky oil from coolant intrusion on some
Fix: The Pontiac 301 and Chevy 305 especially see spun rod bearings from marginal oil pressure and worn cam bearings. Olds 403 eats main bearings. Full bearing replacement requires engine pull, hot tank, crank polish — 18-24 hours labor. Often becomes full rebuild when you're that deep.
Estimated cost: $2,800-4,500
Intake Manifold Gasket Leaks
Common · medium severityTypical onset: 80,000-120,000 mi
Symptoms: coolant loss with no visible leak, white smoke on startup, rough idle, oil looks milky or chocolate pudding texture
Fix: The composite intake gaskets fail from heat cycling, leaking coolant into cylinders or oil passages. Pontiac and Olds V8s worse than Chevy units. Requires manifold removal, careful deck surface cleaning, new gaskets and sometimes valley pan. 5-7 hours labor including coolant flush.
Estimated cost: $550-900
Rear Main Seal Leakage
Occasional · low severityTypical onset: 100,000+ mi
Symptoms: oil drips from bellhousing area, wet spots under car after sitting, oil consumption without visible valve cover leaks
Fix: Two-piece rope seals leak as they age and dry out. Proper fix requires transmission removal for access — 8-10 hours labor. Many owners live with it and keep a drip pan underneath since the leak is usually slow. Speedi-Sleeve conversion recommended during replacement.
Estimated cost: $650-1,100
Frame Rust and Body Mount Rot
Common · medium severitySymptoms: clunking over bumps, body shifting relative to frame, visible rust perforation near rear spring mounts, doors misaligned
Fix: Northeastern and rust-belt cars see serious frame rail rot ahead of rear axle and at body mount points. Body bushings disintegrate from age. Inspection critical before purchase — frame repairs require welding and plating (12-20 hours), body mounts are 4-6 hours. Structural integrity issue.
Estimated cost: $800-2,500
Buy one if the frame is solid and it has the TH350 transmission; budget $2,000 for deferred maintenance and carburetor/emission system sorting 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.