1967 PONTIAC 2+2

Typical onset: 70,000-110,000 mi

Symptoms: Slipping on 2-3 shift under load, Burnt transmission fluid smell, Delayed engagement when cold, Metal particles in pan during fluid change

Fix: TH400 three-speed automatic wasn't designed for the 421's torque long-term. Cooler lines deteriorate, auxiliary cooler often bypassed or clogged. Full rebuild with upgraded clutches, bands, and external cooler installation takes 12-16 hours. Transmission oil cooler replacement alone is 3-4 hours if caught early.

Estimated cost: $2,800-4,200

Typical onset: 80,000-140,000 mi

Symptoms: Deep knocking at idle that worsens with RPM, Low oil pressure below 20 psi hot at idle, Metallic debris in oil filter, Vibration through drivetrain

Fix: Main and rod bearings wear from inadequate oiling in high-performance use or deferred oil changes. Crankshaft often needs grinding 0.010" or 0.020" undersize. Complete teardown requires pulling engine, 25-35 hours for short block work with machine shop time. Piston ring replacement typically done simultaneously.

Estimated cost: $4,500-7,500

Typical onset: 50,000-90,000 mi

Symptoms: Clunk when shifting into gear, Excessive driveline vibration at highway speed, Transmission tailshaft visibly sagging, Harsh engagement into reverse

Fix: Rubber mount deteriorates from heat and age, allowing excessive transmission movement. Combined with engine mounts, this creates severe driveline angle issues. Replacement is straightforward at 1.5-2.5 hours but requires proper support of transmission.

Estimated cost: $180-350

Symptoms: Hard starting after sitting, Stumble on acceleration, Flooding when hot, Rough idle that improves with choke applied

Fix: Rochester or Carter AFB carburetors gum up from modern ethanol fuel, especially in stored vehicles. Fuel filter location before pump means debris circulates. Complete carburetor rebuild with new accelerator pump, float, and jets takes 3-5 hours. Tank cleaning recommended if vehicle sat over 2 years.

Estimated cost: $450-850

Typical onset: 60,000-100,000 mi

Symptoms: Clutch pedal feels spongy or has excess travel (manual), Grinding noise when clutch engaged, Excessive crankshaft end play over 0.012", Transmission difficult to shift or grinds

Fix: Thrust bearing wears from clutch riding or aggressive launches. Pontiac 421 uses rear thrust surface prone to failure. Requires complete engine removal and crankshaft R&R, 20-30 hours. Often discovered during bearing replacement. Some cranks need welding and remachining if thrust surface damaged.

Estimated cost: $3,500-6,000

Typical onset: 70,000-120,000 mi

Symptoms: Ticking or tapping at idle that quiets with RPM, Loss of power at high RPM, One cylinder running lean or misfiring, Hydraulic lifter pump-up causing valve float

Fix: Hydraulic lifters collapse from varnish buildup or spring fatigue. Pushrod geometry critical on 421; worn rocker shafts cause accelerated valve guide wear. Top-end work with lifter replacement, valve job, and guide work takes 18-24 hours. Full engine rebuild often more cost-effective at this point.

Estimated cost: $2,200-3,800