1971 CADILLAC ELDORADO

Typical onset: 80,000-140,000 mi

Symptoms: Slipping between gears, especially 2nd to 3rd, Delayed engagement when shifting to Drive or Reverse, Whining or grinding noises from under the car, Burnt transmission fluid smell, dark or metallic fluid

Fix: The TH425 is a transaxle-style transmission combining gearbox and differential. Rebuild requires 18-24 hours labor due to front-wheel-drive configuration and tight engine bay. Often includes new clutch packs, bands, seals, and torque converter. Transmission oil cooler lines frequently corrode and should be replaced simultaneously to prevent future contamination.

Estimated cost: $3,200-5,800

Typical onset: 100,000-150,000 mi

Symptoms: Excessive blue smoke on startup or acceleration, Oil consumption of 1+ quart per 500-800 miles, Loss of compression and power, Fouled spark plugs, particularly rear cylinders

Fix: The 500 was last year before emissions strangling but still suffers ring land carbon buildup and bore glazing with age. Full rebuild involves engine removal (12-16 hours), bore honing or sleeving, new rings, bearings, gaskets, timing set. Many shops recommend addressing valve guides and seats while in. Engine R&R is complicated by FWD layout and accessories.

Estimated cost: $4,500-7,500

Symptoms: Transmission fluid puddles under front of vehicle, Rapid fluid loss leading to slipping or no movement, Visible corrosion or seepage along steel cooler lines, Sudden loss of all gears after hearing pop or snap

Fix: Steel cooler lines rust through from road salt and age, often at bends or mounting points. Failure dumps all ATF within minutes. Replacement requires 3-5 hours including custom bending or pre-fabricated lines. Must flush cooler and inspect radiator-mounted cooler core for contamination. Always replace both lines and rubber hoses as preventive measure.

Estimated cost: $450-850

Typical onset: 60,000-100,000 mi

Symptoms: Clunking when shifting into gear or heavy acceleration, Excessive engine movement visible when revving, Vibration through steering wheel and floorboards, Interference between engine and firewall or fender aprons

Fix: The massive 500ci engine combined with torque reaction stress destroys rubber mounts. Front mounts are accessible but require engine support (4-6 hours for both sides). Transmission mount often needs simultaneous replacement as symptoms overlap. Old mounts can allow engine to shift enough to stress exhaust, accessory belts, and radiator hoses.

Estimated cost: $550-950

Symptoms: Hesitation or stumble on acceleration from idle, Fuel leaking from carburetor base or vent tubes, Hard starting when hot, flooding when cold, Raw fuel smell in engine bay after shutdown

Fix: Rochester Quadrajet on these develops worn accelerator pump diaphragms and stuck or misadjusted floats from ethanol fuel. Rebuild takes 4-6 hours including removal, cleaning, new kit, and tuning. Original cores are valuable; avoid cheap offshore replacements. Proper float height critical to prevent flooding or lean stumble.

Estimated cost: $450-750

Typical onset: 120,000-180,000 mi

Symptoms: Deep knocking sound from bottom of engine, worse under load, Low oil pressure at idle when hot (below 10 psi), Metallic debris in oil filter and pan, Vibration through entire vehicle at specific RPM ranges

Fix: Bearing failure typically from insufficient oil changes or running low on oil. Requires complete engine disassembly with crank polishing or replacement (20-30 hours total labor). Often discovered during ring job inspection. Crankshafts can be saved if journals are within spec for 0.010" or 0.020" undersize bearings. Connecting rod bearings usually need replacement simultaneously.

Estimated cost: $5,500-9,000