I have a 1989 GMC 3500 7.4L but wanted to change it over to a 5.7L and a overdrive transmission to pull our camper and have better gas mileage I know that there is a 700R4 that will fit but I haven't ever had any luck with it I was wondering if they had a 4L80 transmission that I could change it to that would work in the 1989 year model?
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Can I put a 4l80 transmission in my 1989 GMC 3500 5.7L ?
- Thread starter poorboysc
- Start date
MrMarty51
Well-Known Member
Welcome to the forum PBSC.
Anything can be made to work in anything else, just depends on how much You wanna spend to get the job done.
The 4L80E will fit and work just fine behind a SBC but it will take certain components and most likely a standalone shift controller.
Others with more knowledge will jump in and give a lot more info than I can.
Anything can be made to work in anything else, just depends on how much You wanna spend to get the job done.
The 4L80E will fit and work just fine behind a SBC but it will take certain components and most likely a standalone shift controller.
Others with more knowledge will jump in and give a lot more info than I can.
MrMarty51
Well-Known Member
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By using that @ sign ahead of someones handle sends them a notice that they are being called upon.
Will L.
Well-Known Member
Welcome. So here is some things.
4l80e is a stronger transmission and will last longer, saving money in long term cost or repair and tow costs.
But the 700r4 has better od ratio so will get lower rpm on hiway and better acceleration gearing. Can not tow anywhere near as well.
So the 700r4 is better when empty but the 4l80e is better when loaded.
the 7.4 burns more gas when empty, the 5.7 is going to do ok empty, so long as you drive like a grandma. When you tow anything heavy it is going to be amazingly horrible mpg.
Also towing up hill and when trying to accelerate hard it is going to be under powered.
So it depends how often you drive empty vs towing.
There are other options, like the LS 6.0, and it can be improved by turbo. Gearing choice in differential could be an option as well.
4l80e is a stronger transmission and will last longer, saving money in long term cost or repair and tow costs.
But the 700r4 has better od ratio so will get lower rpm on hiway and better acceleration gearing. Can not tow anywhere near as well.
So the 700r4 is better when empty but the 4l80e is better when loaded.
the 7.4 burns more gas when empty, the 5.7 is going to do ok empty, so long as you drive like a grandma. When you tow anything heavy it is going to be amazingly horrible mpg.
Also towing up hill and when trying to accelerate hard it is going to be under powered.
So it depends how often you drive empty vs towing.
There are other options, like the LS 6.0, and it can be improved by turbo. Gearing choice in differential could be an option as well.
- Staff
- #5
Yes, I helped swap an 88 R3500 that came with a 5.7l from a th400 to a 4l80e a few years back for my neighbor. The hardest part for us was finding the right PCM for it and gauge cluster as I am beyond OCD about doing stuff so it can be worked on with common tools, and use off the shelf parts. So that meant finding a 7427 PCM to control the engine & trans with a 5.7l/4l80e PROM chip in it, and finding the ever allusive 90-91 electric speedo cluster(if you have a gmt400 this doesn't apply since they were all electric).
The electrical for me wasn't that bad, I repinned from the 7747 ecm plugs into the 7427 pcm plugs, added in the wiring harness down to the trans, installed a vssb, changed the knock sensor, removed the knock module, and connected up the speedo wiring. The front driveshaft had to be shortened 3.5 inches iirc, modded the crossmember since we couldn't move his back, drilled new holes for the shift linkage pivot bracket, and lengthened the shift rod.
All and all not a bad job, just time consuming. And he's beyond ecstatic with the finished product. It shifts better than the th400 ever did and he said his empty mpg's almost doubled.
The electrical for me wasn't that bad, I repinned from the 7747 ecm plugs into the 7427 pcm plugs, added in the wiring harness down to the trans, installed a vssb, changed the knock sensor, removed the knock module, and connected up the speedo wiring. The front driveshaft had to be shortened 3.5 inches iirc, modded the crossmember since we couldn't move his back, drilled new holes for the shift linkage pivot bracket, and lengthened the shift rod.
All and all not a bad job, just time consuming. And he's beyond ecstatic with the finished product. It shifts better than the th400 ever did and he said his empty mpg's almost doubled.
- Staff
- #6
Everything said about the swap, a 5.7l tbi is about gutless stock, and for what you would spend swapping over to a 5.7l from your 7.4 you could easily buy an early gen 3 lq4/4l80e pullout combo. Change your fuel pump in the tank to ep381 acdelco, cut the LS harness down, buy some dirty dingo engine mounts, and swap over to a modern LS for similar money with more HP that will get you your MPG's while still being able to tow. This would be your best bang for the buck combo. Or build a 383, BPE aluminum vortec style heads, first fuel injection TPI intake, and control it with an 0411 for an all out grunt small block combo. It's going to boil down to how much you want to sink into an old truck.