Can the 4L80 cross member be used for the 6L80? I don't have the 4L60 cross member anymore, and I can't find anyone that makes a 6L80 cross member. for the gen-4 fbody.

 

I imagine you could just modify the one you have. It’s been awhile since I did the conversion. I believe I went with a QA1 rear torque arm relocation bracket (steel bar that bolts to rear differential and transmission) which also allowed me to set pinion angle. It is a good product it fit perfect and I was happy with it.
sorry meant to reply this to the previous post (utinator)

 

I got under my car and took a few measurements this afternoon. My current 4L80e appears to have the cross-member attachment holes about 2-3 inches further aft than the 6L80. I measured from the back of the engine block, to the center of the trans-crossmember bolt holes on the 4L80. Then, I measured the 6L80 from the front of the bell housing, to the center of the cross-member bolt holes. It's difficult to get an accurate measurement, due to it not being a straight line. Anyway, it looks like my 4L80 cross-member will need to go about 2-3 inches forward before I could use it on the 6L80.

Would the 4L60 cross-member be closer to lining up with the 6L80? What about the T-56 cross-member? I only have a BMR 4L80 cross-member. I don't have any other cross-members to compare it to.

 

I think the 4l60 bracket lined up quit well on the 6l80. Been awhile but I think it lines right up but the torque arm does not. If I remember correctly I cut that off temporarily altered it and ultimately got a new relocation bracket and torque arm for the rear end from I wanna say BMR or QA1.

 

Can you elaborate on this a little more? HOW do you "tie them in". Pics would be awesome. Zero Gravity sent me 2 wire diagrams for my car/PCM, and 1 wire diagram for the TCM wire harness. There are absolutely no instructions on HOW or WHERE to connect/splice the wires. The big plastic connectors are obvious. You can't mess that up. I just need to figure out how and where to splice the wires where they need to go.

 

I started a build thread in case anyone wants to follow along. Opinions and advise would be greatly appreciated.

https://ls1tech.com/forums/automatic...6l80-swap.html

 

Yes, the 4L80 cross-member can be used. No, it doesn't just bolt right up . It needs some cutting and welding to work. The 6L80 shifter bracket also has to be cut and welded to fit properly. The 4L80 shifter bracket doesn't even come close to attaching to the 6L80. See my build thread (link above) for details.