The 1970 Coronet is a solid B-body Mopar that shares mechanical DNA with the Charger and Road Runner. Most survivors have the 318 or 383, and while the drivetrains are fundamentally stout, age-related issues dominate—these are 50+ year-old cars where rubber, seals, and metallurgy finally give up.
Timing Chain Stretch and Gear Wear
Common · high severityTypical onset: 80,000+ mi or unknown history
Symptoms: Rough idle with retarded cam timing, Hard starting when hot, Metallic rattling from front of engine at startup, Loss of power, misfiring under load
Fix: Replace timing chain, gears, and tensioner as a set. The nylon cam gear teeth disintegrate over time. Requires front cover removal, harmonic balancer puller, new gaskets, and timing degree check. 4-6 hours labor for a 318/383, add 1-2 hours for bigger blocks due to accessory crowding.
Estimated cost: $600-1,200
Carburetor Flooding and Fuel Boiling (Carter/Holley)
Common · medium severitySymptoms: Hard hot restarts, engine floods after sitting, Black smoke, fuel smell in engine bay, Fuel dripping from carb base or bowls, Hesitation, stumble off idle when hot
Fix: Old ethanol-degraded gaskets and dried-out needle/seat assemblies leak. Heat soak from modern fuel causes vapor lock. Full carb rebuild with ethanol-compatible kit, or swap to electric fuel pump with return line. 2-4 hours for rebuild and tuning.
Estimated cost: $300-700
Torsion Bar Anchor Corrosion and Suspension Sag
Common · medium severitySymptoms: Front end sitting noticeably low, Uneven ride height side-to-side, Clunking from front crossmember over bumps, Torsion bar socket rust-through in lower control arm
Fix: Torsion bars themselves rarely fail, but the adjusting bolts seize and the rear anchors corrode in the crossmember. Worst cases need crossmember repair or replacement. Sag is fixed by cranking adjusters or replacing bars with HD units. Bushing and ball joint refresh while you're in there. 6-10 hours for full front suspension overhaul.
Estimated cost: $800-2,000
Rear Main Seal and Oil Pan Gasket Leaks
Common · low severityTypical onset: 60,000+ mi or after long storage
Symptoms: Oil dripping from bellhousing area or pan rails, Puddles under car after sitting overnight, Oil consumption without visible exhaust smoke
Fix: The rope-style rear main seal hardens and shrinks with age. Oil pan gaskets are cork and disintegrate. Rear main requires transmission removal (5-7 hours for auto, 4-6 for manual). Oil pan is easier but crossmember may need to be dropped. Often both done together.
Estimated cost: $700-1,400
TorqueFlite 727 Transmission Kickdown Linkage Issues
Occasional · medium severitySymptoms: Transmission won't downshift for passing, Sluggish acceleration, stays in high gear too long, Harsh or late upshifts
Fix: The external kickdown rod from carb to trans gets bent, seized, or disconnected during engine work. Without proper adjustment, line pressure drops and clutches slip prematurely. Adjustment is critical—too tight causes harsh shifts, too loose burns clutches. 0.5-1 hour for linkage service and adjustment.
Estimated cost: $80-200
Steering Box Play and Pitman Arm Wear
Common · medium severityTypical onset: 70,000+ mi
Symptoms: Excessive play at steering wheel (more than 2 inches of slop), Wandering on highway, constant correction needed, Clunking felt through steering column over bumps
Fix: Manual steering boxes wear internally and develop lash. Power steering boxes leak and lose adjustment. Pitman and idler arms wear out their tapered shafts. Full steering rebuild includes box rebuild/exchange, pitman, idler, tie rod ends, and alignment. 5-8 hours total.
Estimated cost: $600-1,300
Radiator Core and Heater Core Failure
Occasional · medium severitySymptoms: Overheating in traffic or on highway, Coolant leaking from radiator seams or tubes, Sweet smell in cabin, fogged windshield, wet passenger floor
Fix: Original copper/brass radiators corrode through after decades. Heater cores fail internally and leak into the cabin—requires full dash pad removal on non-AC cars, entire evaporator housing on AC cars. Radiator swap is 2-3 hours. Heater core is 8-12 hours due to dash disassembly.
Estimated cost: $400-800 radiator, $800-1,800 heater core
Buy it if the body is solid and the drivetrain has been maintained—mechanical parts are available and affordable, but rust and neglect will cost you double what a clean example would.
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.