1975 PONTIAC FIREBIRD TRANS AM

Typical onset: 60,000-90,000 mi or any mileage if original

Symptoms: Delayed engagement into gear, Slipping between 1st-2nd or 2nd-3rd shifts, Burnt transmission fluid smell, Overheating after highway runs

Fix: Factory oil cooler is undersized for the 455's torque and these transmissions run hot. Cooler lines rust through, mounts collapse allowing driveline angle problems. Full rebuild with upgraded cooler and new mounts: 12-16 hours labor, plus parts. Many need valve body work and clutch packs.

Estimated cost: $2,800-4,200

Symptoms: Hard starting when hot, Stumbling off idle or during acceleration, Raw fuel smell, black smoke, Stalling at stops after highway driving

Fix: The Quadrajet carbs have internal plastic and rubber parts that deteriorate from ethanol fuel and sitting. Float bowls leak, accelerator pump diaphragms fail, choke pull-offs seize. Professional rebuild with ethanol-resistant kit: 4-6 hours including removal, bench work, and tuning.

Estimated cost: $650-950

Typical onset: 80,000-120,000 mi

Symptoms: Deep knocking from lower engine, especially under load, Oil pressure dropping at idle when hot, Metal shavings in oil filter, Sudden catastrophic noise and loss of power

Fix: The 455 Super Duty wasn't really a true SD in '75—Pontiac used the name but it's essentially a 455 H.O. These engines suffer rod bearing and main bearing wear from age, lack of oil changes, and running lean. Crankshaft often needs grinding or replacement. Complete rebuild: 28-35 hours labor for disassembly, machine work, and reassembly.

Estimated cost: $5,500-8,500

Symptoms: Fuel starvation under acceleration, Engine sputtering or dying after 10-15 minutes, Visible rust in fuel filter, Fuel smell in trunk or cabin

Fix: Steel fuel tanks rust from inside, rubber lines crack and weep, metal lines rust through at frame contact points. Ethanol fuel accelerates this on cars that sit. Tank replacement, new sending unit, all fuel lines, and filter: 8-12 hours labor depending on line routing.

Estimated cost: $1,200-1,800

Typical onset: 70,000-110,000 mi

Symptoms: Blue smoke on startup or deceleration, High oil consumption (quart every 500-800 miles), Reduced compression evident in cylinder leak-down test, Fouled spark plugs on one or more cylinders

Fix: Rings wear and cylinders glaze from infrequent use and short trips more than high miles. Requires cylinder honing or boring, new pistons if bore is out of spec, full ring set. If caught early, can do rings without full rebuild: 18-24 hours labor.

Estimated cost: $3,200-4,800

Typical onset: varies widely

Symptoms: One-wheel burnouts instead of both tires hooking, Chattering or clunking during tight turns, Differential whine or howl, Visible gear oil leaks from pinion seal or axle seals

Fix: The posi units wear out from abuse and old fluid. Clutch packs glaze, springs weaken. Requires diff disassembly, new clutch pack, bearings if needed, fresh gear oil with friction modifier. 6-8 hours labor.

Estimated cost: $850-1,400