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Video: How to Mount an LS Engine to an Older GM Transmission

There are a lot of factors to consider when swapping an LS engine into a vehicle not originally equipped with one, perhaps the most important being the transmission choice.

The good news is that GM made it really easy for folks to mount an earlier transmission to an LS: the bellhousing patterns are virtually identical and there are no unusual offsets to resolve.

That means you have a ton of options when it comes to mounting a transmission to your LS, including the TH350/400, Muncie, Saginaw, and 700R4/4L60E—heck, even a Powerglide will bolt-up without any significant fabrication.

But, there are a few parts you’ll need to buy and install to ensure your transmission will work properly behind a GM LS engine.

This video shot by the folks over at Summit Racing will go over exactly what it takes to mount an older GM transmission to an LS, including a list of part numbers. Automatic transmissions will need a thicker (or bell-shaped) flexplate and adapter/spacer, while manual transmissions will need a new flywheel with an extended clutch mating surface flange and pilot bushing.

This video is a must-watch if you’re starting an LS swap project, particularly if you haven’t decided on a transmission yet.

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4 Comments

  1. is there a way to use the kickdown on a TH350?

    • OnAllCylinders Staff says:

      Hey Billy, Lokar makes the brackets and cables for an LS1/TH350 combo, for both carbureted and EFI applications. If you’re using a drive-by-wire throttle body however, you’ll have no choice but to omit the kickdown cable and put the transmission into second gear manually.
      If you’ve got specific questions on your setup, give the technical department at Summit Racing a call, 330-630-0240. They’ll be able to point you in the right direction.

  2. Mike friendshuh says:

    Hello summit racing. My name is mike and I have a couple of questions about my swap. I am putting a 5.3 out of an 02 2wd Yukon into my 90 Chevy 1/2 ton. My truck has a TH350, so I am planning on getting the spacer, and ovaling the mounting holes. I was planning on reworking the harness myself, maybe, attempting to anyways.
    My 5.3 is DBW, and all I can find is that I need a manual valve body for the TH350 and I will have to shift through the gears myself. Any info I can get on what to do with the transmission plug on the harness, and if there is any way to make it an automatic transmission would be very helpful.
    Thank you.

  3. I have a 2005 5.3 truck motor& flywheel from automatic what is needed to mate to 97 Silverado 4l60e trans

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