1976 CADILLAC DEVILLE

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

Symptoms: rough idle and stalling, black smoke from exhaust, flooding or hard starting when warm, poor fuel economy even by 1976 standards (8-10 mpg), hesitation on acceleration

Fix: Rochester Quadrajet carbs on these engines need full rebuilds or replacement, often combined with new intake manifold gaskets which harden and crack. Expect 4-6 hours labor for carb rebuild and intake gasket replacement together. Many shops now replace with remanufactured units rather than rebuild in-house.

Estimated cost: $650-1,200

Typical onset: 80,000-140,000 mi

Symptoms: transmission fluid leaking from cooler lines at radiator, pink milkshake in radiator (coolant-ATF mixing), slipping between gears especially 1-2 shift, delayed engagement when shifting to Drive or Reverse, metal shavings in pan during fluid change

Fix: Cooler lines rust through where they pass the frame, and internal radiator separator fails causing fluid contamination. Cooler line replacement is 2-3 hours. If coolant entered transmission, you're looking at full rebuild or replacement—8-12 hours labor plus reman unit. These THM400s are stout but this crossover contamination kills them.

Estimated cost: $300-600 for lines only, $2,800-4,200 for full transmission rebuild

Typical onset: 120,000+ mi or on neglected oil change intervals

Symptoms: heavy knocking from bottom end especially when cold, oil pressure dropping below 10 psi at idle when hot, metallic debris in oil filter and pan, vibration through entire vehicle at idle

Fix: The 500ci V8 is known for main bearing failures, particularly #3 and #5, especially if run low on oil or with extended intervals. This requires complete engine disassembly—crankshaft R&R, machining, and bearing replacement. Many shops recommend short block replacement or full engine rebuild at this point. 18-25 hours labor, plus machine work and parts. Often more cost-effective to source a running take-out engine.

Estimated cost: $3,500-6,500 for in-chassis rebuild, $2,500-4,000 for used engine swap

Symptoms: fuel smell in garage or cabin, hard starting after sitting overnight, stalling shortly after startup, visible fuel weeping from sending unit or lines, runs fine then suddenly dies and won't restart

Fix: These cars were never designed for ethanol fuel. Rubber fuel lines, tank sending unit gaskets, and fuel pump diaphragms deteriorate. In-tank sock filters disintegrate. Complete fuel system refresh includes tank drop and cleaning, new sending unit, all rubber lines, fuel filter, and fuel pump. Tank removal and reinstall alone is 3-4 hours on these big cars, full system refresh is 6-9 hours.

Estimated cost: $800-1,500

Typical onset: 100,000+ mi

Symptoms: blue smoke on startup or deceleration, using 1+ quart every 500-800 miles, fouled spark plugs especially rear cylinders, oil in air cleaner, loss of power on highway grades

Fix: Ring wear is common on neglected engines or those that sat for years. Top-end rebuild (rings, hone, valve job) requires engine removal on these—cylinder heads are massive and access is terrible in-chassis. 20-28 hours labor. However, if rings are gone, bearings usually aren't far behind, so many techs push for complete engine rebuild or long block replacement instead of chasing it in stages.

Estimated cost: $2,800-4,500 for top-end rebuild, $4,500-7,000 for complete rebuild

Typical onset: 60,000-100,000 mi

Symptoms: clunk when shifting from Park to Drive or Reverse, vibration at idle in gear that disappears in Park/Neutral, visible sag or tears in rubber mount, excessive driveshaft movement when rocking car

Fix: The rubber transmission mount deteriorates from age and heat. Simple replacement job—1.5-2 hours with car on lift. Often combined with checking engine mounts which also fail. This is routine maintenance on survivors but gets ignored because the car still drives.

Estimated cost: $180-350