1971 GMC C2500

Typical onset: 80,000-150,000 mi

Symptoms: Hard starting when warm, Rough idle with ignition timing properly set, Backfiring through carburetor, Check timing and find it's retarded 10+ degrees despite distributor being correct

Fix: Replace timing chain, gears, and tensioner. Nylon-toothed cam gears deteriorate and chains stretch. Requires front cover removal, harmonic balancer puller, and new timing set. 4-6 hours labor for experienced tech, more if you hit stuck bolts or need to pull radiator.

Estimated cost: $400-800

Symptoms: Excessive play at steering wheel (more than 2 inches), Wandering on highway requiring constant correction, Clunking when turning from center, Truck pulls randomly left or right

Fix: Saginaw manual steering boxes wear internally and adjustment only helps temporarily. Pitman and idler arms wear badly. Full steering rebuild includes gearbox replacement or professional rebuild, pitman arm, idler arm, tie rod ends, and alignment. 5-8 hours labor for complete job.

Estimated cost: $800-1,400

Symptoms: Stalling when hot, restarts after cooling, Loss of power on hot days or long uphill pulls, Engine starves for fuel then recovers, Won't restart until engine cools 20-30 minutes

Fix: Mechanical fuel pumps fail from diaphragm rupture or weak springs. Vapor lock common due to fuel line routing near exhaust. Replace pump (1 hour), reroute fuel lines away from heat sources, consider adding return line and insulating lines. Electric fuel pump conversion solves it permanently.

Estimated cost: $150-450

Symptoms: Soft or spongy brake pedal that slowly sinks to floor, Fluid leaking at rear wheel backing plates, Visible drips from master cylinder at firewall, Brake warning light illuminates (if equipped)

Fix: Single-circuit master cylinders leak internally, and rear wheel cylinders seize or leak. Safety critical. Replace master cylinder (2 hours), rebuild or replace wheel cylinders (1.5 hours per axle), flush system, bleed thoroughly. Consider dual-reservoir master upgrade for safety.

Estimated cost: $350-700

Typical onset: 100,000+ mi

Symptoms: Transmission fluid puddle under tailshaft, Slipping on acceleration after sitting, White smoke from exhaust if modulator diaphragm fails, Low fluid level despite no visible external leak

Fix: Tail housing seal leaks from age and yoke wear. Vacuum modulator diaphragms rupture, sucking ATF into intake. Tail seal replacement requires driveshaft removal and sometimes transmission drop (2-4 hours). Modulator is 0.5 hour and cheap. Check yoke for grooves.

Estimated cost: $200-500

Symptoms: Cab visibly sagging or tilted, Door alignment issues that worsen over time, Cracks in cab corners near windshield, Visible rust perforation in cab floor or rocker panels

Fix: Cab mounts disintegrate from age and salt exposure. Frame rust behind cab and in crossmembers compromises structural integrity. Cab mount replacement requires lifting cab (8-12 hours). Frame rust may require sectional replacement or retiring the truck. Inspect thoroughly before purchase.

Estimated cost: $800-2,500

Symptoms: Ammeter shows discharge at idle, Battery constantly needs charging, Dim lights at idle that brighten with RPM, Battery light on (later models)

Fix: Early '71s may have generators; later models have alternators. Voltage regulators fail externally mounted units. Generator rebuild or alternator replacement straightforward. Upgrade to higher-amp alternator recommended for reliability. 1-2 hours labor.

Estimated cost: $200-400