I have a 2004 Chevy 2500hd 8.1 allison. The truck goes into 4 wheel high but when I push the 4 wheel low button, the light blinks for a minute then goes back to 4 wheel high. Any suggestions.

Thanks for any help

 

i have a 2002 2500HD also w/ the 8.1 and allison. when you push the button to go into 4 low, make sure you are in neutral, in order for four low to fully engage, you must first put the truck in reverse and go backwards for a foot or two, then put in drive and you should be good to go. let me know how it goes.

 

The going backwards thing is for the front diff to lock in, it has nothing to do with the transfer case. Just to clerify.

Shifting into 4L you will need to have the truck under 2 MPH and be in neutral. (4L is not shift on the fly)

 

Those switches are known to go bad as well.
Man 2 back to back 8.1 trucks. I am jealous! I had a nice one but sold it and now even though my 6.0 gets the job done (I really don't pull anything bigger than a 3500 pound boat) I really miss that power and that b@d@ss Allison!!!!! I can't find a decent one around here that doesn't either A: Have 250,000 miles or B: They want a small fortune for. The last one I had I bought with 120,000 miles but it was CLEAN! I gave $7500 for it. I guy offered me $8500 after I had it for a month so I let it go thinking I would find another one. MISTAKE!

 

i work in a tranny shop in new hapshire and its a commen problem its either the vacume switch on th t-case or the t-case it self both happen often, try replacing the switch if thats not it then have your truck scanned for t-case codes and diegnose the problem from there.

 

Thanks for all the information, the problems seems to have gone away. And yes Mr Shamrock, I love the 8.1 power with the Allison. I will never part with the truck. I can not believe that Chevy won't come out with another big motor for their trucks soon.