1970 PONTIAC FIREBIRD TRANS AM

Typical onset: Original transmissions often fail between 60,000-90,000 miles, but age is a bigger factor than mileage

Symptoms: Delayed engagement when shifting into drive or reverse, Burnt transmission fluid smell and dark/black fluid color, Slipping between gears especially under throttle, Overheating after highway driving or spirited acceleration

Fix: Full rebuild of the TH400 with updated clutches, bands, and seals. Plan for 12-16 hours labor. Original oil coolers often clog or leak, requiring replacement. Most shops recommend upgrading to an auxiliary cooler while you're in there.

Estimated cost: $2,800-4,200

Typical onset: Typically seen at 80,000-120,000 miles on original engines, but abuse accelerates this significantly

Symptoms: Heavy knocking sound from lower engine that increases with RPM, Dropping oil pressure especially at idle when hot, Metallic debris in oil filter and pan, Loss of power and rough running

Fix: Requires complete engine disassembly and machine work. Crankshaft needs grinding, new bearings, often new pistons and rings. Machine shop time plus 20-30 hours labor for removal, rebuild, and reinstall. Many owners opt for complete rebuilt long block instead.

Estimated cost: $5,500-9,000

Typical onset: Original gaskets fail between 50,000-80,000 miles; aftermarket replacements every 40,000-60,000 depending on quality

Symptoms: White smoke from exhaust on startup, Coolant loss with no visible external leaks, Oil contaminated with coolant (milky appearance on dipstick), Overheating and poor heater performance, Bubbling in radiator or overflow tank when running

Fix: Both heads must come off for proper repair. Always have heads checked for warping and cracks while off—these 455 heads crack between valve seats. Plan for head resurfacing. 14-18 hours labor plus machine work. Replace intake manifold gaskets at same time.

Estimated cost: $2,200-3,800

Typical onset: 60,000-100,000 miles with original flat-tappet cam, accelerated by modern low-zinc oils

Symptoms: Valve train clatter and ticking that doesn't quiet down when warm, Loss of power and poor throttle response, Rough idle and misfiring under load, Metal particles in oil

Fix: Camshaft replacement requires intake manifold removal, lifter valley access, and timing chain replacement while you're in there. Modern flat-tappet cams require break-in oil with zinc additives. 12-16 hours labor. Many upgrade to roller cam setup to prevent recurrence.

Estimated cost: $2,000-3,500

Symptoms: Hard starting especially when hot, Hesitation and stumbling during acceleration, Stalling at idle or when coming to stops, Fuel smell from carburetor area

Fix: Complete fuel system cleaning required: tank removal and cleaning or replacement, new fuel lines (original steel lines rust through internally), carburetor rebuild on the Rochester Quadrajet, new fuel pump and filter. If car has sat, expect varnished passages. 8-12 hours labor.

Estimated cost: $1,200-2,400

Symptoms: Running hot in traffic or on hot days (over 210°F), Coolant boiling over from radiator cap, Heater blows cold when idling but hot when moving, Temperature gauge climbs steadily in slow traffic

Fix: 455 runs hot by design. Original radiators are marginal—most need re-coring or replacement with upgraded 3-row core. Water pump, thermostat, and all hoses should be replaced. Verify fan clutch operation. Shroud must be intact. Many add electric fans. 6-10 hours labor.

Estimated cost: $1,400-2,600

Symptoms: Excessive vibration at idle in gear, Clunking when shifting or accelerating hard, Engine movement visible when blipping throttle, Driveline shudder during hard launches

Fix: All rubber mounts turn to mush after 50+ years. Replace all engine and transmission mounts as a set—mixing old and new creates uneven loading. Simple job but access is tight. 3-5 hours labor.

Estimated cost: $400-700