TH400 to 4L80E

[Peter J. Bierman]

On my to do list for next year is swapping the TH400 for a 4L80E.
A good one crossed my path but is comming out of a two wheel drive diesel truck.
I am not ( yet ) willing to drop the 4X4 set up so the question is;
Does anybody know if the 4X2 tranny some how will fit the NP208 transfercase.
With or with out adaptor or change of the outgoing shaft?

All input is welcome couse I have to decide if I buy the thing.

Peter

[grape]

your lucky....input from the 400 to the 208 is already the 30 spline as aposed to the 27 spline 700r4. I think even the adaptor in your case should be the same.

[dieselcrawler]

Correct me if I'm wrong, but it's my under standing that the 4L80E is the OD version of the TH400, right? I've heard said that the TH400 is very strong, how does the 4L80E compare strenth wise? And the 700R4? Is it compareable to the TH350? Just wondering, in my case, I'd like to have OD, but don't want to lose any strenth. I (ab)use my truck alot, mostly off road. Shifting from D to R and back with out stoping all the way takes it toll sooner or later!

Peter, hope all goes well if you decide to swap things out... let me know what issues you run into, that info may help me later this coming summer...

Greg

[Bobbie Martin]

Peter,
Keep in mind the 4L80E uses a computer to shift, so you will need the transmission computer and related wiring harness. In addition to all of the transmission sensors, you will need a throttle position sensor - it mounts on the DB2 injection pump and an engine speed sensor that mounts at the back of the engine on the cam drive. It will take a bit to get it all working but it should be worth it.

[Peter J. Bierman]

The one offered is from a 6.2 diesel ambulance.
It is a complete unit with all computers and stuff with it.
The big question is can a rearwheeldrive unit be modified to fit the NP 208 transfercase and if so what does it take?

Peter

[88 K30]

Originally posted by Peter J. Bierman:
The one offered is from a 6.2 diesel ambulance.
It is a complete unit with all computers and stuff with it.
The big question is can a rearwheeldrive unit be modified to fit the NP 208 transfercase and if so what does it take?

Peter My guess, from other tranny swaps, is that the output shaft/rear housing will need to be replaced. The problem is, I don't think the 4L80E was ever offered with a NP208, so you may be hard pressed to find the correct adapter. You might check with some of the larger 4wd shops online to see if anyone offers the appropriate adapter.

Good luck!

[john8662]

I think whats being asked is will a 2 wheel drive transmission mount to a transfer case (married t-case, not divorced). I was wondering the same thing. I know when it comes to 700R4 (JUNK Transmissions) there are two versions, one with a 4x4 case and one for 2wd trucks. I was wondering if there were differences in the TH400 and the 4L80E.

Is there a 4x4 case version of the TH400 that is different from the 2wd case? Or do you just have to swap out the output shaft (or tailshaft)?

Is there a 4x4 case version of the 4L80E that is different from the 2wd case? Or do you just have to swap out the output shaft (or tailshaft)?

I think thats whats being asked, I am curious as well. Thanks!

[Peter J. Bierman]

Thanks, that exactly what I mean.

Peter

[Dieselboy]

The 4L80E came with an NVG241 99% of the time. That's not too bad though.

Your NP208 has a six bolt hub and a 27? spline input, and so does a Chevy (88-91 non-ifs) NP241. Compatibility isn't much of an issue, but the real problem is the adapter and output shaft on the tranny side.

The cases are the same, but the adapters and output shaft are different...I think. ;)

I'm not sure, but you will probably have to change the shaft and adapter.

There are lots of guys that know more than me on the coloradok5.com forums. You might also look at Advanced Adapters.

[john8662]

So, if the cases are the same, you would have to come up with the new output shaft for the tranny and a new tailshaft-adaptor. To change out the output shaft you pretty much have to rebuild the transmission (since your there). I am now going on a search to replace my second 700R4 in my 4x4 project suburban for a better TH400 trans mated to the NP208. I don't think that the 700 is a good transmission considering the low torque the diesel puts out. My 700's always go to slipping from 2nd to third shifts and burn up in about a week. Have to check out ColoradoK5 as well for the conversion.

[88 K30]

That's essentially what I was trying to say. I guess I did not word my reply very well...

Nevertheless, the cases should be the same, just the output shaft and output housing should be different. In fact, I believe in most instances, the tailshaft housing just gets removed altogether. The transfer and adapter then bolt right up in it's place (with the proper output shaft length, of course).

There were plenty of factory TH400/NP208 units made by GM, but I think you will need a custom fabricated adapter for the 4L80E/NP208 setup. As was pointed out, Advance Adapters probably offers one, but the K5 board can probably give better details.

[Peter J. Bierman]

I did take a closer look at it and find the following, The outputshaft is the same size ( 32splains ) but longer then the TH400.
The boldpattern is the same so I either have to replace the tailshaft or fabricate a special adapter to handle the extra length.
Meaning the tranfercase have to go backwards like 3 or 4 inches.
The driveshafts and all the linkage have to be modified anyway so I think its doable.
In worse case scenario I go to 2 wheel drive....
To be short, I bought the thing and see what happens when I get to the swap.

Happy new year everybody !

Peter

[dieselcrawler]

WHAT? Go to 2wd? What are you thinking??? LOL, just givin' ya a hard time, if you've seen my truck, you'd know that it would NEVER be an option for me.
I would think that even with a K-5, you should still have a few inches to spare, and should be able to fit the adaptor that you would need. New drive shafts would be in order anyway, as you said, and I've found that on the front, a few inches longer will never hurt anything. Mine is maxed out with only a 6" lift, I've thought about a devorced transfer case behind a 2wd trans (700R4 if I found a goood one) for a little extra front drive shaft lenth, and a shorter rear. But my LWB truck won't miss any lenth in the rear, yours would be a bit tighter.
Hope it works out for you... Happy New Year!

Greg

[Peter J. Bierman]

Had a look under my truck today and there is enough space to slide the transfercase to the back.
So I think it's gonna work.
The adapter is more like a spacer to make the tailshaft fit, its easier then swapping the tailshaft off the tranny.
If it was a full length pickup going with the intermediate shaft would be another option, but with the blazer it put the transfercase on the trailer hitch ;) .

Oh and Greg,
As far the the two wheel drive option conserns,
you clearly have never been to Holland, its flatter then your driveway, and I have used the 4X4 3 times in 4 years and have been looking real hard for a place where it would make sense to go 4wheeling :D .
So it's more a wanna have not a need to have.
Beside it would save a lot off weight to lose the transfer and the frond axle internals.

Any way, I'll try to save the 4X4 first, to keep you happy..... ;)

Happy newyear

Peter

[britannic]

You'll need 4x4 for standing starts when you fit the new injectors/marine IP and add an NOS system and supercharger to complement your twin turbos :D !

[Peter J. Bierman]

I think I'll stop at 400HP and do believe the rear tires can handle that :D

Peter

[C.K. Piquup]

Hey 88K30,What transfer-case is in your`88?Is it still a 205?

[dieselhumvee]

just for the record http://www.transmissioncenter.net/4L80E.htm
offers a 4l80 conversion that does NOT require a computer to shift. the downside is that all upshifts and downshifts must be made by the driver, via the shifter, kind of like a race transmission.

[ 01-26-2004, 04:49 PM: Message edited by: dieselhumvee ]

[Dieselboy]

Originally posted by dieselhumvee:
http://www.transmissioncenter.net/4L80E.htm From the guys that brought you...The Raptor! :eek:

[Stage1]

On the 4L80E, is the transmisson computer located on the side of the transmission or somewhere elso on the vehicle. I am thinking about doing this swap also for my M1008 truck.

thanks,
Les

[britannic]

It's a PCM style box somewhere in the vehicle to keep it dry and snug.