1976 CADILLAC CALAIS

Typical onset: 50,000-90,000 mi or after extended storage

Symptoms: Hard starting when cold, excessive cranking, Rough idle, stalling at stop lights, Black smoke from exhaust, poor fuel economy below 8 mpg, Hesitation on acceleration

Fix: The 1976 models use primitive emissions controls with lean calibrations. Carburetors need full rebuild with modern ethanol-resistant kits, accelerator pumps fail frequently. Fuel filters clog from tank sediment—expect to drop the tank and clean it if the car sat. Budget 4-6 hours for carb rebuild, 2-3 hours for fuel system flush and filter replacement.

Estimated cost: $600-1,200

Typical onset: 70,000-120,000 mi

Symptoms: Transmission fluid pooling under car, pink/red stains on driveway, Slipping between gears, delayed engagement into Drive, Overheating on highway runs, burnt smell, Low fluid level on dipstick

Fix: The THM 400 is bulletproof internally, but external seals and cooler lines rot out. Transmission oil cooler lines rust through where they pass the frame, spraying fluid onto exhaust. Front pump seal and pan gasket leaks are epidemic. Cooler line replacement takes 2 hours, pan gasket and filter service 1.5 hours. If fluid's been low long enough, internal clutches burn—full rebuild runs 12-16 hours.

Estimated cost: $300-800 for seals/lines, $2,200-3,500 for full rebuild

Typical onset: 60,000-100,000 mi or 40+ years age

Symptoms: Loud clunk when shifting from Park to Drive or Reverse, Excessive vibration at idle, felt through steering wheel and floorboards, Engine visibly rocking side-to-side during acceleration, Transmission tunnel heat and noise increased

Fix: Rubber mounts disintegrate from age and oil exposure. The transmission mount is especially prone to failure—it sits right above the exhaust crossover. Engine mounts collapse, letting the big-block sag onto the frame. Replacement is straightforward but requires lifting the drivetrain with a jack. Budget 3-4 hours for transmission mount, 4-5 hours for both engine mounts.

Estimated cost: $400-700

Typical onset: 80,000-150,000 mi or after overheating

Symptoms: Coolant leaking externally at front or rear of intake manifold, White smoke from exhaust, sweet smell, Overheating, loss of coolant with no visible external leaks, Oil looks milky or chocolate-colored on dipstick, Rough idle, misfiring

Fix: The 472/500/425 engine family has notorious intake manifold gasket issues—these gaskets fail and allow coolant into the valley or oil passages. Head gaskets go if the car overheats (common with 50-year-old radiators). Intake manifold gasket job takes 6-8 hours, head gaskets on both banks run 14-18 hours due to A/C and power steering removal. If heads are warped, add machining costs.

Estimated cost: $1,200-1,800 intake gaskets, $2,800-4,500 head gaskets both sides

Typical onset: 120,000-180,000 mi

Symptoms: Blue smoke on startup and during acceleration, Burning through a quart of oil every 500-800 miles, Fouled spark plugs, misfires, Low compression on multiple cylinders, Oil coating on exhaust tips

Fix: These engines run low-tension rings that wear out, especially if oil changes were skipped. Piston ring replacement requires full engine disassembly—you're looking at 20-25 hours labor. Most shops recommend a full rebuild at this point since you're already in there: new bearings, cam inspection, valve job. If the block needs boring or the crank needs turning, add machine shop time.

Estimated cost: $3,500-6,000 in-chassis rebuild, $5,000-8,500 with machine work

Typical onset: 150,000+ mi or severe neglect

Symptoms: Deep knocking sound from bottom of engine, worsens with RPM, Low oil pressure at idle, flickering oil light, Metallic rattling that disappears when spark plug wire is pulled on affected cylinder (rod knock), Metal shavings in oil, glitter on drain plug magnet

Fix: Main and rod bearing failures mean the crank is damaged. Crankshaft R&R requires complete engine disassembly—you're pulling the engine (8-10 hours), tearing it down, sending the crank out for machining (grinding undersize), then reassembly with oversized bearings. Total job runs 25-30 hours. Most owners opt for a reman long block or salvage engine swap at this point.

Estimated cost: $4,500-7,500 crank grind and rebuild, $3,000-5,000 reman long block swap