i have an 01 dually with six speed, 4x4. bought it new.
my 4x4 has failed to work about 5times since i've owned it. everytime it fails, it has something to do with a vacuum line.

first time, the dealer said, "a hose came disconnected off the front axle". now up to this point, the truck has never been off road, not even in grass. so how does this vacuum line become dislodged?

the next few times it failed, it was diagnosed as the line having a leak or coming off front diff...."again".

most recent time, i pulled the lever to engage 4Wheel, the same thing. didn't work. first time i tried to use it this season....little bit of snow.

anyone have information on how to TS this problematic item? can i put a permanent fix on it.

thanks all

 

Take a look for yourself. There is nothing really complicated about it. There's a vacuum switch on the top of the transfer case with rubber lines coming out the top. Of those lines there are two which run down to the cross member where they attach to metal lines. Those lines run across the cross member and up the frame. Off those two metal lines, the rubber hoses reconnect and run down to the front axle CAD unit. If the lines are connected everywhere and intact then thats good.

Now a problem you NY area people will face is snow, ice, and lots of road salt. So if any moisture makes it into the lines and the moisture collects and freezes then the vacuum signal is plugged. Obviously if a rubber line cracks from drying out or corrosion then the vacuum is lost. And if the lines are pulling off the CAD then it would seem they're somehow too short. Dont really understand why they'd be short though.....

No matter, if you simply take a look for yourself you'll be able to easily identify whats going on. If you're unsure how the CAD system works, I'd be more than happy to explain and provide some links to better understand whats happening and why your 4wd may not be working.

 

And look at Posilock 4X4 for a permanent if not automatic fix.

I had one on my first truck, worked well and you never had to worry.

 

Ditto on the posilok cable, simple tools to install and pretty much foolproof.

 

I put a permalock on mine. I prefer running with a live front end anyway.

 

Anyone who hasn't installed a 2 lo kit on their CAD 4wd system is seriously missing the boat. I cant express enough how useful 2 lo is. I use it all the time for creeping around the property, moving trailers, pulling the boat out of the water, etc..... Its probably one of the best "functional" things I've installed on my truck, and it isnt an option without the CAD system.

 

^^Sure it is, just drop the front driveline....

 

I would sure like to know this!

Thanks!

 

+1.

But I don't like the design of the vac operated one that leaves the transfer case valve in control.

On mine, I use a toggle down by the transfer case shifter to control it directly, with the hoses bypassing the valve at the transfer case.

If you do it this way, the toggle becomes like locking your hubs on a manual hub truck. If it's out, you can shift right to 2low with the shifter.

And if you leave the front axle locked in, you can shift ***instantly*** to 4x4 high at freeway speeds. Plunks right in and out without the goofy delay at the shifter and waiting for the vac to engage the CAD.

To shift to 4x4 rolling with this setup from 2hi with CAD disengaged, I flip the CAD toggle and then immediately shift the transfer case. It's quicker this way but you have to be on the shifter quick or the CAD might grind. Shifting first and then flipping the CAD is fool proof, but slower.

 

When you shift to 4x4, the front output inside the transfer case has a synchro like a transmission rather than just a collar shift. This brings the front driveshaft diff gears etc. up to matching speed so the sleeve that the CAD actuates doesn't grind.

At the same time, a vacuum valve on the transfer case sends vacuum to the an actuator that slides a collar to lock in the passenger side axle shaft. As it locks in, a switch send connects to turn the 4x4 light on.

4x4 low leaves the CAD engaged and shifts a planetary gear set to reduce the the speed the transmission putting out.

I'm sure Katoom will be back to elaborate further.

 

You know me..... I love to elaborate. But instead, how about a link which should answer all the questions and even offer some troubleshooting as well. Diagnosing 4WD Engagement Problems on Dodge Ram pickups

 

Thank You Katoom and Totalloser for the information!

 

this was the first time i needed 4wd this season.

we had some snow this weekend, 1/23-24, but nothing where i am...still bitter cold out.

thanks for all the input...i'll havd to get underneath there and see whats going on.