1971 GMC SPRINT

Typical onset: 80,000-120,000 mi

Symptoms: Engine rattling on cold start that subsides when warm, Rough idle and poor throttle response, Check engine backfiring or won't start if chain jumps, Metal shavings in oil

Fix: Timing cover removal, chain and gear replacement, new oil pump recommended while you're in there. 6-8 hours labor for experienced tech, more if oil pan needs dropping. Original nylon-tooth cam gears disintegrate over time—this is not optional maintenance on a 50-year-old engine.

Estimated cost: $800-1,400

Symptoms: Visible rust perforation along frame rails behind cab, Bed sitting unevenly or loose, Cracking around bed mount bolt holes, Sagging rear end under load

Fix: These unibody-cab-on-frame hybrids rot where the bed bolts to frame and along rear frame sections. Repair requires sandblasting, cutting out bad metal, welding in patch panels or new frame sections. 12-20 hours depending on severity. Some require full frame-off if structural integrity is compromised.

Estimated cost: $2,000-5,500

Typical onset: 90,000-140,000 mi

Symptoms: Delayed engagement into reverse or drive, Slipping between 1-2 shift under load, Red fluid pooling under bellhousing or tailshaft, Burnt transmission fluid smell

Fix: Common failures include rear seal, modulator, and worn clutch packs in high-mileage units. External seal replacement is 2-3 hours; full rebuild is 8-12 hours. If previous owner towed heavy without cooler, expect internal damage. TH400 behind big-blocks typically lasts longer than TH350.

Estimated cost: $400-2,800

Symptoms: Hard starting when cold, Black smoke and flooding, Hesitation off idle or flat spots during acceleration, Fuel leaking from throttle shafts or base gasket

Fix: Quadrajets are excellent when fresh but suffer from dried-out gaskets, warped throttle shafts, and clogged passages after decades. Professional rebuild takes 3-4 hours including R&R. Many owners swap to Holley or Edelbrock instead (4-5 hours with tuning). DIY rebuild kits run $60 but require patience.

Estimated cost: $350-900

Typical onset: 100,000+ mi

Symptoms: Howling or grinding from rear that changes with speed, Gear oil leaking at wheel hubs, Hot smell from rear wheels after driving, Play in axle shaft (C-clip failure)

Fix: 12-bolt and 10-bolt rear ends both develop bearing wear and seal leaks. Bearing replacement requires axle shaft removal, pressing old bearings, and installing new seals—4-5 hours per side. C-clip-style axles can drop out if bearing fails completely, creating severe safety hazard.

Estimated cost: $600-1,200

Symptoms: Doors sag and require lifting to close, Wind noise at highway speeds, Striker plate worn oblong, Door won't stay open on incline

Fix: GM's bolt-on hinges wear bushings and pins after 50 years of use. Hinge pin kits available but proper fix involves removing door, sandblasting hinges, welding up worn holes, and re-drilling. Alignment-critical work—3-4 hours per door for quality results.

Estimated cost: $400-800

Typical onset: 80,000+ mi

Symptoms: Power steering fluid dripping from box, Increased steering effort when cold, Groaning noise when turning at low speed, Fluid level dropping regularly

Fix: Sector shaft seal and input shaft seal both leak with age. Rebuild kits available but require box removal and specialized tools—6-8 hours. Many opt for remanufactured box swap instead (3-4 hours). Leaks rarely cause failure but empty reservoir will destroy pump.

Estimated cost: $350-950