This is a strange one - I dropped my pickup off at a local shop a week ago to get the tranny flushed. While they were down there, they changed one line with a pinhole, and a power steering hose that was weeping. When I picked it up Friday after work, I noticed a rumble, and the "FWD" light was on, in 2-hi. So I stopped, and shifted it to 4-hi - and the light went out! I could spin the back wheels, so it definitely wasn't in 4. I can go back to 2-hi, and the transfer case shifts out, but the 4wd light comes on and the axle locks back up (you can feel it on the road)!! So I went to 4-lo, and sure enough, the light goes OUT and it's in 2wd.
So - The question is - what did they unhook and hook back up backwards?? I'd like to take it back to the guy and tell him to figure it out himself, but it snowed here this weekend, and I'm not sure I can get it back to the shop in 2wd......
I diffedently wouldn't be driving a Cummins around in snow with only 2wd. It sucks, I know. Who knows what the guy could have done. You still clearly have a issue w/ vaccum, but that's not saying it's your only issue.
However. There is a easy rememdy for this to make sure it never happens again.
Consider the following:
A. If you got 30 spline axle shafts which were found in many 98's and some 99's. You can get by w/ just replacing the long shaft w/ a upgraded chrom moly shaft. EMS sells this @ Ebay for $335.00
B. If you got a 00-02. You can hunt down a 32 Spline big shaft from a 2002, kind of hard to come by, however the ones I have come have only ran $50.00
C. Upgrade to 35 Splines (And locate a carrier). Chrom Moly 35 shafts run 585$. EMS gots this covered again for the 94-99 model years, while Dynotrac gots the 00-02 model years covered. Both exactly $585 which is a steal if you compare to other Dana 60 chrom moly shaft kits.
"C" can be taken a step farther if you want to convert your unit bearings to lock outs. But then you are getting over $2,000.
D. Lock your shift fork in the locked position or find a way to manually control it via cable or electric.
My theory on the matter is: You bought a 4x4, it's time to make it reliable. The CAD is without a doubt, the biggest cause of 4x4 malufunction in these. OEM fixes just repair vacuum lines, which in time will always root.