The 1975 Buick Century is a mid-size A-body that suffers primarily from deteriorating drivetrains due to age and pre-emissions robustness meeting 1970s emission strangling. Transmission and engine wear dominate the problem list, while the chassis itself remains relatively bulletproof.
TH350/TH400 Automatic Transmission Failure
Common · high severityTypical onset: 80,000-140,000 mi
Symptoms: Slipping between gears, especially 1-2 shift, Delayed engagement when shifting into Drive or Reverse, Burnt transmission fluid smell and dark red/brown fluid, Harsh or banging shifts under acceleration
Fix: Complete transmission rebuild with new clutch packs, bands, seals, and torque converter. 8-12 hours labor. At this age, most units need full teardown due to worn bushings and hardened seals from sitting or poor fluid maintenance.
Estimated cost: $1,800-2,800
Worn Main and Rod Bearings (All Engines)
Common · high severityTypical onset: 100,000-150,000 mi
Symptoms: Heavy knocking or rumbling from bottom end, especially on cold start, Low oil pressure at idle (below 10 psi), Metallic debris in oil or on magnetic drain plug, Knocking that worsens with throttle application
Fix: Engine must come out for proper bearing replacement. Crank typically needs turning at machine shop, new bearings, plus all gaskets and seals while apart. 16-24 hours total labor including R&R. Many owners opt for full rebuild or junkyard replacement at this point.
Estimated cost: $2,500-4,200
Deteriorated Engine Mounts and Transmission Mount
Common · medium severitySymptoms: Excessive engine movement visible when revving in Park, Clunking when shifting from Park to Drive, Vibration through firewall and floorboards at idle, Transmission linkage binding or feeling notchy
Fix: Replace all three mounts (two engine, one transmission). Original rubber has usually turned to stone or crumbled by now. 2-4 hours labor depending on accessibility and exhaust removal needs.
Estimated cost: $300-550
Carburetor Issues (All V8s)
Common · medium severitySymptoms: Hard starting when cold, requires excessive cranking, Flooding with raw gas smell after sitting, Rough idle and stalling at stop signs, Black smoke from tailpipe under acceleration
Fix: Rochester 2-barrel or 4-barrel carbs typically need complete rebuild with new float, needle/seat, accelerator pump, and all gaskets. Ethanol fuel has destroyed original rubber components. 3-5 hours for proper rebuild and adjustment.
Estimated cost: $400-700
Timing Chain Stretch and Wear (350/455 V8)
Occasional · medium severityTypical onset: 120,000+ mi
Symptoms: Rattling from timing cover on cold start that quiets after warmup, Loss of power and poor fuel economy, Engine backfiring through carburetor, Difficult to set proper ignition timing, keeps drifting
Fix: Replace timing chain, gears, and dampener. Requires front cover removal. Should replace oil pump and front seal while accessible. 6-8 hours labor.
Estimated cost: $600-1,000
Leaking Transmission Oil Cooler Lines
Common · medium severitySymptoms: Red transmission fluid puddles under front of car, Fluid dripping from radiator connection points, Low transmission fluid requiring frequent top-offs, Rust-through on steel lines near radiator
Fix: Replace both steel lines from transmission to radiator. Original lines rust from road salt and age. Pre-bent replacements available. 2-3 hours labor, requires draining some coolant and transmission fluid.
Estimated cost: $250-450
Worn Piston Rings and Cylinder Glazing
Occasional · medium severityTypical onset: 130,000+ mi
Symptoms: Blue smoke on startup and deceleration, Excessive oil consumption (quart per 500-800 miles), Loss of compression leading to hard starting, Carbon buildup visible on spark plugs
Fix: Requires complete engine disassembly, cylinder honing or boring, new rings on all pistons, plus valve job while apart. Most opt for full rebuild at this stage. 20-30 hours labor.
Estimated cost: $3,000-5,000
Buy only if the drivetrain has documented recent rebuilds or you're prepared to invest $3-5K in mechanicals within the first year - but the platform itself is solid and parts are still available.
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.