The 1970 Buick GS is a muscle car built on GM's A-body platform with either a 350 or 455 cubic inch V8. These are 50+ year old performance vehicles where original drivetrain components, rubber mounts, and fuel delivery systems are at end-of-life, requiring systematic rebuilding rather than simple repairs.
TH400/TH350 Automatic Transmission Failure
Common · high severityTypical onset: original transmissions typically fail between 80,000-150,000 miles, but many survivors have unknown history
Symptoms: Slipping between gears, especially 2nd to 3rd shift, Delayed engagement when shifting into drive or reverse, Burnt transmission fluid smell and dark/metallic fluid, Hard shifting or no movement in one or more gears
Fix: Complete rebuild of TH400 or TH350 transmission with new clutch packs, bands, seals, and torque converter. Expect 12-18 hours labor for removal, rebuild, and reinstallation. Most survivors need this within first year of ownership due to age.
Estimated cost: $2,200-3,800
Engine Bottom End Wear (Crankshaft Bearings and Ring Failure)
Common · high severityTypical onset: 100,000+ miles on original engines, but neglected engines fail earlier
Symptoms: Heavy rod knock at idle that worsens with RPM, Excessive oil consumption (more than 1 quart per 500 miles), Low oil pressure (below 10 psi at idle when warm), Blue smoke on acceleration indicating worn piston rings, Metallic debris in oil filter or pan
Fix: Requires engine removal and complete bottom-end rebuild or short/long block replacement. Machine work includes crankshaft grinding, cylinder boring/honing, new pistons, rings, bearings, and rod reconditioning. 25-35 hours labor for complete job including removal and reinstallation.
Estimated cost: $4,500-7,500
Deteriorated Transmission and Engine Mounts
Common · medium severityTypical onset: not mileage-driven, age-related failure at 50+ years
Symptoms: Severe clunking when shifting from park to drive or reverse, Visible engine movement when revving in neutral, Excessive vibration at idle transmitted through chassis, Transmission tunnel heat and noise increase
Fix: Replace all engine mounts (typically 3) and transmission mount. Original rubber has hardened and cracked. Transmission mount replacement requires supporting transmission and removing crossmember. 3-5 hours labor total.
Estimated cost: $400-750
Fuel Delivery System Degradation
Common · medium severityTypical onset: not mileage-driven, age and ethanol damage
Symptoms: Hard starting after sitting, especially when hot, Stumbling or hesitation during acceleration, Fuel smell in garage or visible leaks at sender or lines, Engine stalling at idle or low speed, Rust particles in fuel filter
Fix: Replace fuel tank sender unit, all rubber fuel lines, fuel filter, and fuel pump. Steel lines often have internal rust. Many owners opt for full tank replacement and hardline replacement. Mechanical fuel pump rebuild or replacement. 6-10 hours labor depending on line condition.
Estimated cost: $800-1,800
Transmission Oil Cooler Line Failure
Occasional · high severityTypical onset: not mileage-driven, age and vibration-related
Symptoms: Transmission fluid leak at radiator connections or along frame rail, Rapid transmission fluid loss leading to slipping or overheating, Rust perforation on steel cooler lines near frame brackets, Coolant contamination in transmission (milky fluid) if internal radiator leak occurs
Fix: Replace both transmission cooler lines from transmission to radiator. Original steel lines corrode from outside-in. If radiator has internal leak, transmission fluid mixes with coolant requiring full flush and potential transmission damage. 2-4 hours labor for line replacement only.
Estimated cost: $300-600
Carburetor Issues (Rochester Quadrajet or 2-barrel)
Occasional · medium severityTypical onset: not mileage-driven, ethanol fuel damage and age
Symptoms: Poor fuel economy (single digits in city driving), Black smoke from exhaust indicating rich condition, Rough idle or high idle that won't come down, Hesitation or flat spot during acceleration, Fuel leaking from accelerator pump or bowl gaskets
Fix: Complete carburetor rebuild with ethanol-resistant gaskets, new accelerator pump, needle/seat, and float adjustment. Many original Quadrajets have warped throttle shafts requiring bushing. 4-6 hours for removal, rebuild, and proper tuning.
Estimated cost: $450-900
Buy only if you have $8,000-12,000 budgeted for immediate mechanical restoration and patience for a project—these are not drive-anywhere muscle cars without major investment.
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.