The 1977 Buick Century rides on GM's A-body platform with a reliable small-block V8 or Buick V6, but the TH200/TH350 automatics show their age after decades of use, and the 231 V6 from this era develops internal engine wear patterns that lead to expensive rebuilds.
TH200 Transmission Failure (V6 models)
Common · high severityTypical onset: 80,000-120,000 mi
Symptoms: slipping between gears, especially 1st-2nd, delayed engagement when shifting to Drive, transmission fluid burned smell or dark color, whining noise in gear
Fix: The TH200 (M-29) was GM's weakest automatic and fails predictably. Rebuild runs 8-12 hours labor, but most shops recommend replacement with a junkyard TH350 swap (stronger) which adds 4-6 hours for crossmember and linkage mods. Cooler lines often corroded and need replacement simultaneously.
Estimated cost: $1,800-3,200
Buick 231 V6 Premature Engine Wear
Common · high severityTypical onset: 90,000-140,000 mi
Symptoms: excessive oil consumption, 1+ quart per 500 miles, blue smoke on startup and acceleration, low oil pressure at idle when hot, knocking or ticking from crankcase
Fix: The even-fire 231 in '77 still had soft camshaft lobes and undersized main bearings that wore prematurely. Machine work, piston rings, bearings, cam, and gaskets run 18-24 hours. Many owners opt for short block replacement (12-16 hours) or salvage long blocks to avoid core machining costs.
Estimated cost: $2,400-4,500
Transmission Mount Collapse
Common · medium severitySymptoms: clunk when shifting from Park to Drive or Reverse, excessive drivetrain movement felt through floorboards, vibration at idle in gear, visible transmission sag when inspected on lift
Fix: Rubber mounts deteriorate badly after 40+ years regardless of mileage. Replacement is straightforward: 1.5-2 hours labor with transmission support. Often done alongside transmission cooler line work since you're already under there.
Estimated cost: $150-300
Carburetor Float and Needle Valve Issues
Occasional · medium severitySymptoms: fuel odor after sitting, especially in hot weather, hard starting when hot, flooding and black smoke, fuel dripping from air cleaner base
Fix: Rochester 2-barrel carbs (V6) and Quadrajet (V8) develop stuck float needles and hardened float materials from ethanol fuel exposure. Rebuild kits run 2-3 hours labor but originals often had pot metal castings that don't respond well to modern fuel. Many techs suggest aftermarket Edelbrock conversions (4-5 hours with tuning).
Estimated cost: $300-800
Transmission Cooler Line Corrosion
Common · medium severitySymptoms: transmission fluid puddles under front of vehicle, pink or red fluid on radiator or frame rails, low transmission fluid level, overheating transmission
Fix: Steel cooler lines rust through at bends and mounting points, especially in rust-belt cars. Replacement with pre-bent or custom brake line runs 2-3 hours including radiator cooler inspection. Always replace both lines and flush the system to clear debris.
Estimated cost: $250-500
Crankshaft Thrust Bearing Wear (231 V6)
Occasional · high severityTypical onset: 100,000+ mi
Symptoms: metallic knock that changes with clutch pedal (manual) or hard acceleration, excessive crankshaft endplay measurable with dial indicator, oil pressure fluctuation, eventually progresses to catastrophic failure
Fix: Thrust bearing surface on #3 main wears from clutch abuse or defective bearing design. Requires full teardown, crank measurement, and possibly crank grinding or replacement. If caught early, bearing replacement runs 16-20 hours; if crank is damaged, add machine work or replacement crank costs.
Estimated cost: $2,000-3,800
Buy a V8 model with TH350 if you want reliability; the 231 V6 and TH200 combo will drain your wallet within two years of ownership.
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.