The 1987 C10 is a mechanically simple, body-on-frame workhorse with robust drivetrains, but 35+ years of age means worn engine internals, transmission mounts collapsing from fatigue, and fuel system corrosion are the norm. The TH700R4 4-speed overdrive automatic is the Achilles heel—less durable than the older TH350.
TH700R4 Transmission Failure (3rd/4th Gear Clutch Pack)
Common · high severityTypical onset: 120,000-180,000 mi
Symptoms: Slipping or flare on 2-3 or 3-4 upshift under load, No overdrive engagement on highway, Burnt transmission fluid smell, dark brown or black fluid, Check engine light (if equipped) or erratic speedometer
Fix: Full rebuild or replacement. Internal clutch packs burn out from inadequate lubrication or towing abuse. Rebuild takes 8-12 hours labor; remanufactured unit swap cuts that to 6-8 hours but costs more upfront.
Estimated cost: $1,800-3,200
Small Block Chevy Worn Piston Rings / Oil Consumption
Common · medium severityTypical onset: 150,000-220,000 mi
Symptoms: Blue smoke on startup or deceleration, Burning 1+ quart of oil every 500-800 miles, Loss of compression (wet vs. dry test confirms rings), Fouled spark plugs, rough idle when cold
Fix: Requires engine removal, complete disassembly, honing cylinders, new rings/bearings/gaskets. Full rebuild is 18-24 hours labor; many owners opt for reman long block swap (12-16 hours) to save time.
Estimated cost: $2,500-4,500
Collapsed or Torn Transmission Mount
Common · medium severityTypical onset: 80,000-140,000 mi
Symptoms: Clunk or bang when shifting from Park to Drive or Reverse, Vibration felt through floor at idle in gear, Visible sag or cracking in rubber mount when inspected from below, Driveline angle changes, can accelerate U-joint wear
Fix: Replace rubber crossmember mount. Requires supporting transmission with jack, unbolting crossmember. 1-1.5 hours labor, straightforward job.
Estimated cost: $120-250
Fuel Tank and Fuel Pump Corrosion (Carbureted Models)
Occasional · medium severitySymptoms: Hard starting after sitting, especially hot restarts, Sputtering or stalling under acceleration, Visible rust or pinholes in steel fuel tank, Sediment clogging inline fuel filter frequently
Fix: Steel tanks rust from inside due to ethanol fuel and age. Mechanical fuel pump diaphragms harden. Tank drop and replacement 3-4 hours; pump replacement (mounted on block) 1 hour. Often done together.
Estimated cost: $400-900
6.2L Detroit Diesel Injection Pump Failure
Occasional · high severityTypical onset: 120,000-180,000 mi
Symptoms: Hard starting, long cranking before engine fires, Black smoke under load, loss of power above 2000 RPM, Fuel in crankcase oil (dilution from leaking pump seals), Rough idle, uneven cylinder contribution
Fix: Stanadyne DB2 injection pump wears internally; seals fail. Pump replacement requires timing setup, 4-6 hours labor. Remanufactured pump core charge applies. These engines are slow and underpowered even when healthy.
Estimated cost: $1,200-2,000
Valve Guide Wear and Exhaust Valve Seat Recession (Unleaded Fuel)
Occasional · medium severityTypical onset: 100,000-160,000 mi
Symptoms: Blue smoke on deceleration (valve guides), Exhaust popping or backfire on deceleration, Loss of compression in one or more cylinders, High oil consumption despite good rings
Fix: Cylinder heads need removal, machining for hardened seats (pre-1971 heads especially), new guides, valve job. Heads-off labor 10-14 hours; machining/parts extra. Preventable with regular valve adjustments (solid lifter engines).
Estimated cost: $1,200-2,400
Frame Rust and Cab Mount Deterioration
Common · medium severitySymptoms: Cracking or tearing of rubber cab mounts, cab sags or shifts, Body creaking over bumps, door alignment issues, Visible surface rust or scaling on frame rails, especially behind cab, Severe cases: frame perforation near rear spring hangers or crossmembers
Fix: Cab mount replacement requires lifting cab off frame with hoist, 6-8 hours labor for all mounts. Frame rust repair varies widely—light surface rust is cosmetic; structural holes require welding/plating, 8-20 hours depending on extent.
Estimated cost: $600-3,000
Buy it if the frame is solid and the transmission shifts clean—engine work is straightforward and parts are cheap, but rotted frames and blown TH700R4s will cost more than the truck is worth.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.