I have a 95 3/4 ton 4X4. Yesterday when I tried to put it into 4 wheel drive, it stayed in two wheel drive. I moved the shifter into low 4 wheel and the gear ratio changed like it should, but it was still only two wheel drive. The "4X4" light on the dash didn't come on.

I'm hoping I don't hate the answers I get, but I'm preparing for the worst here. Any ideas?

Fred

 

Sounds like the CAD unit on the axle is not working, there should be a vacuum source going to the unit. it is supposed to engage the axles when in 4x4. i'd start there. if you can go to 4x4 low, the TC is working properly. the CAD unit failure is a common one.

 

my ford did the same thing when the transfercase whent out and it it still sitting with the tcase bad havent found the extra 1100 to buy a new one

 

I have a 95' 2500 as well. I can almost promise you that you have lost vacuum in the system, somewhere, or the vacuum servo on the CAD is simply rusted thru somewhere. Either one is relatively easy to diagnose. I would also replace line and check valves if they are original. Mine were rotted at 8 years.


Do your ac/heater vents ever switch settings without turning the selector ****? How are your brakes? Low vacuum would give you more of a "brick" feel to the pedal. Harder to apply than normal.

Does your cruise control work fine?

Good luck with your ride.

 

Don't go by the dash light. I have seen them go out. Put the truck in 4hi and lift the front end so both tires are off the ground. Spin the passenger side tire. If the driver's side spins the axleshaft is engauged and 4x4 works.

 

Thanks guys. Is replacing the CAD unit an easy shadetree fix? Also, don't laugh, but what does CAD stand for as I can't find one online when I search using CAD unit.

 

Thanks for the many replies. It's icy here and only my rear tires are spinning regardless of where the shifter is situated, I'm sure it isn't just a bad bulb. Thanks.

 

CAD is your central axle disconnect. Your left side, front axle shaft is one solid piece from the differential to the hub assembly.

On the passenger's side, you have a 2piece axle shaft. Some call it inner and outer, outer and intermediate, etc. The intermediate shaft goes from the differential, to the cad. Then an outer shaft goes from the cad, to the right wheel hub assembly.


What happens in the CAD when you shift into 4 wheel drive, a shift fork, controlled by a vacuum servo, slides acollar that hasacoupler attached to it. The ends of the intermediate, and right side axles shafts that face each other have splines cut into them. When the shift fork is actuated, it slides a collar thatcovers both axles simultaneously.

Because that right side now has a "solid shaft", the differential is live.

That axle being split on the right side is what eliminates the need for manual/auto hubs. You sinply have full time hubs, with a central axle disconnect.

If you loose proper vacuum, the CAD will not engage. If you place the truck in 4 wheel drive, and the CAD does not engage,.... the front axle will not be driven. The carrier will simply drive the passengers side of the diff and apply no power to either wheel.


I hope I didn't confuse ya more......Hope it helps a little.

I'm sure someone will whip up some pics. I personally need to see the item in front of me while a mechanic points things out.........LOL. I'm not always the fastest one out of the gate when it comes to reading comprehension.....LOL. PICS baby, PICS!!!!!!...lol


Anyway, good luck with your ride. Feel free to pm me if I can help ya with anything else. I have all the 95' Ram manuals. My tranny manuals are on loan at the moment. But I can cover anything else.


1995 Dodge Ram CTDs will someday rule the world.

Good luck with your ride.

 

Here is oneI am very fimilar with. I changed the two hoses on bottom to a more solid ruber line(Think i used fuel line) But the root cause was a fiiting on a exhaust screen.If you follow the vacuum linesunderthe truck around to somewhere under the master cylinder you will see the tubing end in what looks like a small little filter. This had a 90 degree fitting that was pushed in to far and not allowing any flow through that tubing.This one took me a few hours! Also you can unbolt the actuator from the front end and with the truck running have someone shift it back and forth to get a better idea of what is going on. GOOD LUCK

 

Another thing to add.... With the truck running you can pull the 2 vacuum line off the cad( Shifter fork) and see if there is vacuum at one of the hoses. Vacuumshould shift from one hose to the other dependingif the truck is in 2 wheel or 4 but there should always be vacuum on one or the other hoses.