1991 FORD BRONCO

Typical onset: 80,000-150,000 mi

Symptoms: No overdrive engagement or slipping in 4th gear, Shuddering or vibration during highway cruising, Transmission overheating, burnt fluid smell, Hard or delayed shifts between 2nd and 3rd

Fix: E4OD overdrive section fails due to inadequate lubrication and weak servo pistons. Transmission oil cooler lines also corrode internally, sending debris into valve body. Full rebuild with upgraded servos and bands runs 12-18 labor hours; cooler replacement adds 2-3 hours. Many shops recommend auxiliary cooler install during rebuild.

Estimated cost: $2,200-3,800

Typical onset: 100,000-140,000 mi

Symptoms: No-start condition, cranks but won't fire, Stalling at operating temperature or under load, Sputtering or hesitation above half throttle, Whining noise from rear of vehicle

Fix: The in-tank pump on the dual-tank system wears out, especially on trucks that regularly switch between tanks. Requires dropping the rear tank (19-gallon), replacing pump assembly and often the fuel sending unit. Single-tank conversions are popular. 3-4 labor hours if tanks aren't rusty.

Estimated cost: $450-750

Typical onset: 90,000-150,000 mi

Symptoms: Oil pooling under rear of engine or transmission bellhousing, Oil drips after vehicle sits overnight, Visible oil coating on flywheel through inspection cover, Low oil level despite no visible leaks up front

Fix: Windsor engines develop rear main seal leaks as the two-piece seal hardens. Requires transmission removal on 4WD models. Oil pan gaskets also fail due to inadequate RTV application from factory and rust-through on older pans. Rear main is 8-10 hours with trans drop; pan gasket alone is 3-4 hours due to crossmember and steering linkage interference.

Estimated cost: $800-1,600

Typical onset: 70,000-120,000 mi

Symptoms: 4WD won't engage, dash indicator blinks, Grinding noise when attempting to shift into 4WD, 4WD engages but won't disengage (stuck in 4WD), Intermittent engagement, works cold but fails when warm

Fix: Electronic shift motor on BW1356 transfer case seizes or strips internal gears due to corrosion and lack of lubrication. Motor is external and replaceable without case disassembly, but often the shift fork inside is also worn. Motor replacement is 2-3 hours; if fork is damaged, case must come out (6-8 hours total).

Estimated cost: $400-1,200

Symptoms: Fuel smell in cab or under vehicle, Fuel puddle on ground near frame rail behind cab, Selector switch doesn't change tanks or gets stuck, Check engine light with lean codes on one tank

Fix: Dual-tank systems use a frame-mounted selector valve that corrodes from road salt and develops internal leaks. Valve itself is cheap, but access requires removing heat shields and sometimes exhaust components. Steel fuel lines rust through at the valve connections. 2-4 hours depending on rust severity and line replacement needs.

Estimated cost: $300-700

Symptoms: Sudden no-start, no spark condition, Stalling when engine reaches operating temperature, Intermittent stalling in hot weather or stop-and-go traffic, Cranks strong but won't fire, no codes stored

Fix: The Thick Film Ignition (TFI) module mounted on the distributor fails due to heat cycling. This is a Ford-wide issue on 1983-1995 vehicles. Module replacement is 0.5 hours and cheap, but many techs relocate it to the fender well with a pigtail extension to improve cooling and longevity.

Estimated cost: $120-250

Typical onset: 80,000-130,000 mi

Symptoms: 4WD engages but front wheels don't pull, Hub won't lock or unlock, stuck in one position, Grinding or clicking from front hubs when turning, One wheel pulls in 4WD, the other freewheels

Fix: Manual locking hubs wear internally, especially if driven through water or mud without post-trip cleaning. Internal springs weaken and cams wear. Replacement hubs are straightforward—remove six bolts per side. Upgraded aftermarket hubs (Warn, Mile Marker) last longer. 1-2 hours for both sides.

Estimated cost: $200-450