Just when I thought everything that could go wrong this year I was proven wrong.

I had my 98 1500 318 4x4 in the shop earlier this week to have the rotors and pads replaced (they tried to yank the drums but they were rusted on). Last night I tried to go into 4-High and it never went in over the 1 mile stretch. This morning I shifted into 4-High and it took about a mile to engage and then disengaged within 1/4 mile after that.

The conditions this morning were a bit cold (-10 F) but the truck had been plugged into a block heater and been running to warm up for 20 minutes. Prior to this I had never once had the slightest problem with 4WD or the transmission other than the transmission going 2 years ago (dealer replaced). Given this I am inclined to think it was something the shop did, but I have no idea where to start the diagnostics.

 

Check the vacuum lines going to the CAD unit on the front axle. Could be the CAD itself or the switch on the TC also.

 

posi-lok my friend...look into it

 

see tech info here...
https://dodgeforum.com/forum/2nd-gen...t-working.html

 

Been there, seen that, etc, etc.

 

Update: I checked again today and it WILL shift into 4-Hi, but pops out with a moderate thunk if moderate acceleration is applied and/or turning. Checked again underneath and the vacuum lines seem fine. I am dropping it off at a different shop on Monday but sadly they seem more confused about what a posi-lok is than I.

 

First of all here's this, http://www.4x4posi-lok.com/. And second, are really pulling it back hard and quick to lock it in?

And btw , check the ujoints, a bad one can make it seem like it jumping in and out when it's really not.

 

The part I am really not clear on is what parts of the system the posi-lok replaces. Does it replace the actuator and tubes leading to it, or just the parts downstream from the actuator?

Regarding ujoints: The roads here are solid snow/ice due to salt not being allowed so it is fairly obvious when you are or are not in 4WD. I was sure I was in 4WD (despite the light not being on) and as soon as I made a left turn I heard the moderate thunk and lost most of my traction.

Edit regarding how I shift: I have tried various ways of shifting but I should note that I have never had any problems prior to getting the new pads and rotors in a couple of weeks ago, so shifting style should not matter.

 

the posi lock completely replaces all of the vaccum parts and the actualor it gives u a linkage in the cab to make sure the front axle is engaged and will stay engaged

 

Damn, that is what I was afraid of. When I asked the shop where I will drop it off Monday for diagnostics the person there thought it still required the actuator that sits off the cad.