Symptoms
The transfer case shifts into 4WD and the 4WD light may come on, but the front wheels don't drive. Or the axle grinds, won't disengage, or works only sometimes. Cold weather can make it worse when water freezes in the vacuum lines.
The fix, step by step
- RamCharger Central's KThaxton gives the quickest first test.
- With the engine running, pull both vacuum lines off the CAD motor on the axle and note which one has vacuum in 2WD.
- Then shift into 4WD: the vacuum should switch to the other line.
- If it doesn't, the vacuum switch on the transfer case is bad.
- If it does, look for leaks in the lines and the vacuum reservoir, then pull the motor and check that the fork and collar slide freely.
- Torque King's list of usual causes adds a leaking or bent vacuum motor, worn fork pads, worn shift collar splines and swollen rubber connectors at the switch.
Tools & part numbers
- Hand vacuum pump and gauge
- basic hand tools
- drain pan (gear oil may leak from the CAD housing)
Where to buy the parts
QU10569 transfer case vacuum switch (NP241 with CAD)Torque King 4x4 ↗Amazon ↗
QA4628 CAD shift fork with pads (lists 1985–93 Ramcharger)Torque King 4x4 ↗Amazon ↗
QU40224 Spicer vacuum shift motor kit (Torque King lists 1989–2002)Torque King 4x4 ↗Amazon ↗
QU40090 CAD housing gasketTorque King 4x4 ↗Amazon ↗
Hunting a used or discontinued part? Search eBay Motors for Dodge Ramcharger (1981–1993) parts →
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.