Nv3500 to 4l60e conversion?

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Lewis1129

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I have a 91 2wd scsb. It was born with a 5spd which I prefer, but my wife doesn't like driving it and wants me to put an auto in it. I would like to go 4l60e, but know that the 700r4 would be a lot simpler. I plan to do an ls swap in this truck as soon as it's financially feasible. What would be my best option on transmission and what all would I need parts wise to do this swap.
 

df2x4

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"Best" transmission really boils down to what you want and how much work you're willing to do for it. Like you said, the 700R4 would be easiest and cheapest by far as it doesn't require any electronic control. A 4L60E or 4L80E (The 80 would be my choice) will require a stand alone transmission controller to work with your current setup, and those are usually pretty pricey.
 

someotherguy

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Yeah, you'd practically need to find a donor truck to get all the parts to do a 4L60E conversion without it destroying you nickel-and-dime style, and it would have to be a 1993-1994 only, with same engine you've got, so you could use the engine harness and PCM from the donor.

You're definitely right that 700R4 (4L60) would be the way to go since you're a '91. You'd still need to setup the torque converter lockup control; to be perfectly honest I've never looked into it enough to know what's needed. Probably the engine side wiring harness so you'd have the minimal amount of wiring to it (or dig hard into factory wiring diagrams to do it yourself) and I'd guess the automatic compatible ECM or at least the memcal from the ECM. Again obviously you'd want to stick to same engine and very close to same year.

The only appreciable difference between a 700R4 (4L60) and the 4L60E would be the electronic control; you don't really gain anything on a daily driver by the extra work of going to the 4L60E. It has some advantage to a person wanting to do custom tuning as they can have better control over it through tuning. Otherwise the transmissions are from the same family and are close enough mechanically that it's not like one is stronger than the other; they're both light duty automatics.

I say go 700R4 and just be sure you really, really read up on proper adjustment of the throttle valve cable so you don't roast it right away. Totally critical to the behavior and lifespan of the transmission.

Richard
 

someotherguy

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Parts wise you'd need the transmission (1988-1992) and if you get it from a 1988-1990 that isn't a pickup but an SUV be sure it has the electronic speed sensor in the tailshaft housing, vs. a cable speedometer output; the first TBI-equipped squarebodies change year by year on that stuff.

You'd need the converter and flywheel, of course. Be sure to remove the pilot bushing/bearing from the end of your crankshaft as it can/will interfere with proper seating of the torque converter.

Don't forget the dipstick tube and bracket.

You'll need a throttle valve cable; get the one from the donor truck but consider buying a new one and using the original as an example to be sure you got the right one.

Here's a tricky one: some manual trans-equipped TBI trucks don't have the stud on the throttle arm for you to attach the throttle valve cable, so check yours closely. You could either swap out the throttle body - 1991-1992 to get the one with the correct TPS style for your 1991 harness; some 1993-1995 will also not have the TV cable stud since they went electronic.

As I mentioned earlier the engine harness could be helpful for the torque converter lockup, but that would have to come from a 1991-1992 to be a direct fit onto your truck; 1988-1990 would also work but the firewall retainer block is shaped different. And ECM/memcal.

Really going off fuzzy memory and not enough sleep so anyone please feel free to elaborate or correct me.

Richard
 

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Whatever the question, buying another GMT400 is allways the answer.

Buy a second truck with an auto for the wife, or make up a story about how having a manual is the core of your being, how having a manual makes you a man amongst boys, etc. and teach her how to drive it better.

I must be a shallow individual, because if I only had one truck and I was told to auto swap it, I would have my lawyer contact hers. :) Pretty sure auto swapping a manual pickup is a crime in some states. :)
 
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