1971 GMC K1500

Symptoms: Sagging cab corners, Visible rust-through on frame rails behind cab, Body mounts crumbling, Doors won't close properly due to body shift

Fix: Frame sections may need patching or replacement if compromised near spring hangers or steering box mount. Cab mount replacement takes 8-12 hours with body lift and requires new bushings. Full frame replacement or extensive welding is a 30+ hour job.

Estimated cost: $800-3,500 for cab mounts; $4,000-8,000+ for frame repair

Typical onset: 80,000-150,000 mi

Symptoms: Rattling on cold start that disappears when warm, Hard starting or backfiring through carburetor, Loss of power at higher RPM, Check timing and it's retarded several degrees

Fix: Replace timing chain, gears, and preferably the oil pump drive gear while you're in there. Figure 4-6 hours for a straightforward R&R with new gaskets and oil change. Use a double-roller chain kit if keeping long-term.

Estimated cost: $400-900

Typical onset: 100,000+ mi

Symptoms: Grinding or growling from transfer case, Fluid leaking from front output seal, Won't engage or disengage 4WD cleanly, Vibration in 2WD from worn differential carrier

Fix: The NP203 full-time case has a center differential that wears and causes binding. Seal replacement is 2-3 hours. Internal rebuild (bearings, chain, diff carrier) is 8-10 hours and requires specialized knowledge. Many owners swap to NP205 or NP208 for reliability.

Estimated cost: $300-600 for seals/minor work; $1,200-2,200 for rebuild; $800-1,500 for case swap

Typical onset: 90,000-140,000 mi

Symptoms: Transmission fluid leaking from pan, tail housing, or modulator, Delayed engagement into gear, Slipping on 2-3 shift, Shuddering at highway speed from worn torque converter

Fix: External seal and gasket work is 2-4 hours. Modulator replacement is 30 minutes. Full rebuild with torque converter runs 12-16 hours. These transmissions are robust but age and heat cycling cause seal failures.

Estimated cost: $200-500 for seals/gaskets; $1,800-3,200 for full rebuild

Typical onset: 70,000-120,000 mi

Symptoms: Excessive play at steering wheel (more than 2 inches), Wandering at highway speed, Clunking when turning from center, Leaking gear oil from steering box

Fix: Adjust steering box first (free, 15 minutes). If worn internally, rebuild or replace box (3-4 hours with alignment). Pitman arm, idler arm, and tie rod ends often need replacement simultaneously. Don't overlook frame cracks around steering box mount on rusty trucks.

Estimated cost: $150-400 for adjustment/linkage; $600-1,200 for box replacement and frontend work

Typical onset: 80,000-130,000 mi

Symptoms: Grinding noise from front wheels, Wheel wobble or play when jacked up, Grease leaking from hub cap, 4WD won't engage due to worn locking hub mechanism

Fix: Manual locking hubs wear and need rebuild kits or replacement (1.5 hours per side). Wheel bearings should be repacked every 30k or replaced if pitted (2 hours per side with new seals). Spindle bearing and seal work adds another hour per side.

Estimated cost: $300-700 per side for bearings/hubs

Symptoms: Hard starting when hot, Flooding or fuel smell, Rough idle or stalling, Fuel leaking from carburetor base or lines, Poor fuel economy

Fix: Rochester or Quadrajet carburetors develop vacuum leaks, worn throttle shafts, and deteriorated accelerator pump diaphragms. Rebuild takes 3-5 hours including adjustment. Fuel lines and rubber hoses rot and need replacement. Ethanol fuel accelerates deterioration.

Estimated cost: $250-600 for carburetor rebuild; $150-350 for fuel line replacement

Symptoms: Intermittent gauge operation, Lights flickering or not working, Blown fuses, Melted wire insulation under hood or dash, No-start from corroded bulkhead connector

Fix: Single-wire GM system is simple but 50-year-old cloth and rubber insulation cracks. Troubleshooting takes 1-3 hours per circuit. Bulkhead connector cleaning/repair is 2 hours. Full harness replacement (aftermarket) is 12-20 hours but rarely necessary.

Estimated cost: $100-400 for typical repairs; $800-1,500 for major harness work