I have a 1991 318 4x4, and I have had some issues with the 4x4 this winter.

First it wouldn't engage when it got cold out, so I dumped the front diff fluid, which was pretty thick and not in great shape. I also replaced the vacuum lines at the front actuator, and put a new switch in the transfer case, but didn't touch the vacuum lines at the transfer case.

This seemed to help greatly, 4x4 worked reliably after that. That is until we got a big snowfall a couple of weeks ago. I took the truck to work, and most of the way was driving through 6-12 inches of snow, with drifts 1.5+ feet. 4x4 worked great all the way there, which is an hour drive, but on the way home my 4x4 stopped working. Needless to say I ended up getting stuck, and while waiting for my neighbors to show up to help pull me out, I pulled off the vacuum lines at the front motor, and noticed that neither line had any vacuum. We got the truck back to their heated shop and let it thaw out and 4x4 started working again.

This past weekend I replaced the vacuum lines at the transfer case, and thought I had the problem fixed, but again we got about 6 inches of snow, and I took the truck to work, and it seems to have frozen up again, but with the front axle locked (which is the better way for it to freeze up).

Now I can't have my 4x4 stop working or be unreliable every time I drive through a bit of snow, does anyone else have this problem? I'm going to disconnect the vacuum lines at the CAD motor, and at the transfer case and try blowing out the metal lines to see if that makes a difference. I also haven't put my skid plates back on so that may help, or may make things worse if it packs full of snow. But was wondering if anyone has any other ideas or has had this issue before and has fixed it? Thanks!

 

The CAD is a common problem. Unfortunately there are no replacements, so junkyard or try to modify one to work for your application. Or modify your CAD to always stay engaged, there is no problem while driving on the streets since the transfercase disconnects the front driveshaft anyways.

 

It's not the CAD motor that is freezing, it is the lines themselves, the motor seems fine from what I can tell. I have thought about just running a vacuum line straight from the engine down to the CAD Motor to leave it always engaged, and plug the other port. My 4x4 light will be on all the time then, but I could always just buy a Transfer Case switch from a 94+ and wire it to my light.

 

So just an update for anyone else that is having CAD issues when driving through deep snow.

I did some diagnosing over the weekend, and noticed that of the four vacuum hoses going to the Transfer Case Switch, only two were frozen. One was the line that goes from the engine to the transfer case switch, and the other one was the line from the transfer case switch to the vacuum reservoir. My lines going from the transfer case switch to the CAD motor were fine and clear. Being that it is vacuum both of these lines are pulling air from the transfer case switch.

I took off the plug that goes onto the transfer case switch, and on closer inspection, it looks like it had seen better days, and I don't believe it was sealing properly. With lots of snow, it would suck water and snow into the leaking plug, and once it sat for a bit, would eventually freeze up. I just took out the plug, and ran the vacuum lines directly to the switch, and all is well again. Now just to find some deep snow to test out my theory.

Just figured I'd post an update if anyone else is having this issue, as its frustrating that when you need 4x4 to go through a foot of snow, it causes it to freeze up.