Utilizing A Transmission That Isn’t Designed For An LS Power Plant

When performing an LS swap, issues come up all of the time. Whether it’s wiring, building a proper fuel system, or tuning, people always have questions. Another frequent subject when it comes to swapping in an LS is connecting an automatic transmission that was not specific to the LS platform. While this seems like it wouldn’t be a big deal to figure out, things tend to get tricky with all of the different options.

Recently we swapped in a 5.3-liter LS into a 1991 Suburban. Initially, we were planning on running the factory 700R4 transmission behind the new power plant. After some consideration, we felt it necessary to go with the much more robust 4L80E. You would think that the modern transmission would work with the 5.3 with no problem because it came off of an LS engine. However, you would be mistaken. The transmission will bolt up without any issues, but the torque converter location is too far back to center in the crank hub.

So, why will the 4L80E not work? An LS engine is an LS engine and all of the parts interchange. Right?

To answer this question, we checked with ICT Billet after stumbling on an excellent diagram that shows the problem. The 1999-2000 6.0-liter engines used a long crankshaft that extends .55-inches past the lip of the rear cover. A standard crankshaft, like the 5.3-liter engines use, projects out only .13-inches from the same lip. While the 2001 and up 6.0-liter engines went to a standard length crankshaft, GM used a crankshaft spacer (PN 12563532), in between the crank and the flexplate to move it out. So basically, the 4l80E was designed to work on an engine with a long crankshaft.

In order to mate the 5.3 to the 4L80 transmission, we needed PN 551356X, which is a PRW dished flexplate that is SFI 29.1 certified and includes the bolts. We also ordered the converter hub flexplate crankshaft adapter PN 551165. This hub extends out to where a long 6.0-liter crankshaft would be and allows the 4L80e torque converter to center itself in the flywheel. This part will alleviate any movement or vibration with the converter while accelerating or decelerating, avoiding transmission damage.

While these parts work with our 5.3/4L80 combination, they also work with a TH400, TH350, 700R4, and 200R4 bolted to an LS.

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About the author

Brian Havins

A gearhead for life, Brian is obsessed with all things fast. Banging gears, turning wrenches, and praying while spraying are just a few of his favorite things.
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