1978 CADILLAC DEVILLE

Typical onset: 60,000-120,000 mi

Symptoms: rough idle and stalling at stops, hesitation on acceleration, black smoke from exhaust, poor fuel economy even by 1970s standards, check engine light or Service Engine Soon light

Fix: The Quadrajet carburetor requires rebuild or replacement, and the maze of vacuum hoses, EGR valves, and early computer controls fail regularly. Expect 4-6 hours for carburetor rebuild, additional 2-3 hours for emission control diagnostics and vacuum line replacement. Many shops now convert to aftermarket EFI for reliability.

Estimated cost: $800-1,800

Typical onset: 80,000-150,000 mi

Symptoms: severe clunk when shifting from park to drive, visible transmission sag when inspecting underneath, vibration at idle in gear, difficulty shifting or grinding

Fix: The rubber transmission mount deteriorates and the transmission literally drops, stressing the driveline and sometimes cracking the transmission case or damaging the shifter linkage. Requires transmission support, mount replacement, and inspection for secondary damage. 3-5 hours labor depending on access and complications.

Estimated cost: $400-900

Symptoms: transmission fluid leak at radiator or along frame rails, transmission overheating and slipping, pink or red fluid puddles under car, low transmission fluid on dipstick

Fix: The steel transmission cooler lines rust through at the frame or fittings, dumping ATF rapidly. If coolant mixes with transmission fluid at the radiator cooler, the transmission is often destroyed. Replacement requires 2-3 hours for lines, but if internal radiator leak occurred, add transmission rebuild (12-16 hours). Inspect radiator cooler integrity during every service.

Estimated cost: $300-600 for lines only; $2,500-4,500 if transmission contaminated

Typical onset: 80,000-140,000 mi

Symptoms: engine dies after running 15-30 minutes, hard starting when hot, sputtering under load, fuel smell in cabin or trunk area

Fix: Fuel pump (mechanical on 425ci, in-tank electric on some 403ci), fuel filter, and rubber fuel lines harden and fail. The fuel pump pushrod can wear the block eccentric. Plan on fuel pump replacement, all rubber lines, filter, and tank cleaning if sitting. 4-6 hours for complete fuel system service including dropping tank.

Estimated cost: $600-1,200

Typical onset: 120,000-180,000 mi

Symptoms: excessive blue smoke on startup and acceleration, oil consumption over 1 quart per 500 miles, loss of compression and power, fouled spark plugs

Fix: The 425ci and 403ci engines develop ring wear and cylinder scoring, especially if overheated or run low on oil. Owners often face the rebuild-or-replace decision. Expect 24-32 hours for complete engine rebuild including machine work, or 16-20 hours for long block swap. Parts availability for 403ci Olds engine is better than 425ci Cadillac-specific parts.

Estimated cost: $4,500-8,000

Typical onset: 70,000-110,000 mi

Symptoms: soft or spongy brake pedal, pedal sinks to floor when held, brake fluid leak at firewall, hard pedal with poor braking power

Fix: The dual master cylinder and vacuum booster degrade, often leaving only one brake circuit functional. Given the car's 5,000+ lb weight, this is dangerous. Replacement requires 3-4 hours including bleeding the system. Parts are still available but shop carefully for quality.

Estimated cost: $500-900

Typical onset: 80,000-130,000 mi

Symptoms: clunking over bumps, wandering steering and poor tracking, uneven tire wear, steering wheel shimmy at highway speed

Fix: The heavy front end eats ball joints, particularly uppers, and the steering idler arm wears out. Requires front-end disassembly, replacement of worn components, and alignment. 5-7 hours for upper and lower ball joints plus idler arm. This isn't unique to DeVille but the weight accelerates wear.

Estimated cost: $800-1,400