1984 CHEVROLET C20

Typical onset: 80,000-150,000 mi

Symptoms: Clunk when shifting from park to drive or reverse, Excessive drivetrain movement felt through cab floor, Vibration at idle that changes when shifting into gear, Visible cracking or separation of rubber mount body

Fix: Replace transmission mount and crossmember bushings while underneath — typical 1.5-2 hours with basic hand tools. The rubber deteriorates from heat, oil contamination, and constant torque cycling. Often find the mount completely separated when diagnosis begins with a clunk complaint.

Estimated cost: $150-350

Typical onset: 120,000-180,000 mi

Symptoms: Slipping between gears, especially 2nd to 3rd on 700R4, Delayed engagement when cold, Burnt transmission fluid smell and dark red or brown fluid color, Hard shifts or no upshift into overdrive on 700R4 models

Fix: Transmission oil cooler clogs or external cooler lines leak, causing overheating and clutch pack failure. Rebuild runs 12-16 hours labor plus 8-10 hours for R&R. Many shops recommend adding aftermarket cooler during rebuild. The 700R4 overdrive units are more prone to issues than the bulletproof TH400.

Estimated cost: $1,800-3,200

Typical onset: 150,000-220,000 mi

Symptoms: Low oil pressure at idle when hot (below 10 psi), Knocking or rattling from lower engine block, Metal flakes or excessive bearing material in oil, Excessive blowby and crankcase pressure

Fix: Main bearings and rod bearings wear from inadequate oil change intervals or running conventional oil in high-load applications. Full short block replacement or in-frame rebuild required — engine R&R is 10-14 hours, machine work and reassembly adds another 18-24 hours. Many owners opt for long block replacement or remanufactured short block to save labor.

Estimated cost: $3,500-6,500

Typical onset: 120,000-180,000 mi

Symptoms: Hard starting or extended cranking, especially when cold, Loss of power and black smoke under load, Erratic idle and fuel knock at operating temperature, Diesel fuel leak from pump housing

Fix: Stanadyne DB2 mechanical injection pump wears internally, losing fuel delivery precision. Replacement or rebuild required — 4-6 hours labor for pump R&R plus injection timing setup. These pumps are sensitive to fuel contamination, so always replace fuel filter and check tank for debris during repair.

Estimated cost: $1,200-2,200

Typical onset: 140,000-200,000 mi

Symptoms: Blue smoke on startup that clears after warmup, Oil consumption over 1 quart per 1,000 miles, Reduced compression and sluggish acceleration, Carbon buildup visible around exhaust manifold

Fix: The 292 six is incredibly durable but eventually needs piston rings and valve work. Many owners do in-frame ring job without full removal — 8-12 hours. However, if valve guides are worn, cylinder head work adds complexity. Full rebuild with engine out runs 20-26 hours total.

Estimated cost: $1,500-3,800

Symptoms: Rough idle or stalling after sitting for weeks, Hesitation under acceleration, Hard starting that improves after replacing fuel filter, Visible rust or debris when dropping fuel tank

Fix: Steel fuel tanks rust internally over decades, especially in humid climates or from condensation in partially-filled tanks. Fuel filter plugs frequently on neglected trucks. Replace filter every 15k-20k miles preventively — 0.5 hour job. If tank is heavily contaminated, drop and clean or replace tank — 3-4 hours labor.

Estimated cost: $25-80 for filter, $400-800 for tank replacement

Symptoms: Rough idle and stalling at stop signs, Black smoke and poor fuel economy, Gasoline smell from engine bay due to float bowl leaks, Hard cold starting requiring excessive pumping

Fix: Rochester Quadrajet and other OE carburetors develop internal wear, stuck floats, and deteriorated gaskets after 30-40 years. Rebuild kits run $80-150, labor is 2-3 hours for competent carburetor tech. Many owners convert to Edelbrock or Holley for reliability, adding another $300-500 in parts.

Estimated cost: $250-650 for rebuild, $500-900 for replacement