C30 heavy duty rear axle top speed

[special-K]

I would leave that original rear in place and add an auxiliary transmission. You would not have to alter your PTO set-up, you would be leaving that truck as the cool not too common 11k# axle option that it is, and be doing what an innovative minded truck owner might have done back in the day. There was a company called Brownie that made units for this application and I know of guys doing their own engineering to install back to back transmissions. Twin sticking is just too dang cool and a totally vintage truckin' way to go. These days you could simply (other than the $1,600 cost) install an Advance Adapters Ranger 2spd. With an auxiliary transmission you will also have the ability to split shift, but would not have to if you didn't want. I believe you will gain a higher speed overdrive over using an overdrive transmission.

https://www.advanceadapters.com/cate...-splitter/236/