Hi, I have a 1999 Ford F800 dump truck with the Cummins 24V and Allison AT545 auto. It has plenty of power once rolling, my problem is starting off, especially if the ground is somewhat soft or if I'm stopped at an embankment like a RR crossing etc. I think it has Rockwell rears and I was wondering if it would be possible to swap the single speed rear to a 2-speed.

 

Yes it's possible but it wouldn't be anything like shifting a 2 spd axle with a manual trans.
You would have put the trans in neutral and shift the axle into low range before starting off, once you get rolling and were ready to shift the axle you would have to shift the trans shifter to hold it in that gear, let up on the throttle while shifting the 2 spd axle and then reapply the throttle, then place the shifter into high gear.
Best case would be to start off in low axle, let the trans shift up to it's highest gear, then let up on the throttle and shift the axle to high range.
2nd choice would be to start off in low axle while holding the trans in low gear, once your moving let up on the throttle while shifting to high axle, then reapply the throttle and move the shifter to high gear.
You do not want the trans shifting at the same time the axle shifts, it'll get ugly when that happens.
Trucks that came with 2 spd axles have a device to keep the speedometer accurate in ether axle range, your truck won't have this so your speedo will show fast while in low range.

Your truck must have been a municipal owned truck having the smaller 24v engine and Allison AT545, these are normally found in lighter chassis and school busses.
My F800 has a 8.3 Cummins and Allison MD3060 trans.

 

I don't need split ranges, just a low for when I get into tight places, I figured I'd just wait until I got into high (4th) to upshift the axle and do just like you said... Anyway, you answered my question. Thanks!

 

Find out what you existing ratio is. Post a picture of your warranty plate with the axle codes.

 

I'll take a wire brush and clean this up if needed.

 

Doesn't that first picture show "Ratio 411"?

Looks like you have a 17,000lb axle. It also appears there are two speeds with a 4.10/5.72 ratio set.

You will have to do some calling and searching and measuring etc to find one, but it appears it could be done.

http://partsmanuals.org/rockwellpart...rts-Manual.pdf


What tire are you running?

 

Yes, and low pro 22.5

 

Well, there goes the "use a shorter tire" suggestion.

So many axles, so few of what your want:

https://www.mylittlesalesman.com/199...ousing-8970443

 

Going to start a new thread regarding this but if I could get full throttle from the get go instead of being limited to 1500 RPM until the engine/transmission senses that I'm moving, I probably wouldn't need the swap.

 

I know it's an older thread, but I don't think adding a 2-speed axle is going to be easy. In part because you'll have to figure out the electronics to the speedometer because they shift with the axle. If I were you I'd dump that awful AT transmission and put in an MT-series. You will get better gearing and lockup which will improve your freeway speed by several MPH on the top end as well as saving you fuel.