4l65e and NP203

[rwljpl]

I’m looking at swapping out the TH350 3 speed in my truck for a 4L65e. Transfer case is NP203. Is it possible to make this work? What are the challenges going to be?

 

[Vbb199]

4L65e is pretty identical to a 4L60e except a few internal things. What I dunno is, if its 27 spline or 31 spline output.

I think it is 27 spline, and your 203 is 31 spline.

As mentioned in another posting, a np208, np241, and some np205's are 27 spline.

 

[Bextreme04]

4L65e is pretty identical to a 4L60e except a few internal things. What I dunno is, if its 27 spline or 31 spline output.

I think it is 27 spline, and your 203 is 31 spline.

As mentioned in another posting, a np208, np241, and some np205's are 27 spline.

What you mean is 32 spline. That would have only been a 32 spline in 77-79 3/4 or 1 tons behind a TH400. Behind a TH350, its a 27 spline input.

The problem is that no one makes an adapter to go from a 4L65e to a NP203 that I know of. Its kind of the worst of all things. Since you will need to get new driveshafts anyways(4L65e is WAY longer than a TH350), you might as well just look for a later 80's 208 or a NP 205 with the 27 spline input. A late 80's 208 should bolt right up to your 4L65

 

[Vbb199]

What you mean is 32 spline. That would have only been a 32 spline in 77-79 3/4 or 1 tons behind a TH400. Behind a TH350, its a 27 spline input.

The problem is that no one makes an adapter to go from a 4L65e to a NP203 that I know of. Its kind of the worst of all things. Since you will need to get new driveshafts anyways(4L65e is WAY longer than a TH350), you might as well just look for a later 80's 208 or a NP 205 with the 27 spline input. A late 80's 208 should bolt right up to your 4L65

I always **** up that spline count because when I talk about say, a 4L60e vs a 4L80e on spline count, I'll confuse it with the possible 10 bolt spline counts haha.

Someone's gotta keep me in check.


Also, challenge accepted. Someone send me a 4L65e and a 203. I'll make an adapter for ya

 

[Bextreme04]

You will also need a controller for the 4L65. That will require, at a minimum, TPS and VSS inputs. Is this a 1987 TBI truck? How did it end up with a TH350 and NP203 in it?

 

[Bextreme04]

I always **** up that spline count because when I talk about say, a 4L60e vs a 4L80e on spline count, I'll confuse it with the possible 10 bolt spline counts haha.

Someone's gotta keep me in check.


Also, challenge accepted. Someone send me a 4L65e and a 203. I'll make an adapter for ya

What makes it even worse is that you COULD get a 203 with 31 spline input... but only in rare 70's FORD trucks

 

[rwljpl]

Thanks for all the info
If I found a 700r4, is that an easier connection to the np203?

 

[rwljpl]

Would I have all the same issues with a 4L70e, 4L75e, and 4L85e?

 

[Bextreme04]

700R4 would have been the original trans for an 87 TBI motor. No, it would not be an easier connection. I have seen some talk about being able to adapt the later model adapter to the 203 by drilling and tapping new holes. Honestly the 203 is just a POS anyways. I would be looking at replacing that before the trans for sure.

What year is your truck? What engine are you running? Any electronic transmission will require a controller of some kind that will want to know what the engine is doing and the speed of the vehicle.

 

[rwljpl]

My truck is a true Frankenstein—
— 85 cab
— Relatively new crate 350 ho
— TH350 three speed from 1977 but which is now shot
— NP203 transfer case from 1977, rebuilt at some point

I would like to avoid an electronic transmission if possible though I know the 4L60e can work with the 350ho because GM “connect and cruise” sells it that way

Transfer case leaks a bit but still works fine
The transmission absolutely must be rebuilt or replaced and I’d like to have a 4th gear

With those parameters, what’s my best option?

 

[Vbb199]

The only way you'll get past using an ECM with a 4L60e is to use toggle switches for the shift solenoids, and lockup solenoid and a 12 volt signal.

There's not alot of means to get around that.

Edit, or some sort of full manual valve body.