Jim Grant's Tech Tips
97 Dodge Ram 1500, 4x4 Problems
"When I try to engage the four-wheel drive on my ‘97 Dodge Ram 1500, the four wheel drive light won't come on, and the wheels won't turn. But, the front drive shaft spins. I have been told contradictory stories from several mechanics. Could you tell me why my four-wheel drive does not work?
- Mary Long
The 4-wheel drive system on your vehicle has a mix of controls. When you move the 4-wheel drive lever into 4-wheel drive you’re engaging the 4-wheel drive part of the transfer case. On the transfer case there is a control switch that directs vacuum to a vacuum motor that is mounted on the front drive axle. When vacuum is applied to the “engage” side on the vacuum motor the motor in turn moves a shifting lever to lock in the front drive axle for the 4-wheel drive. The switch that turns on the 4-wheel drive engage light is mounted on the housing that holds the 4-wheel drive vacuum motor. Therefore, when the motor moves the shifting fork on the front axle into the 4-wheel drive position the light will be turned on. It’s not uncommon for moisture to cause corrosion to form on the plunger that the vacuum motor moves, causing it to stick. In addition, the vacuum switch that sends the signal the vacuum motor can be bad or a vacuum line to the vacuum motor can be cracked, pinched or even disconnected. Diagnosis is not a big deal on your truck. A vacuum gauge, vacuum pump and a test light are about all that is needed to determine just why your front axle is not locking in when needed.