The 1971 Blazer is a solid truck when maintained, but age-related fatigue of drivetrain mounts, fuel system degradation, and wear on high-mileage small-blocks are the main concerns. These are 50+ year-old vehicles now, so expect restoration-level work rather than typical maintenance.
Transmission and Engine Mount Failure
Common · medium severitySymptoms: Clunking on acceleration or deceleration, Excessive drivetrain vibration, Visible sagging or torn rubber on mounts, Shifter slop or hard engagement
Fix: Original rubber mounts deteriorate after decades regardless of mileage. Transmission mount is most critical and fails first. Plan 2-3 hours labor to replace trans mount, 4-6 hours if doing all engine and trans mounts together while you're under there.
Estimated cost: $300-800
Small-Block V8 Bottom-End Wear (307/350)
Common · high severityTypical onset: 120,000-180,000 mi
Symptoms: Heavy knocking on startup that quiets when warm, Low oil pressure at idle (under 10 psi hot), Metal shavings in oil, Blue smoke on deceleration
Fix: Main and rod bearings wear out, especially if oil changes were neglected. The 307 is particularly prone due to smaller journals. Full rebuild with machine work runs 25-35 hours labor, or 15-20 hours for a crate long-block swap. Budget more if cylinders need boring.
Estimated cost: $3,500-6,500
Head Gasket Failure (All Engines)
Occasional · high severityTypical onset: 80,000-150,000 mi
Symptoms: White smoke from exhaust, Coolant loss with no visible leaks, Milky oil on dipstick, Overheating under load, Rough idle and misfires
Fix: Original composite gaskets fail, worsened by improper torque or overheating. Single head is 8-12 hours labor including surface inspection and valve job if needed. If both sides are weeping, do both—you're already in there. Always check for head warpage and cracks.
Estimated cost: $1,200-2,800
Manual Transmission Rebuild (SM420 or SM465)
Occasional · medium severityTypical onset: 150,000-200,000 mi
Symptoms: Grinding into second gear, Jumping out of gear under load, Gear oil leaking from front or rear seals, Hard shifting when cold
Fix: The SM420 four-speed and SM465 are tough but not immortal. Synchros wear, particularly second gear. Full rebuild with new bearings, synchros, and seals runs 10-14 hours labor. Often the input shaft bearing is the culprit on high-mile units.
Estimated cost: $1,800-3,200
Fuel System Degradation
Common · medium severitySymptoms: Hard starting after sitting, Stumbling and stalling at idle, Fuel smell in cab or engine bay, Visible rust particles in fuel filter
Fix: 50-year-old tanks rust from inside, rubber fuel lines crack and weep, mechanical fuel pumps lose pressure. Replace all rubber lines, filters, and pump as preventive—about 4-6 hours. Tank replacement or sealing adds another 6-8 hours if rusted through.
Estimated cost: $600-1,500
250ci I6 Crankshaft and Main Bearing Failure
Occasional · high severityTypical onset: 140,000-200,000 mi
Symptoms: Deep knocking from lower engine, Sudden catastrophic oil pressure loss, Metallic rattling that worsens with RPM
Fix: The inline-six is durable but when mains let go, it's often terminal due to crankshaft damage. If the crank is scored, it needs grinding or replacement—full rebuild is 20-28 hours. Sometimes cheaper to swap in a good used long-block than machine the original.
Estimated cost: $2,800-5,000
Piston Ring Blow-By and Cylinder Wear
Occasional · medium severityTypical onset: 100,000-160,000 mi
Symptoms: Blue smoke on startup and acceleration, Excessive crankcase pressure (oil cap pops off), High oil consumption (quart per 500-800 miles), Loss of power and compression
Fix: Rings wear or cylinder walls glaze over. Rings-only job is 14-18 hours if cylinders don't need boring, but at this age expect a full rebuild with bore and hone. Re-ringing without addressing worn cylinders is a waste of money.
Estimated cost: $2,500-4,800
Buy one if you're handy or have a trusted mechanic—they're simple and parts are cheap, but assume you're buying a project that needs systematic refurbishment of 50-year-old components, not a turnkey driver.
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.