Front Axle Servo

[imaybail]

Going through my new to me 99 3500 and came across a vacuum servo on the front axle. Wondering what this is for since my truck has the shifter on the floor for the four wheel drive.

Having some issues with the ABS/Brake lights on the instrument panel and have read lots of posts on the issue but still haven’t found a solution to the problem. Brakes work fine, just have the idiot lights to deal with. Found a connector unplugged on the ABS controller, but when I plug it in the pump runs constantly. Seems like I may have a bad controller.

Also found that I,have a leak somewhere on the front passenger side. Have to track that down.

 

[petersonj]

Going through my new to me 99 3500 and came across a vacuum servo on the front axle. Wondering what this is for since my truck has the shifter on the floor for the four wheel drive.

That vacuum controlled motor on the front axle is part of the CAD unit on the front axle (called a central axle disconnect, I believe). The vacuum motor is controlled by a vacuum valve ( inside the transfer case, I think) which is operated by the transfer case shift lever.

So, when you shift the transfer case into 4wd, the vacuum motor on the CAD unit locks up the front axle disconnect feature at the same time the transfer case engages the front drive shaft.

Let me know if I can make this more confusing.

- John

 

[imaybail]

Didn’t realize there was more to the 4 wheel drive besides engaging the transfer case.
I had a Jeep once and that’s how it worked.