1970 PONTIAC FIREBIRD

Typical onset: 80,000-120,000 mi original, or anytime if neglected

Symptoms: Slipping on 1-2 or 2-3 shifts, especially under load, Delayed engagement when shifting to Drive or Reverse, Burnt transmission fluid smell, dark or metallic fluid, No movement in any gear after warm-up

Fix: Full rebuild required in most cases—remove transmission, disassemble, replace clutch packs, bands, seals, bushings, and torque converter if damaged. Expect 12-16 hours labor for removal, rebuild, and reinstall. TH350 rebuilds are slightly cheaper than TH400 due to parts availability.

Estimated cost: $2,200-3,800

Typical onset: 100,000+ mi, or anytime with oil neglect

Symptoms: Deep knocking noise from crankcase that increases with RPM, Low oil pressure at idle, especially when hot, Metallic debris visible in oil filter or pan, Sudden catastrophic failure with connecting rod through block

Fix: Requires engine removal, crankshaft inspection/machining, new main and rod bearings, often new oil pump. If crank is damaged beyond .030 undersize, replacement needed. With engine out, expect 24-32 hours total for R&R, disassembly, machine work wait time, and reassembly. Many owners opt for full rebuild at this point.

Estimated cost: $3,500-6,500

Typical onset: 90,000-140,000 mi

Symptoms: Blue smoke on startup that clears after warm-up, Excessive oil consumption, 1 quart per 500-800 miles, Low compression readings across multiple cylinders, Loss of power and poor fuel economy

Fix: Short block or complete engine rebuild. Cylinders need boring/honing, new pistons and rings fitted. If cam and lifters show wear, it becomes a full rebuild. Engine removal makes the job cleaner but adds time—25-35 hours total. Some try a ring job without boring but success rate is poor on engines this old.

Estimated cost: $3,200-5,800

Symptoms: Clunking when shifting from Park to Drive or Reverse, Excessive driveline vibration at certain speeds, Visible separation or cracking of rubber mount, Transmission tailshaft sitting low or contacting crossmember

Fix: Replace transmission mount and inspect crossmember for damage. With vehicle on lift, support transmission, remove old mount, install new. Check for worn U-joints while underneath. 1.5-2.5 hours labor depending on exhaust routing and access.

Estimated cost: $180-350

Symptoms: Hard starting when hot, fuel percolation in summer, Engine stumbles or dies under acceleration, Fuel smell in cabin or visible leaks at line connections, Weak fuel pressure below 5 PSI on mechanical pump

Fix: Original steel fuel lines rust from inside out after 50 years. Replace from tank to pump and pump to carb with pre-formed stainless or nickel-copper line. Include new fuel pump, filter, and rubber hoses. 4-6 hours for complete fuel system refresh. Don't patch—do it once, do it right.

Estimated cost: $450-850

Typical onset: 70,000+ mi or after fluid neglect

Symptoms: Gear oil on inside of rear wheels or brake drums, Howling or whining noise from rear that changes with speed, Clunking on acceleration/deceleration if carrier bearings are gone, Differential cover weeping at gasket

Fix: Axle seal replacement is straightforward—pull axle shafts, replace seals and gasket, refill with fresh 80W-90. If bearings are noisy, expect to pull the center section and replace carrier bearings or pinion bearings, which requires setup and shimming. Seal job: 2-3 hours. Full bearing job: 6-8 hours.

Estimated cost: $280-1,200