question on 77-87 K2500

[mark_k]

Kickin around the idea of buying a 77-87 2500 and dropping in a 6.6. I have a couple of questions regarding this idea. Wanting to keep the straight axle. What would the best option trans wise be? Should I keep the Allison and set it up with a divorced tcase since I dont believe the factory case would bolt up. Or would I be better to find a trans that the factory tcase bolts up to and just use that instead? Also is there a company that makes custom pcm's? Or is this just a stupid idea that would be dang near impossible? Main use would just be a weekend driver. Thanks

[MikeNH]

The Allison is a very large transmission. I don't know that it would fit without at least a body lift. That aside, anything is possible. Time and money like any other big undertaking.

[mark_k]

I was planning on doing a 6 or 8 inch suspension lift. What would be a good option for a trans that would hold up to the 6.6? Thanks

[Chris]

The Allison would be best, but a body lift may be needed to fit the trans. 250HD's after 01 use a 2" to fit the Allison

[mark_k]

Ok, prolly make it look better too.With using the Allison, Ill have to divorce the tcase correct, or does anyone make a spline adapter? Thanks

[Chris]

Most likely will need the transfer case from a donor

 

Sent from my Samsung Galaxy S4 using Tapatalk 4

 

 

[mark_k]

Donor as in the one with the allison, or one from a 77-87? Thanks

[Chris]

Allison. most likely from a work truck model with floor shift case

[mark_k]

Thanks, wasn't thinking when I asked that. I was looking , the front output shaft is on the right side correct? With the differental being on the left side of the truck will it work, or will I need to swap to a ford front? Thanks

[Chris]

That is where my knowledge runs out.

[mark_k]

Ok, thank you.

[Larry]

Thanks, wasn't thinking when I asked that. I was looking , the front output shaft is on the right side correct? With the differental being on the left side of the truck will it work, or will I need to swap to a ford front? Thanks

 

Yes, if you chose to use the factory manual shift NV271 transfercase behind an Allison with the LH front output you would need to swap in a LH drop front axle from an older Ford. The other option would be to be creative with the transfercase. For the last 28 years all fullsize trucks have used an industry standard SAE 6 bolt round transfercase to transmission flange adapter. This means any 1985 or later tcase will bolt on to the Allison but the trans output shaft size and spline count won’t match any older RH output tcases. I’ve seen a guy on another forum take the input gear out of a late model 271 and make it work in an older 241 with the RH front output. It was ingenious! His concoction was an 8.1L/Allison in a 73-87 square body truck.

 

I installed an 8.1L in my ’78 K10 about 5 years ago but run a NV4500 5 speed behind it with a NP205. I've got about 30,000 miles on it since the swap and just love it! Even with you wanting to go the route of a Duramax you could still go that route as well. NV4500’s can handle a Duramax and bolting one to a Duramax would be no problem. They all use the same bellhousing design. NV4500’s were used behind many of Cummins Dodges. Personally, I wouldn’t

even consider a Duramax for any swap. Decent engines but when they break, THEY are BROKE and so will you be. Ever see how much it costs to replace a set of injectors in a Duramax? You can buy a lot of gas for what it takes to maintain a late model diesel. That is the reason I went with the 8.1L. It has diesel like torque without all the BS of owning a diesel.

 

This is my 8.1L/NV4500 beast. It weighs 8,000 lbs. when loaded for an outdoor adventure trip and delivers 11 to 13 MPG. That is not too bad for a heavy old truck with the aerodynamics of a drive in movie theater screen.

 

 

 

[kstruckcountry]

Sweet truck Larry.

 

But OP, I can guarantee you it's easier to put a solid axle under a Duramax than put a Duramax into an old truck.