1980 CHEVROLET C20

Typical onset: 60,000-100,000 mi

Symptoms: Clunking on acceleration or deceleration, Excessive drivetrain vibration, Visible transmission sag or shifter misalignment

Fix: Rubber mount deteriorates from heat and age, causing the transmission tail to drop. Replacement requires transmission jack support, typically 1.5-2 hours labor. Often find the crossmember cracked too, adding cost.

Estimated cost: $150-350

Symptoms: Hard starting when hot, Stumbling off idle or hesitation, Black smoke and poor fuel economy, Leaking fuel from float bowl or accelerator pump

Fix: The computer-controlled Quadrajet with its maze of vacuum lines and feedback solenoids is this truck's Achilles heel. Most need full rebuild with ethanol-resistant kit at 40+ years old. Proper rebuild takes 3-4 hours with tuning. Many owners swap to Holley or Edelbrock and delete emissions, which is cleaner but not emissions-legal.

Estimated cost: $400-800

Typical onset: 150,000-250,000 mi

Symptoms: Deep knocking from bottom end, worse when cold, Low oil pressure at idle when hot, Metallic debris in oil filter

Fix: These engines were workhorses, and many survivors have serious miles. Main bearings fail first, scoring the crank. Requires engine removal, machine work on crank (turn or replace), line bore check on block. 20-25 hours labor for proper rebuild. Many opt for reman long block swap instead at 12-15 hours labor.

Estimated cost: $3,500-6,500

Typical onset: 120,000-180,000 mi

Symptoms: Blue smoke on startup or deceleration, Burning 1+ quart per 500-1000 miles, Fouled spark plugs, Loss of compression on leak-down test

Fix: The 292 I6 especially suffers from worn rings in the upper cylinders. In-frame ring job requires head removal, ridge reaming, honing if cylinders are still round. 12-16 hours labor. If cylinders are tapered beyond spec, needs full rebuild or short block. Many just keep adding oil if it still runs strong.

Estimated cost: $1,800-3,200

Typical onset: 150,000-200,000 mi

Symptoms: Slipping in 2nd or 3rd gear under load, Delayed or harsh engagement into drive, No 3rd gear or stuck in 2nd, Metal shavings in pan

Fix: The TH400 is bulletproof when maintained, but these trucks often towed heavy without coolers or fluid changes. Clutch packs and pump wear out. Full rebuild with converter is 8-12 hours labor. Most also replace the weak cooler lines and add external cooler at same time.

Estimated cost: $1,800-2,800

Symptoms: Stalling or rough running after sitting, Fuel starvation under load, Repeated fuel filter clogging, Visible rust in fuel filter or carburetor bowl

Fix: Original steel fuel tanks rust from inside out after decades, especially if stored outside. Particulates clog sock filter, inline filter, and carburetor jets. Proper fix is tank removal, cleaning or replacement, new sending unit, all fuel lines flushed. 4-6 hours labor. Cheap fix is inline filter every oil change and keep tank full.

Estimated cost: $600-1,200