1984 PONTIAC FIREBIRD

Typical onset: 80,000-130,000 mi

Symptoms: Slipping on 3-4 upshift or complete loss of overdrive, Delayed engagement into gear from Park, Shuddering or flare-ups during light throttle acceleration, Burnt transmission fluid smell and dark brown ATF

Fix: The TH200-4R was GM's weakest overdrive automatic and the overdrive band/clutches fail predictably. Rebuild requires 12-16 hours including R&R, converter replacement, and band/clutch pack upgrades. Many shops won't warranty stock rebuilds without performance upgrades to the weak intermediate sprag and 3-4 clutches.

Estimated cost: $2,200-3,800

Typical onset: 60,000-120,000 mi

Symptoms: Rough idle, stalling when warm, Hesitation on acceleration, flat spots in power delivery, Hard starting after sitting for days, Check engine light with codes for lean/rich conditions or TPS

Fix: The 1984 Crossfire TBI system (dual throttle bodies) has failing throttle position sensors, vacuum leaks at plenum gaskets, and corroded wiring at the ECM connectors. Diagnosis takes 2-3 hours because problems are intermittent. TPS replacement is 1 hour, plenum gasket set is 4-5 hours. Many owners eventually swap to a carburetor or later TPI setup.

Estimated cost: $400-1,200

Symptoms: Water dripping on seats, headliner, or center console during rain, Musty smell, wet carpet in footwells, Rust bubbling at windshield pillars and floor pan seams, Fogged-up windows that won't clear

Fix: T-top weatherstripping hardens and shrinks after 15-20 years. Replacement seals (both panels and roof channels) take 3-4 hours to install properly with alignment adjustments. If water has been leaking for years, you're also looking at floor pan rust repair which can add 8-12 hours of metal work and welding.

Estimated cost: $500-900 seals only, $1,800-3,500 with floor pan repair

Typical onset: 90,000-150,000 mi

Symptoms: Gear oil dripping from pinion yoke or axle tubes, Whining or howling noise during deceleration, Clunking when shifting from drive to reverse, Low fluid level on dipstick (if equipped) or visible leaks on driveway

Fix: The 7.5-inch and 8.5-inch rear ends develop pinion seal leaks and side bearing failures. Pinion seal alone is 2-3 hours, but if you're there, smart money replaces side bearings too (add 4-6 hours for full teardown and setup with shims). Carrier bearings also wear with age, requiring carrier replacement.

Estimated cost: $600-1,400

Typical onset: 120,000-180,000 mi

Symptoms: Knocking or ticking noise from bottom end at idle, Low oil pressure at hot idle (under 10 psi), Metal flakes or glitter in oil during changes, Sudden loud knocking followed by seized engine

Fix: The small-block 305 and 2.8L V6 both suffer from bearing wear when oil changes were neglected. Rod knock requires engine R&R (8-10 hours) plus either bearing replacement in-car (add 6-8 hours machine shop time) or a full rebuild (16-20 hours shop labor). Most shops recommend a short block or junkyard replacement at this point due to age-related bore wear and ring lands.

Estimated cost: $2,800-5,500

Symptoms: Key won't turn or gets stuck in ignition, Steering wheel won't unlock even with key, Ignition turns but starter won't engage, Key can be removed while in accessory position

Fix: GM tilt columns of this era have weak ignition lock tumblers and worn lock plates. Replacement requires removing the steering wheel, lock plate compressor tool, and disabling the airbag (if equipped—most 1984s didn't have them). Labor is 2-3 hours. Rekey service adds another $50-80 if you want one key for doors and ignition.

Estimated cost: $350-600

Typical onset: 70,000-140,000 mi

Symptoms: No-start after sitting overnight, fires after multiple cranking attempts, Engine dies at idle after warming up, restarts after cooling, Fuel gauge reads incorrectly or bounces erratically, Whining noise from fuel tank area during driving

Fix: The in-tank electric fuel pump fails from corrosion and varnish buildup, especially if the car sits. Replacement requires dropping the tank (3-4 hours) and while you're in there, the sending unit usually needs replacement too because the float arm corrodes. Filter sock inside the tank clogs with sediment.

Estimated cost: $500-850