Symptoms
The dash 2WD/4WD control does nothing, the truck stays in one mode, or 4WD drops out. Hagerty says to check that 4WD engages on the fly; seals leak with age.
The fix, step by step
- Selec-Trac uses vacuum to shift between 2WD and 4WD.
- Check the vacuum lines from the engine to the reservoir, the dash switch and the transfer-case actuator for cracks or disconnected hoses, and test with a hand vacuum pump.
- On 1984–86 trucks, the transfer-case vacuum switch is a known replacement part.
- Fix any seal leaks at the yokes, then drain and refill the transfer case (Team Grand Wagoneer recommends a synthetic ATF-type fluid).
Tools & part numbers
- Hand vacuum pump
- vacuum hose
- sockets
- drain pan
- fluid pump
Where to buy the parts
Transfer case vacuum switch, 1984–1986Team Grand Wagoneer ↗Amazon ↗
Vacuum reservoir tank with mounting screws, 1974–1991Team Grand Wagoneer ↗Amazon ↗
NP208/NP228/NP229 yoke rubber sealing washer, 1980–1991Team Grand Wagoneer ↗Amazon ↗
100% synthetic transfer case fluid, 1980–1991Team Grand Wagoneer ↗Amazon ↗
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Rated for a competent home mechanic with a decent tool kit. Confirm torque figures, fluids and procedures against the factory service manual for your VIN, support the truck on stands rather than a jack, and work at your own risk (disclaimer). Some parts links are affiliate links, which pay us a small commission at no cost to you.