1977 PONTIAC BONNEVILLE

Symptoms: rough idle and stalling at stops, hesitation or stumble on acceleration, black smoke from exhaust, fuel economy below 10 mpg, flooding or hard starting when hot

Fix: Rochester Quadrajet carbs need frequent rebuilds due to dried-out accelerator pump cups, worn throttle shafts, and clogged jets from ethanol fuel. Full rebuild kit plus carb cleaning takes 3-4 hours if you know what you're doing. Many owners convert to Edelbrock or Holley to avoid ongoing headaches. Factor vacuum line replacement and choke adjustment.

Estimated cost: $350-750

Typical onset: 80,000-140,000 mi

Symptoms: delayed engagement into gear, slipping between 1st and 2nd or 2nd and 3rd, burnt transmission fluid smell, no movement in drive or reverse, overheating after highway use or towing

Fix: These transmissions are generally bulletproof but neglected fluid changes kill them. Failed modulator valves and worn clutch packs are common. Full rebuild with updated friction materials, bands, and seals runs 12-16 hours labor. External cooler lines rot out and cause fluid loss. Add external auxiliary cooler if towing or in hot climates. Transmission mount failures (2 hours labor) cause clunking and accelerate internal wear.

Estimated cost: $1,800-3,200

Typical onset: 60,000-100,000 mi

Symptoms: blue smoke on startup or acceleration, burning 1+ quart of oil every 500-800 miles, fouled spark plugs, reduced power and compression, oil coating on exhaust pipes

Fix: The 301 Pontiac and Chevy 305 V8s used soft piston rings that wear prematurely. Short-term fix is heavier oil (20W-50) but real solution requires engine-out rebuild with quality ring set, cylinder hone, and new valve seals. Figure 20-28 hours labor for full tear-down. Many owners swap to 350 Olds or Chevy from junkyard instead of rebuilding weak smog motors. 350 Olds and 403 Olds engines hold up better but still see ring wear past 120k.

Estimated cost: $2,800-4,500

Typical onset: 100,000-150,000 mi

Symptoms: deep knocking sound that increases with RPM, metallic rattle on cold startup, low oil pressure at idle, metal shavings in oil pan, vibration through floor at idle

Fix: Low oil pressure from clogged pickup screens or neglected oil changes leads to spun main bearings. Requires full engine removal, crankshaft inspection/machining, and bearing replacement. If crank journals are worn beyond spec (.010 undersize or worse), you need crank grinding or replacement. Total job runs 24-32 hours including R&R. Often cheaper to swap in used engine from salvage yard than rebuild badly-worn bottom end.

Estimated cost: $3,200-5,800

Typical onset: 70,000-110,000 mi

Symptoms: coolant loss with no visible external leaks, white smoke from exhaust, rough idle and high idle speed, engine overheating, hissing sound from engine bay

Fix: Paper and cork intake gaskets deteriorate causing vacuum leaks and coolant seepage into cylinders. On 301/350/403 engines, manifold removal requires pulling distributor, carburetor, and all vacuum/emissions lines. Job takes 5-7 hours including surface prep and reassembly. Use modern composite gaskets, not OEM paper. Check EGR valve and other vacuum-operated emissions components while manifold is off.

Estimated cost: $450-900

Symptoms: clunking over bumps, visible daylight gaps between body and frame, doors not closing properly, sagging body at rear quarters, rust holes visible in frame rails behind front wheels

Fix: B-body frames rust badly in salt-belt states, especially at body mount points and rear spring hangers. Rubber body mounts compress and rot, causing body movement. Body mount replacement (8 mounts) takes 6-8 hours with proper jacks and safety stands. Frame rust requires professional welding and plating; minor rust can be wire-brushed and POR-15 treated, but structural damage means walk away. Inspect before purchase.

Estimated cost: $600-1,200