1966 BUICK GS

Typical onset: 80,000-120,000 mi

Symptoms: Delayed or harsh shifting, especially when hot, Transmission slipping in 2nd or 3rd gear, Burnt fluid smell and dark red/brown fluid color, Loss of reverse or complete failure to engage

Fix: The ST-300 two-speed or ST-400 three-speed automatics overheat easily due to failed oil coolers or clogged lines. Expect 12-16 hours for a proper rebuild with new clutches, bands, seals, and servicing the cooler lines. Many survivors have never had fluid changed, accelerating wear.

Estimated cost: $2,200-3,800

Typical onset: 100,000+ mi

Symptoms: Deep knocking sound at idle that worsens under load, Low oil pressure readings below 20 psi at hot idle, Metallic debris in oil pan during changes, Sudden catastrophic failure if ignored

Fix: The Nailhead's vertical valves and unique oiling system make it sensitive to oil neglect. Worn main and rod bearings require a complete bottom-end rebuild or crankshaft R&R. Figure 25-35 hours for pull, machine work, bearing install, and reinstall. Many shops sub out machine work adding 1-2 weeks.

Estimated cost: $4,500-7,500

Typical onset: 60,000-90,000 mi

Symptoms: White smoke from exhaust on cold start, Coolant consumption without visible leaks, Milky or foamy oil on dipstick or filler cap, Overheating under load or highway speeds

Fix: The Nailhead's combustion chamber design and age-hardened gaskets lead to head gasket leaks, often both sides simultaneously. Resurfacing heads recommended. 18-24 hours labor for both sides with proper cleanup and torque sequence. Use modern composite gaskets, not original style.

Estimated cost: $1,800-2,800

Typical onset: 80,000+ mi

Symptoms: Blue smoke on deceleration or startup, Excessive crankcase pressure venting from breather, Oil consumption above 1 quart per 500 miles, Poor compression readings below 120 psi across multiple cylinders

Fix: Original cast rings wear and cylinders glaze over decades of heat cycles. Full ring job requires bore honing or over-boring if cylinder taper exceeds .010 inches. 30-40 hours for proper teardown, machine work, piston/ring fitment, and reassembly. Often done during bottom-end work.

Estimated cost: $3,500-5,500

Symptoms: Hard starting when hot, especially after sitting 15-30 minutes, Stumbling or hesitation during acceleration, Stalling at idle after warmup, Fuel smell from carburetor area due to percolation

Fix: Ethanol fuel and long storage periods leave varnish throughout the fuel system. Inline filters clog quickly, carburetors need complete rebuild with modern gaskets, and steel fuel lines often rust internally. 6-10 hours for full system flush, carburetor rebuild, and tank cleaning if neglected.

Estimated cost: $600-1,200

Symptoms: Clunking when shifting from Park to Drive or Reverse, Excessive driveline vibration at highway speeds, Visible sagging or misalignment of transmission tailshaft, Difficulty shifting or linkage binding

Fix: Original rubber mounts are 55+ years old and completely deteriorated on most survivors. Crossmember often rusted, especially in salt states. 3-4 hours to properly support transmission, replace mount and inspect/treat crossmember rust. Alignment check recommended after.

Estimated cost: $300-600