1972 AUDI 100

Typical onset: 80,000-150,000 mi

Symptoms: Heavy rod knock or main bearing knock on cold start, Low oil pressure at idle when warm, Metal shavings in oil filter, Blue smoke from worn rings compounding the problem

Fix: These engines rarely die from top-end issues—it's the bottom end that goes. Main bearings wear oval, rods get loose, and ring wear drops compression. Requires complete engine rebuild with new main/rod bearings, honing cylinders, and new rings at minimum. Plan 18-24 labor hours for a proper rebuild or 12-16 hours for engine R&R with a used/rebuilt unit. Most survivors need this work now regardless of mileage due to age and oil degradation over decades.

Estimated cost: $2,800-5,500

Symptoms: Transmission fluid leaking from hard lines near radiator, Red fluid puddles under front of car, Burnt transmission smell if fluid level drops significantly, Slipping gears under load

Fix: The metal cooler lines rot out from 50+ years of road salt and moisture. Lines crack at bends or corrode through completely. Requires fabricating or sourcing replacement hard lines and flushing the system. If caught early, 3-4 hours labor. If the transmission ran low on fluid, expect internal damage requiring rebuild.

Estimated cost: $350-800

Symptoms: Excessive clunking when shifting from park to drive, Vibration through shifter at idle, Transmission sag visible from underneath, Driveline shudder on acceleration

Fix: Rubber mounts deteriorate completely after 50 years, allowing the transmission to drop and create driveline angles that accelerate U-joint wear. Replacement requires supporting the transmission, unbolting old mounts, and installing new or fabricated bushings. Factory parts are extinct—expect polyurethane replacements or machine shop fabrication. 2-3 hours labor.

Estimated cost: $250-600

Symptoms: Hard starting after sitting, Rough idle and hesitation, Stalling at operating temperature, Fuel odor from degraded rubber lines

Fix: Old fuel leaves varnish throughout the system. Carburetors gum up, fuel filters clog solid, and rubber fuel lines turn to mush internally. Requires complete fuel system service: carburetor rebuild or replacement, new fuel filter, replacement of all rubber fuel lines, and tank cleaning or replacement. Plan 6-8 hours for thorough work.

Estimated cost: $600-1,400

Typical onset: 100,000+ mi

Symptoms: Clunking when engaging clutch, Excessive crankshaft movement visible at pulley, Oil leaks from front and rear main seals, Metallic grinding noise during clutch operation

Fix: The thrust bearing wears and allows excessive crankshaft fore-aft movement, which destroys main seals and can damage the block. Requires full engine disassembly to replace thrust washers and check crank journal condition. Often discovered during bottom-end rebuilds. Add 4-6 hours to rebuild time if addressed separately.

Estimated cost: $1,200-2,200

Symptoms: Overheating in traffic or at highway speeds, Coolant leaks from water pump, hoses, or radiator, Rusty coolant color, Heater produces little heat

Fix: Original radiators rot internally, water pumps seize, and rubber hoses crack. The entire cooling system needs replacement as a preventive measure on any survivor. New radiator, water pump, thermostat, all hoses, and flush. Heater cores often leak internally requiring dash removal. 5-7 hours for complete system overhaul.

Estimated cost: $800-1,600