1973 BUICK CENTURION

Typical onset: 70,000-120,000 mi

Symptoms: Burnt transmission fluid smell, Delayed or harsh shifts when hot, Slipping in 2nd or 3rd gear after highway driving, Pink milky fluid if cooler leaks into radiator

Fix: The factory transmission oil cooler in the radiator tank fails or the external lines corrode through. If coolant mixes with ATF, you're looking at a full rebuild. Prevention means adding an external cooler and replacing the in-radiator unit. Rebuild takes 8-12 hours including R&R and valve body work.

Estimated cost: $1,800-3,200

Typical onset: 80,000-150,000 mi

Symptoms: Blue smoke on acceleration or deceleration, Burning through a quart every 500-800 miles, Fouled spark plugs on cylinders 2, 4, 6, 8, Low compression readings below 120 psi

Fix: The 455's soft piston rings wear quickly, especially if overheated even once. Proper fix is a ring job (12-16 hours) or full rebuild if cylinder walls are scored. Many shade-tree guys try high-mileage oil and keep topping off, but that's just delaying the inevitable.

Estimated cost: $2,200-4,800

Typical onset: 100,000-180,000 mi

Symptoms: Deep knocking sound at idle that quiets with RPM, Low oil pressure below 10 psi hot at idle, Metallic debris in oil filter, Vibration through whole chassis

Fix: Both the 350 and 455 can develop main bearing wear if oil changes were neglected or if the engine ran hot. Requires pulling the crank, checking journals for out-of-round, and installing oversize bearings. Full job is 16-20 hours because you're essentially doing a short block rebuild.

Estimated cost: $3,500-5,500

Typical onset: 60,000-100,000 mi

Symptoms: Clunk when shifting from Park to Drive or Reverse, Excessive vibration at idle in gear, Visible sagging of transmission tailshaft, Driveline shudder on acceleration

Fix: The rubber crossmember mount deteriorates from heat and age. It's a 1.5-2 hour job with the car on a lift—drop the crossmember, swap the mount, reinstall. Dead simple but often ignored until it tears completely.

Estimated cost: $180-350

Symptoms: Hard starting when hot, Sputtering or stalling under load after sitting, Fuel pump working but weak delivery, Engine dies after 15-20 minutes of driving

Fix: Old gas turns to varnish in the tank and lines, especially if the car sat for years. Filter clogs quickly even after tank cleaning. You'll need to drop and clean or replace the tank, blow out all lines, replace filter and pump sock. Budget 4-6 hours if the tank comes out.

Estimated cost: $400-900

Symptoms: Raw gas smell in engine bay, Black smoke and rough idle, Gas dripping from carb base or accelerator pump, Hard starting with repeated cranking needed

Fix: The Rochester Quadrajet carbs use rubber-tipped needle valves that harden with age and no longer seal. Float levels go out of spec. A proper rebuild with new kit and float adjustment takes 3-4 hours if you know these carbs; double that if you don't. Many shops now just swap in a reman unit.

Estimated cost: $350-750