[char1355]

I was wondering the same thing. Normally, the 6x6 function is controlled by the transfer case, not the transmission. From what I read, the front and middle axles are powered off the transfer case in a full time 4x4 mode. The third axle is powered off a PTO on the transfer case. So changing transmission shouldn't affect anything. These are not super heavy duty trucks. Gross vehicle weight is 5500-5600 K. An F450 pickup is rated at 14000 lbs (6350K).

 

[char1355]

6x6 transfer cases are out there, but most are big and heavy units for heavy duty trucks. Here's an article you might find interesting. It's form some strange place called Australia. LOL. https://oka4wd.com/forum/oka-maintenance/1468-6wd-np205 Another option could be to run 2 transfer cases, one in normal position and the second in reversed position. That way you could run 2wd,4wd (1 rear axle + the front), 4wd (both rear axles only), and 6wd (all axles), and you could have high and low range in some modes.

 

[char1355]

Yeah Ed, that creature is typically British. Weird. Don't know why they would build the transmission and transfer case in one piece but they did. American military trucks in the Korean War era had a NP200 4x4 transfer case but those things don't like any speed over 45 MPH or they will overheat. Those have a second rear output that could be used for 6x6 but it's not the strongest unit around. There were NP201 and NP202 that were stronger and has PTO output ports. And of course the NP205 was the last child in that list which is ultra strong and could be converted to 6x6 as was shown in that article. Only issue there is there is not switching between 2 and 4 rear. If you use a NP205 that would do 1 rear and front. A second unit of some type mounted in reverse position could do the second rear. You'd even have a host of gear ratios. for the rear section. There would be 2H, 2L, 4H, 4L, and 4 double L. 6x6 would be restricted to 6H and 6L. Would keep the brain active as to what gear the transfer cases are in. You know, there's a point here I may be wrong on because I'm not sure with way the shafts would be turning with the second transfer case reversed. That would be something to mock up before install to see if it functions correctly. Don't want to dive into an empty swimming pool.