1972 GMC C2500

Typical onset: 80,000-150,000 mi

Symptoms: Hard starting when hot, backfiring through carburetor on startup, Rough idle, hesitation under acceleration, Rattling noise from front of engine at idle, especially on cold start, Erratic timing, won't stay tuned despite distributor adjustments

Fix: Replace timing chain, gears, and tensioner. On big-blocks (396/402/454), common to find nylon-coated cam gear teeth stripped. Requires front cover removal, water pump off, harmonic balancer puller. Book time 4-6 hours depending on accessories and whether you're also doing oil pan gasket while you're in there. Use double-roller steel aftermarket chain, not OEM-style.

Estimated cost: $600-1,200

Symptoms: Visible holes or soft spots in cab corners behind doors, Rust bubbling along rocker panels below doors, Floor mat perpetually wet, water intrusion from underneath, Seat mounts loose or pulling through rotted floor

Fix: This is the killer on these trucks. Cab mounts trap moisture and floors rot from inside out. Rockers are double-wall and rust from between layers. Proper fix requires cab-off-frame work (8-12 hours labor), cutting out old metal, welding in patch panels or full floor pans. Half-measures with pop-riveted patches fail within two years. If rockers are gone, structural integrity is compromised—impacts safety in a collision.

Estimated cost: $2,500-6,000

Typical onset: 60,000-100,000 mi

Symptoms: Play in steering wheel exceeding 2-3 inches before wheels respond, Wandering on highway, constant correction needed, Clunking from front end over bumps, Grease leaking from steering box or tie rod ends

Fix: Manual recirculating-ball steering box can be adjusted for lash, but worn sector shaft means replacement box needed ($300-400 rebuilt). Tie rod ends, idler arm, and pitman arm typically all worn by now. Budget 3-4 hours for gearbox R&R, another 2-3 for full linkage overhaul and alignment. Expect to do this if the truck hasn't been maintained—50-year-old rubber and grease are shot.

Estimated cost: $800-1,500

Symptoms: Fuel smell in cab or engine bay, visible seepage at carb base, Black smoke from exhaust, loading up and fouling plugs, Hard starting after sitting, flooding condition, Fuel economy suddenly drops 30-40%, raw fuel dripping from tailpipe

Fix: Rochester Quadrajet carburetors have well-known issues with accelerator pump gaskets, needle-and-seat wear, and float problems after 40+ years. Rebuild kits run $50-80, but internal passages corrode if truck sat with old ethanol fuel. Figure 3-4 hours to remove, clean, rebuild, and dial in properly. Alternatively, swap to Edelbrock 1406 ($400) and never look back—2 hours install including new fuel line and kickdown linkage adjustment if auto trans.

Estimated cost: $300-700

Typical onset: varies widely

Symptoms: Pedal slowly sinking to floor when held at stop, Soft or spongy pedal feel despite bleeding, Brake fluid disappearing from reservoir with no visible external leaks, Total pedal loss—one pump works, second pump goes to floor

Fix: 1972 still used single-reservoir master cylinder on some builds—dangerous pre-dual-circuit design. Internal seals fail and truck loses ALL braking. Upgrade to dual-reservoir MC from 1973+ for safety ($80-150). Requires new proportioning valve and sometimes hard line modifications. 2-3 hours labor plus full brake system bleeding. DO NOT skip this if buying one—it's a life-safety issue.

Estimated cost: $250-500

Symptoms: Fuel gauge stuck on empty, full, or bouncing erratically, Fuel smell near driver-side rear cab corner, Fuel leaking from filler neck or tank straps when full, Difficulty filling—pump clicks off every few seconds

Fix: Steel tanks rust through from top (water sits on upper surface). Sending units fail from ethanol exposure. Filler necks corrode where they meet tank. Tank drop and replacement is 2-3 hours ($200-350 for aftermarket tank), sending unit another $80-120. If filler neck rusted, need new rubber hose and clamps too. Often combined with fuel pump replacement while you're under there (mechanical pump on block, $40 part).

Estimated cost: $400-700