Author Topic: LS swap transmission question  (Read 395 times)

Offline Kl7293

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LS swap transmission question
« on: January 16, 2018, 06:16:00 AM »
I have a 1978 Chevy truck 4wd automatic. I want to do a LS swap but I am unsure about what route to do for a transmission. The stock trans is a 350 with no overdrive. Thanks for any help.

Offline smurfasaur

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Re: LS swap transmission question
« Reply #1 on: January 16, 2018, 08:52:57 AM »
Easiest route for sure is to keep the th350. Lots of people go that route with good success. But if you want to really improve your fuel economy you will definitely want an overdrive trans.

The 4l60e (basically an electronically controlled 700r4) and 4l80e are both electronically controlled and came behind many variations of lsxís, and lots of people swap those in as well. If you get an engine/trans pullout out of a pickup or something the nice thing is the stock PCM can be used to control the engine and the trans. Itís not a huge deal to swap in the 60e or the 80e usually, the biggest things you have to deal with is the VSS (vehicle speed sensor), and making sure the trans bolts up to your existing transfer case (or swap in a pullout engine trans and tcase).

It all depends on what your goals for the truck are and what level of fuel economy youíre willing to accept. Iíve heard of people getting 15-16 mpg out of a 5.3 swap with a th350 or 400, but Iíve heard of as much as 18-20 out of a 5.3/overdrive. Iím building my truck to be a DD that I can drive across the state to go hunting, so I went with a 4l60e but thereís nothing wrong with keeping a 350, especially if itís in good shape and you will just be driving around town.


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Offline Kl7293

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Re: LS swap transmission question
« Reply #2 on: January 16, 2018, 09:57:54 AM »
Surely would like to have the overdrive. The truck will be used primarily as a weekend toy, but would also be used to tow the boat a few hours on occasion. But I would also prefer a smooth swap and from what I have researched. The transmission/transfer case match up can be difficult. Possibly could find an older 700 that would bolt directly to my existing transfer case. Thanks for the response.

Offline smurfasaur

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Re: LS swap transmission question
« Reply #3 on: January 16, 2018, 10:24:32 AM »
Depends on what tcase you have, the 4l60e and 700r4 have the same bolt pattern (I think the 80e is the same as well) so those are really 6 to one half dozen as far as swapping in. The only other thing is to make sure you know what spline count you have on the input gear of your tcase and match it up to the output shaft of the tranny.

Thatís where I goofed up, I went from a tired sm465 to a 4l60e and didnít realize the output shafts were different (the internet told me they were supposed to both be the same... They werenít) so I had to swap the input gear on my NP208 to a smaller one but that was actually a piece of cake.


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Offline Kl7293

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Re: LS swap transmission question
« Reply #4 on: January 16, 2018, 10:34:02 AM »
My truck is factory full time 4wd....203 transfer case. So Iím assuming the 4l60e will bolt directly to my transfer case.

Offline smurfasaur

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Re: LS swap transmission question
« Reply #5 on: January 16, 2018, 11:35:11 AM »
Hmm I donít think the 4l60 will bolt up to a 203 without some work... I want to say you have to get an adapter plate of some sort or drill the right bolt pattern into the face of the tcase but I could be wrong.


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Offline Kl7293

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Re: LS swap transmission question
« Reply #6 on: January 16, 2018, 11:41:01 AM »
Ok. I will keep researching. Thanks again for the help.

Offline smurfasaur

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Re: LS swap transmission question
« Reply #7 on: January 16, 2018, 12:01:00 PM »
No worries amigo, good luck to you! Lots of good info on here if you need help with your swap.


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