91 Silverado 4L60e swap.

[Girthrockwel]

I bought my truck about 5 years ago and they guy that I got it from had done a 5.3L swap in it. Not the best job in the world as I’ve been fighting some electrical gremlins and the harness he used isn’t in the best shape in the world. He also kept the old 700R4 in it. He had an adapter made To mate the old tranny to the newer engine. He said it was because of a length difference and I believe maybe the splines were different.

I’d like to swap to a 4L60e as the 700 is starting to feel a little weak and if I’m going to pull it to rebuild I might as well replace it with something new. What will be involved here? Will the crossmember hit the 4L60e in the right spot? Will I need a different length driveshaft?

Thanks in advance for the help!

 

[df2x4]

Just my opinion, but I have no idea why you would do this and not go with a 4L80E. If your 5.3 is making any kind of decent power you'll roast a 4L60E just as easily as a 700R4.

 

[Girthrockwel]

Just my opinion, but I have no idea why you would do this and not go with a 4L80E. If your 5.3 is making any kind of decent power you'll roast a 4L60E just as easily as a 700R4.

That makes good sense. Are the exterior dimensions any different and what will I run into going with the 4L80E?

 

[df2x4]

That makes good sense. Are the exterior dimensions any different and what will I run into going with the 4L80E?

Exterior dimensions are a little different, the 4L80E is a few inches longer than a 4L60E or 700R4. You'll need to move the transmission crossmember back a little on the frame and find a shorter driveshaft. Otherwise you should be looking at roughly the same work load as swapping in a 4L60E. Wiring, PCM tuning, etc. The fact that you're already LS swapped should make things easier regarding the tuning, as anyone with HPTuners should be able to work with those PCMs.

I have a link to the 4L60E to 4L80E swap thread I did on my red truck in my signature. It's a '97 C1500 with the factory black box PCM (and I already had the wiring for the 4L60E) so some of the stuff in there won't apply to you, but it should at least give you an idea of what's involved.