1979 CHEVROLET C30

Typical onset: 80,000-150,000 mi

Symptoms: Clunking when shifting from park to drive, Excessive driveline vibration under throttle, Visible transmission sag when inspected from underneath, Transmission shifting harshly

Fix: The rubber mount tears and the crossmember cracks from heavy loads and frame flex. Replacement involves supporting the transmission, dropping the crossmember, and installing new mount and hardware. 2-3 hours labor. Often find the crossmember itself cracked and needing replacement, especially on dual-rear-wheel models.

Estimated cost: $250-500

Typical onset: 150,000-250,000 mi

Symptoms: Heavy knocking on startup that quiets when warm, Visible metal particles in oil, Oil pressure dropping below 10 psi at idle when hot, Rod knock audible under load

Fix: These engines ran hard pulling loads and often saw deferred maintenance. Main and rod bearings wear, sometimes scoring the crank. Full teardown required - yank the engine, hot-tank the block, measure everything, regrind crank if scored, new bearings, rings, timing set, gaskets, seals. Full rebuild 18-25 hours, short block replacement 12-16 hours if you find a good core.

Estimated cost: $3,500-6,500

Symptoms: Hard starting or no-start after sitting, Rough idle and stumbling acceleration, Fuel leaking from carburetor base or accelerator pump, Black smoke and flooding

Fix: Trucks parked for years develop varnished fuel in the tank, lines, and carburetor passages. Rochester Quadrajet or small-bore carbs need full rebuild kits, ultrasonic cleaning of castings, new fuel filter, sometimes tank drop and cleaning or replacement. Figure 4-6 hours for carb rebuild, fuel system flush, and filter replacement. Add 3-4 hours if tank needs service.

Estimated cost: $400-900

Symptoms: Visible rust perforation on frame rails behind cab, Soft or flaking metal around body mount locations, Cracking paint and scale buildup on frame, Transmission or transfer case mounts pulling through weakened metal

Fix: Salt-belt and work-truck life kills frames. Rust concentrates at body mounts, behind cab corners, and transmission crossmember mounting points. Serious cases need frame section replacement or boxing/plating - 12-20 hours depending on extent. Minor surface rust gets wire-wheeled and painted. Structural rust is a truck-killer - inspect thoroughly before buying.

Estimated cost: $1,200-4,000

Typical onset: 100,000-180,000 mi

Symptoms: Excessive play at steering wheel (more than 2 inches), Wandering on highway requiring constant correction, Clunking felt through steering wheel over bumps, Fluid leaking from gearbox sector shaft seal

Fix: Saginaw manual steering boxes wear internally, developing slop in the sector shaft and worm gear. Adjustment helps temporarily but most need rebuilding or replacement. Rebuilt box swap takes 3-4 hours including alignment. New boxes are expensive, rebuilt units are the budget play. Power steering models leak at the sector seal and need periodic box rebuilds.

Estimated cost: $450-850

Typical onset: 120,000-200,000 mi

Symptoms: Gear oil dripping from axle tube ends, Howling or grinding noise from rear end under load, Axle shaft end play detectable by hand, Brake contamination from leaking seal

Fix: Heavy loads and age kill the outer axle seals and wheel bearings on these full-float axles. Pull the axle shafts, replace seals, bearings, and races. Both sides typically done together. 4-5 hours labor per axle. If the howl is coming from the carrier, you're looking at ring and pinion or carrier bearing work - add $800-1500 in parts and 6-8 more hours.

Estimated cost: $600-1,000

Symptoms: Cannot switch between tanks using dash switch, Fuel starvation when one tank reads full, Fuel smell in cab from vapor leaks at selector valve, Running out of fuel despite gauge showing quarter tank

Fix: The mechanical fuel selector valve mounted on frame rail corrodes internally and fails to switch or develops vacuum leaks. Replacement involves dropping fuel lines, installing new valve, bleeding system. 2-3 hours. Sometimes the dash switch fails instead - quick electrical diagnosis saves throwing parts at it.

Estimated cost: $200-400