The 1971 Centurion sits on GM's full-size B-body with the robust TH400 transmission and either the 350 or 455 V8. These are fundamentally stout platforms, but neglect and age catch up—expect transmission cooling issues, oil consumption from worn rings, and lower-end bearing concerns on higher-mileage examples.
Transmission Oil Cooler Failure Leading to Contamination
Common · high severityTypical onset: 80,000-150,000 mi
Symptoms: Milky or strawberry-colored transmission fluid, Erratic shifting or delayed engagement, Coolant level dropping without visible external leaks, Transmission overheating or slipping under load
Fix: The internal radiator-mounted cooler corrodes and allows coolant into ATF. Requires cooler replacement, radiator inspection or replacement, full fluid flush with filter, and often a transmission rebuild if contamination has circulated. 8-12 hours labor if trans needs rebuild, 3-4 hours if caught early.
Estimated cost: $800-3,500
Piston Ring Wear and Oil Consumption (455 V8)
Common · medium severityTypical onset: 100,000-140,000 mi
Symptoms: Blue smoke on startup or during acceleration, Needing 1+ quart of oil every 500-800 miles, Fouled spark plugs, Loss of power and compression on cylinder leak-down test
Fix: The 455's large bores and soft factory rings wear faster than smaller engines. Requires full teardown, hone, new rings, bearings, gaskets, machining if cylinders are scored. 20-28 hours labor for a proper ring job with bearing inspection.
Estimated cost: $2,800-4,800
Main and Rod Bearing Wear (Both Engines)
Occasional · high severityTypical onset: 120,000+ mi
Symptoms: Deep knocking sound from lower engine, worse under load, Low oil pressure at idle (below 10 psi warm), Metallic debris in oil filter or pan, Sudden catastrophic noise followed by engine seizure
Fix: Neglected oil changes and wear lead to spun bearings. Requires crankshaft removal, inspection, possible machining or replacement, new bearings, and full lower-end rebuild. If crank is damaged, add 6-8 hours and $400-800 for grinding or replacement. 18-24 hours labor minimum.
Estimated cost: $3,200-6,000
Transmission Mount Collapse
Common · medium severityTypical onset: 60,000-100,000 mi
Symptoms: Clunking when shifting into gear or accelerating, Excessive driveline vibration at highway speed, Visible sag or tearing of rubber mount, Transmission tail housing sitting too low
Fix: Rubber fatigues and tears, letting the TH400 drop and misalign the driveshaft. Easy fix—drop crossmember, replace mount. 1-1.5 hours labor.
Estimated cost: $150-300
TH400 Transmission Internal Wear (Clutches and Seals)
Occasional · high severityTypical onset: 90,000-130,000 mi
Symptoms: Slipping in 2nd or 3rd gear under throttle, Delayed or harsh 1-2 shift, No reverse or intermittent reverse engagement, Burnt ATF smell and dark, gritty fluid
Fix: The TH400 is tough but not immortal—clutch packs wear, seals harden, and shift quality degrades. Full rebuild with clutches, bands, seals, filter, torque converter inspection. 8-12 hours labor, more if converter needs replacement.
Estimated cost: $1,800-3,200
Carburetor Flooding and Fuel System Varnish
Occasional · low severitySymptoms: Hard starting when hot, Gas smell in engine bay or garage, Rough idle, black smoke, poor fuel economy, Leaking fuel from carburetor base or accelerator pump
Fix: Ethanol fuel and sitting periods cause needle/seat issues and varnish in the Rochester carbs. Requires rebuild kit, float adjustment, fuel filter replacement. 2-3 hours labor.
Estimated cost: $250-500
Solid old-school iron if maintained, but plan for a trans cooler upgrade and eventual engine freshening on any example over 100k—great cruiser if you're handy or have a trusted mechanic.
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.