4L80E 4wd Swap

[66gmcguy]

Hey all. I'm trying to figure out how to do a 4L80E swap in my 1982 K2500. It's currently got a 350/SM465/NP208 combo and I just can't live with the SM465 anymore. I was originally thinking of getting an NV4500 but since this thing is my daily, I'd rather go back to an automatic. Having O/D is a must, and I don't want to use a 700r4 because of sensitive throttle valve adjustment, so a 4L80E is really my only option. I realize that I need a VSS output on the T/case, so ideally, I would get a NP241C from a 91 suburban, but as predicted, those are nearly impossible to find. In fact, the only NP241C that has VSS I've found is a 27 spline output (I need 32) but the guy wants $1000 for it, and it needs a complete rebuild. I did find a guy who's got a NP241C on the back of a SM465 he wants to sell, but it has a cable drive output. Is there any way to convert it to a VSS? Would parts from a newer driver drop NP241 swap into this unit? Or am I SOL until I find the exact transfer case I need? I'm open to any ideas on how to get a good, reliable VSS output for the transmission controller, even if it means converting the NP208 I have, if that's even possible.

[kwmech]

You do not really need the VSS on the T-case. When the 4l80e is built have them put in the output sensor that you would use in the 2wd trans. Probably you'll be 2wd mode 95%+ of the time anyways. This way you can still use the cable off the t-case for your speedo. You're going to need a stand alone controller so talk to them about the programming and how it will affect the shifting going this direction. The t-case----buy the 27 spline input and rebuild it with a 32 spl INPUT. And now would be a good time to put a slip yoke eliminator into it at the same time. That is the way I went with my Suburban when I converted to a 4l80. I just about ended up with a 1000 dollar t-case with all the parts needed. If you can I would snag the cable case. the cable case was 1 year only --1989

[66gmcguy]

Originally Posted by kwmech

You do not really need the VSS on the T-case. When the 4l80e is built have them put in the output sensor that you would use in the 2wd trans. Probably you'll be 2wd mode 95%+ of the time anyways. This way you can still use the cable off the t-case for your speedo. You're going to need a stand alone controller so talk to them about the programming and how it will affect the shifting going this direction. The t-case----buy the 27 spline input and rebuild it with a 32 spl INPUT. And now would be a good time to put a slip yoke eliminator into it at the same time. That is the way I went with my Suburban when I converted to a 4l80. I just about ended up with a 1000 dollar t-case with all the parts needed. If you can I would snag the cable case. the cable case was 1 year only --1989

I was thinking about that. You're correct, it's mostly a pavement truck but even when I'm offroading, I'm in 4H, and if I ever shift into 4L, I almost always stay in first gear. However, I am curious if I could use a reluctor ring (or the whole output shaft with the ring if need be) and the output housing with a VSS port from a newer driver drop 241 from the GMT400 trucks on the older passenger drop 241.

[kwmech]

Probably the tone ring and sensor but the aluminum housing is different. If you contact Off Road Design I'm sure they'll swap it out for you

[66gmcguy]

Originally Posted by kwmech

Probably the tone ring and sensor but the aluminum housing is different. If you contact Off Road Design I'm sure they'll swap it out for you

thanks for the info. this guy wants $250 for the cable drive 241. is that a good price?

[kwmech]

Originally Posted by 66gmcguy

thanks for the info. this guy wants $250 for the cable drive 241. is that a good price?

Yes it is, if you don't take it, I will for extra parts

[THI]

1990 & 1991 NP241C's from a K5 Blazer or Suburban will have the VSS. $200 - $250 is the going core price in my area for those. 1989 was the one-year only NP241C pass drop with a mechanical gear for the speedometer. NP208 and NP241 use the same adapter and you will need the TH400 adapter for those to mate to the 4L80E

[66gmcguy]

Thanks for all the responses. I ended up keeping my NP208 but I found a dodge NP208 with a fixed rear yoke. I’m gonna attempt to splice the back half of the dodge case onto the front of the Chevy case to get the fixed yoke. That 241 is 5.5 hours away from me one way. I may go get it still though, assuming I can find an entire day to go there.

[kwmech]

I thought your 208 was 27 spline input? A 241 is a little bit stronger. But if you need a 32 spline 208 I have one in my garage I'd let go for about 200.00

[66gmcguy]

Originally Posted by kwmech

I thought your 208 was 27 spline input? A 241 is a little bit stronger. But if you need a 32 spline 208 I have one in my garage I'd let go for about 200.00

No I have a 32 spline 208. My truck had a TH400 in it originally.

[72k20Farmtruck]

I did this a few years ago in my 82 K20 pickup, got a vortec 454 and 4l80e out of a 99 suburban and bought a howell engine harness and ecu for it. With the 4wd, we bought a reluctor ring and we were able to install it on the tailshaft of the 208 tcase, and had our machinist buddy machine a hole for the sensor in the tailhousing. I’ll get the part number for the reluctor ring tonight for you. And i can provide some pictures too. Hope this helps.