1973 PONTIAC BONNEVILLE

Typical onset: 90,000-140,000 mi

Symptoms: Delayed engagement from Park to Drive, especially when cold, Slipping between 1st-2nd or 2nd-3rd shifts under acceleration, Burnt transmission fluid smell, dark/black fluid on dipstick, Whining or grinding noises during shifts

Fix: Full transmission rebuild with new clutch packs, bands, seals, and torque converter. Expect 12-16 hours labor for removal, rebuild, and reinstallation. TH400 units are more robust but both suffer from worn forward clutches and hardened seals by this mileage. Trans cooler lines often corroded and should be replaced simultaneously.

Estimated cost: $1,800-3,200

Symptoms: Hard starting when hot, requires excessive cranking, Rough idle, hesitation, or stumble during acceleration, Black smoke from exhaust indicating rich condition, Fuel leaking from carburetor base or accelerator pump, Poor fuel economy even for a 455 (below 8 mpg)

Fix: Rochester Quadrajet carburetors have rubber components that deteriorate from ethanol fuel. Complete rebuild with ethanol-compatible kit runs 4-6 hours including tuning. Often find cracked floats, hardened accelerator pump, and warped throttle shafts. Many owners opt for aftermarket Edelbrock replacement for reliability. Fuel filters clog frequently from tank sediment—replace every 10,000 miles.

Estimated cost: $450-950

Typical onset: 60,000-100,000 mi

Symptoms: Excessive clunking when shifting from Park to Drive or Reverse, Visible engine movement when revving in Park, Vibration through floor and steering wheel at idle, Transmission tunnel contact noise on acceleration

Fix: Rubber mounts deteriorate and collapse, especially on 455-equipped cars due to torque and weight. Transmission mount is most common failure—2 hours labor. Engine mounts require 3-4 hours as exhaust must be partially dropped on driver side. Replace all three simultaneously as labor overlaps. Original-style mounts last 50k-70k miles; urethane upgrades available.

Estimated cost: $350-650

Typical onset: 120,000-180,000 mi

Symptoms: Rattling noise from timing cover on cold start, disappears after 30 seconds, Erratic idle timing, won't maintain tune despite carburetor adjustments, Backfiring through carburetor or exhaust, Check timing shows 8-12 degrees variation from spec

Fix: Pontiac V8s use nylon-toothed cam gears that wear and chunk out, creating excessive chain slack. Requires timing cover removal, new chain/gear set, and front seal replacement—8-10 hours labor. Must set valve timing precisely on reassembly. Often discover worn fuel pump eccentric and oil pump drive simultaneously. High-mileage 455s sometimes reveal cam lobe wear requiring full rebuild at this point.

Estimated cost: $800-1,400

Typical onset: 140,000-200,000 mi

Symptoms: Blue smoke on deceleration or at startup, Consuming 1+ quart of oil every 500-800 miles, Loss of compression, sluggish acceleration, Excessive crankcase pressure, oil pushed past valve covers or dipstick

Fix: Worn piston rings allow combustion gases into crankcase and oil past rings into cylinders. Full engine-out rebuild with new rings, hone, bearings runs 30-40 hours. Most shops recommend full rebuild at this stage as bores show taper and ridge. 455s have thin cylinder walls—check for core shift before boring. Some owners opt for reman long-block swap at 25-30 hours labor.

Estimated cost: $3,500-6,500

Typical onset: 80,000-130,000 mi

Symptoms: Whining or groaning noise when turning, especially at low speeds, Power steering fluid leaking from pump or hoses, Stiff steering or intermittent loss of assist, Fluid appears burnt or contaminated

Fix: Saginaw pumps develop shaft seal leaks and bearing wear. Rebuild kits available but labor to access pump (3-4 hours) often makes reman replacement more cost-effective at similar price. High-pressure hoses crack from heat and age—inspect thoroughly. Flush system when replacing pump as metal contamination damages new unit.

Estimated cost: $300-550