The 1979 Mustang represents the tail end of the Mustang II era—a unibody Fox-adjacent platform with smaller dimensions and lighter construction than later Fox bodies. These cars are mechanically simple but suffer from age-related rust issues, weak drivetrains, and carburetor headaches typical of late-'70s smog-era engineering.
Timing Chain Stretch and Guides (V8 engines)
Common · high severityTypical onset: 80,000-120,000 mi
Symptoms: Rattling noise from front of engine on cold starts that subsides when warm, Rough idle or hesitation under acceleration, Check engine timing with light—often retarded 5-10 degrees from spec, Metal shavings in oil if guides have disintegrated
Fix: Replace timing chain, gears, and nylon-coated guides with double-roller chain kit. Requires front cover removal. 6-8 hours labor including oil pan gasket while you're in there. High-mileage 302s often need this.
Estimated cost: $800-1,400
Carburetor Issues (All engines—2.3L, 3.3L, 4.2L, 5.0L)
Common · medium severitySymptoms: Hard starting when hot or cold, Stalling at idle or when coming to stops, Black smoke from exhaust—running rich, Hesitation or flat spots during acceleration, Fuel smell from engine bay—leaking accelerator pump diaphragm
Fix: Carter YF (I4), Motorcraft 2150 (V6/V8), or Holley 6500 (302) carbs all gum up with ethanol fuel and old gaskets. Full rebuild kit plus labor: 3-4 hours. Many owners swap to Weber or Holley aftermarket for reliability. Vacuum line dry-rot compounds the problem.
Estimated cost: $350-650
Subframe and Torque Box Rust (Unibody Structure)
Common · high severitySymptoms: Visible rust perforation in rear torque boxes behind rear seats, Front subframe rails flaking or crusty where front suspension mounts, Clunking over bumps from loose subframe mounts, Floor pan rust-through near seat mounts, Rear spring perches rusting from inside trunk
Fix: These cars rust badly in the Midwest and Northeast. Torque box replacement requires cutting and welding patch panels—8-12 hours if you're good with a welder. Subframe work can exceed 20 hours if extensive. Parts are available but labor-intensive. Structural rust is a deal-breaker on many survivors.
Estimated cost: $1,500-4,000
Rear Axle Seal and Differential Leaks (7.5" and 8" rear ends)
Occasional · low severityTypical onset: 60,000-100,000 mi
Symptoms: Gear oil dripping from rear axle tubes or differential cover, Oil coating rear brakes causing reduced stopping power, Whining noise from rear end under load, Low fluid level found during inspection
Fix: Axle seals dry out and leak. Requires pulling axle shafts—2 hours per side. Pinion seal another 1.5-2 hours. Diff cover gaskets leak from overtightening or age. Easy fix but messy. If bearings are worn (whine), budget for full axle rebuild.
Estimated cost: $300-600
Rack-and-Pinion Steering Leaks and Looseness
Occasional · medium severityTypical onset: 70,000-110,000 mi
Symptoms: Power steering fluid leaking from rack boots, Excessive play in steering wheel—more than 2 inches, Groaning noise when turning at low speeds, Steering wanders or requires constant correction on highway
Fix: Mustang II uses a basic Ford rack unit that wears at the seals and develops internal slop. Rebuilt racks available but alignment required after replacement. 3-4 hours labor. Inner tie rod ends often worn simultaneously. Manual steering cars have less trouble but heavy effort.
Estimated cost: $450-800
Ignition Module and Distributor Failures (Duraspark II system)
Occasional · medium severitySymptoms: No-start condition—cranks but won't fire, Intermittent stalling when hot—restarts when cool, Backfiring through carburetor, Loss of power under load
Fix: The Duraspark II ignition module (mounted on distributor or fender) fails from heat cycling. Distributor shaft bushings wear causing timing scatter. Module replacement is 0.5 hours, distributor rebuild 2-3 hours. Carry a spare module in the glovebox—common roadside failure on hot days.
Estimated cost: $150-400
Heater Core Leaks (Dashboard removal required)
Occasional · low severityTypical onset: 80,000-130,000 mi
Symptoms: Sweet smell inside cabin, Coolant dripping on passenger-side floor, Foggy windshield that won't clear, Low coolant level with no external leaks visible, Oily film on inside of windshield
Fix: Heater cores rot from the inside out. Replacement requires full dashboard removal on Mustang II—8-10 hours labor. Many owners bypass the core with a loop if heat isn't needed (warm climates). A miserable job that's all labor, minimal parts cost. Flush cooling system first to verify it's actually the core.
Estimated cost: $600-1,200
Buy one if you find a rust-free Western car with documented maintenance—they're cheap to fix mechanically but structural rust makes most examples rotted beyond economical repair.
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.