1971 CADILLAC CALAIS

Typical onset: 80,000-120,000 mi

Symptoms: Transmission slipping in 2nd or 3rd gear under load, Burnt ATF smell or dark brown/black fluid, Delayed engagement when shifting from Park to Drive, Cooler lines leaking at radiator or transmission fittings

Fix: The TH400 transmission oil cooler integrated into the radiator corrodes and fails, contaminating coolant with ATF or vice-versa. External cooler lines rot out. Full rebuild typically requires 12-16 hours labor plus removal/replacement of cooler lines and often the radiator. Add external aux cooler during rebuild to prevent repeat failure.

Estimated cost: $2,800-4,200

Symptoms: Hard starting when hot or after sitting, Fuel smell in garage or under car, Engine stumbling or dying at idle, Visible cracking on rubber fuel hoses near tank and pump

Fix: 50+ year-old rubber fuel lines from tank to pump and pump to carb become brittle and leak or collapse internally. The sock filter in the tank clogs with rust and varnish. Requires dropping the tank (3-4 hours), replacing all rubber lines, and installing new sending unit/sock. Ethanol fuel accelerates degradation.

Estimated cost: $600-1,200

Typical onset: 100,000-150,000 mi

Symptoms: Deep knocking noise on cold start that fades slightly when warm, Low oil pressure at idle (under 10 psi hot), Metallic particles visible on drain plug magnet, Gradual loss of power and increased oil consumption

Fix: The massive 472 has generous bearing clearances from the factory; when they wear beyond spec, oil pressure drops and knocking begins. Requires full engine teardown and rebuild with new bearings, often pistons/rings due to ridge wear. Some shops quote short-block replacement instead (18-24 hours labor). Crankshaft may need machining if bearings spun.

Estimated cost: $4,500-7,500

Typical onset: 60,000-100,000 mi

Symptoms: Clunk when shifting from Reverse to Drive, Excessive drivetrain movement visible when accelerating hard, Vibration in floorboard at idle in gear, Visible sagging or cracking of rubber mount under transmission

Fix: The rubber transmission mount deteriorates from age, heat, and fluid exposure. Allows excessive movement and stress on driveshaft U-joints. Replacement requires supporting transmission on jack, unbolting crossmember (2-3 hours). Often done with U-joint service simultaneously.

Estimated cost: $250-450

Symptoms: Rough idle with occasional stalling in gear, Black smoke on acceleration or overly rich smell, High idle speed that won't adjust down, Bog or hesitation when accelerating from stop

Fix: The Rochester Quadrajet accumulates varnish in passages and develops vacuum leaks at base gasket or secondary throttle plates. Rebuild kit and cleaning takes 4-6 hours for proper bench work; includes replacing accelerator pump, float, and all gaskets. Many shops outsource to carb specialists.

Estimated cost: $400-800

Typical onset: 120,000+ mi

Symptoms: Blue smoke on startup or deceleration, Oil consumption exceeding 1 quart per 500 miles, Low compression on multiple cylinders, Excessive crankcase pressure pushing oil past valve covers

Fix: Rings lose tension and cylinder walls develop ridges at the top of piston travel. Requires bore inspection and typically a full rebuild with new pistons and rings, plus cylinder honing or boring (22-28 hours labor for long-block). Some owners opt for used replacement engines instead.

Estimated cost: $5,000-8,500