Transmission

[Supercharged111]

No conversion u-joint, you need to get the driveshaft shortened. No cross member mods, just drill the frame if needed. Some frames are drilled both ways. I want to point out that you don't get that bog on an upshift with the 4L80E since the gears are closer together. That and the small block converter on a 4L80 is looser than the 4L60 piece. OD does pull better and 3rd feels the same as 4L60. 1st and 2nd are noticeably taller. Since you lose less on an upshift, you also don't get as much of a jump on a downshift.

 

[stutaeng]

Ditto on the closer gear sets on the 80. And I had forgotten some of the GMT400 frames had the extra set of holes already there.

As for the driveshaft, I thought the 2-piece with the middle slip yoke didn't require the driveshaft getting shortened? But the yoke on the 80 is a much beefier 32 spline? vs 27 spline of the 60. I'm pretty sure something needs to get converted over. Or custom made.

 

[df2x4]

As for the driveshaft, I thought the 2-piece with the middle slip yoke didn't require the driveshaft getting shortened? But the yoke on the 80 is a much beefier 32 spline? vs 27 spline of the 60. I'm pretty sure something needs to get converted over. Or custom made.

Disclaimer, I let my mechanic handle this part of my swap... But from what I remember in my red truck ('97 C1500 4.3L RCLB) I was able to switch from a one piece aluminum driveshaft to a two piece steel unit from a heavier duty GMT400. It's been a while but if I recall correctly the two piece shaft was set up for a 14 bolt, so we used a 1350-1310 conversion U-joint to connect that to my factory 10 bolt.

My donor 4L80E came with a bolt on yoke instead of a slip yoke, so that's how the front half is connected.

 

[Supercharged111]

Ditto on the closer gear sets on the 80. And I had forgotten some of the GMT400 frames had the extra set of holes already there.

As for the driveshaft, I thought the 2-piece with the middle slip yoke didn't require the driveshaft getting shortened? But the yoke on the 80 is a much beefier 32 spline? vs 27 spline of the 60. I'm pretty sure something needs to get converted over. Or custom made.

Mine was a 1 piece. My wheelbase with a 4L80 is rare as hen's tereth so I wasn't going to find a bolt in option. Also, you:ll need to ghetto grind the front driveshaft to get it to stretch out long enough, unless you want to swap in a 9.5" front diff while you're at it.

 

[stutaeng]

Disclaimer, I let my mechanic handle this part of my swap... But from what I remember in my red truck ('97 C1500 4.3L RCLB) I was able to switch from a one piece aluminum driveshaft to a two piece steel unit from a heavier duty GMT400. It's been a while but if I recall correctly the two piece shaft was set up for a 14 bolt, so we used a 1350-1310 conversion U-joint to connect that to my factory 10 bolt.

My donor 4L80E came with a bolt on yoke instead of a slip yoke, so that's how the front half is connected.

Yup, that's what I was thinking about. On my 1500 NBS I'm doing the 4L80e swap, I had bought that u joint, but my slip yoke I got was too long, so I returned both. I did find the right yoke though. I haven't gotten to the u joint part yet...