4l80e and NP203

[rwljpl]

How hard is it to match a 4L80 with a NP203 t case?

 

[rwljpl]

I should add - I am replacing a TH350 transmission

 

[Vbb199]

Well, most 203s are 32 spline, and there's a rare few who are 10 spline (behind a 4 speed)
The 4L80e is 32 spline.

I'm assuming since a th400 was paired with a 203 from the factory, a 203 should be able to mate up to your 4L80e



Keep in mind your vss for your 4L80e will need added if there's a 203 back there

 

[nvrenuf]

You'll need to research the trans tailshaft lengths, the 400/203 combo uses an exceptionally short trans tailshaft. If I remember correctly, the 400 tailshaft sticks out of the case about 1".

If you're currently using a 350/203 you have a lot to change -

- The 203 will have a 27 spline input, you need a 32.
- Your current adapter will not work, the 350 has a 4 bolt pattern where the 400 / 4l80e use 6.
- The 400/203 adapter may work but I think it uses a gasket where the 4l80e uses an o-ring so some minor machine work may need to be done to the adapter.
- As stated, you'll need to figure out the VSS signal for the trans, I think Autometer makes stuff for this.
- The 4l80e is electronic so you'll need an aftermarket controller or full manual valve body for it.

 

[Bextreme04]

Its a pain and you will need a lot to make it work. You would be better off just finding an 85-later NP208. Its a stronger transfer case and lighter as well. You also can't just use a TH400/203 adapter. The 4l80e index ring is smaller than the TH400, so it won't fit. You either have to have .1" diameter milled off the index ring, or you need to have something like this https://northwestfab.com/products/gm-4l80e-to-th400-np205-adapter-spacer-kit

 

[rwljpl]

Guys thanks for all this info
I did think about changing the t case along with the trans but it just keeps getting more complex and expensive
Thankfully I found a 700r4 to use instead - no electronics, should hook up to the 203 pretty easily, and much simpler overall
700r4s are getting much harder to find so I was about to give up

 

[Vbb199]

4L80e and 203 to a 700r4 and a 208, my what a jump

 

[Bextreme04]

Yeah, but way simpler to swap a TH350 for a 700R4 than it is to change everything out. The overall length will still be changed though, so be prepared for driveshaft changes