Converting a transmission to "LL"


Active member
Does anyone know if you can add LL or deep reduction to an eaton 9 or 10 speed? We have mostly 8LL and one 9LL in our trucks and the low hole is very useful for what we do. My thought was that if the conversion is do-able, we would convert the others if the tranny ever has to come out for other reasons, or if it doesn't have to come out maybe do it anyway. I was thinking it could be as simple as adding a back box, plumbing a few airlines and shortening the drive shaft? Or maybe not?


New member
I'm not as versed in the 8LL and 9LL worlds as I am in the 13 and 18, but the short answer i believe would be no. As for converting 13's to 18's, or 9's to 13's and 18's, in the older models (I believe mid 80's and older) it was possible to simply change a rear box to change the layout of the trans, however in newer models the gear ratios will not line up, it will be about impossible to shift. As I said, I'm not as familiar with the LL models, but seeing as how they are built like a 13 or 18, only using a deep reduction instead of a splitter, then no it would not work.

Truck Shop

Well-known member
In the low torque transmissions you could convert a 9spA to a 13sp, but not a 9spB. And your right you cannot convert the later high torque transmissions.

Truck Shop