transmisson

If the trans is a conventional column shift, then you have the 1000, if it is a pushbutton shift, then it is the 2100..

Get the number off the trans and call Allison, they are very helpful.

Go here and register your WH chassis and the print-out will tell you about all of your major systems. Workhorse registration

Thanks guys very helpful

To do the Allison correctly you need to change it to Transend (SP) Synthetic. Do a search on this forum, and IRV2.com, for "Allison fluids change". The step by step is to drain, change filter, fill, drive it 25 miles, then change fluid & filter again. Very costly but the only way to get all the old fluid changed.
Don

Since it has Transend Synthetic in it already, Would I need to change it twice?
According to the files I have on it it already had trasend in it, I am changing because it sat so much.

If it already has Transend, the two time flush probably is not necessary, The one time change might not be necessary. What ever makes you feel comfortable. I might just change the spin on filter, its pretty much a sealed environment in the transmission..
Donnt forget to go have fun.

Transsyn still has to be changed on the regular schedule after the first time it was switched, then it's good for the extended service mileage on that service. I was told this on my 3000 Allison.