I would really like a turbo 400 in my truck

Jimmyperf400 said:

I built my 700r4 with every after market performance part they make and I've towed a 10 thousand pound excavator with the 1990 gmc jimmy its in and I've never had any issues. But up to you you know what you want.

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alot of people refuse to hear stuff like this from a 700R4.
It would not not cost alot to have one built correctly. You also dont need expensive parts.
They just have a bad name cause people dont know how to adjust the TV cable.

Jakewalter, Talk to Nicks Transmissions here on the forum. He can do anything you want.

Late to the party...

If swapping out a 700/208, a 400/208 combo is a direct replacement. Shafts will still fit. If you don't want to replace the transfer case, you'll need a 32 spline input for your current 208.

While I don't tend to be a fan of the 700r4, a properly built one is perfectly capable of hauling around a 4k load on a regular basis.

What gear ratio is in the axles?

jakewalter said:

I have a 85 K20 that I built up to haul our 3500 pound pickup camper.

It currently has a pretty healthy big block that I built for torque.

The transmission is a 700R4 and a 208 transfer case.

While on vacation a couple of weeks ago the transmission started slipping and I lost reverse.

I never use the overdrive and as for mileage I threw my pencil away a long time ago.

Other than a TH400 out of a 4wd what else would I need?

I would really appreciate any input that you guys could share with me.

I need to apologize.

The guy that rebuilt my transfer case said that it is a 208 not a 203.

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There’s a dude in the next thread down with a turbo 400 looking for a 700r4 setup. You two should spend the weekend together.

The first gear ratio of a 700r4 is a steep 3.06, the TH400 and 350 are right at is 2.52, depending on where you get your info. 4L80e are relative cheap to buy, and upgrade. Friend with a 700r4 in a 650 horse gen 1 427 cost him over 4000. I have ridden in that car and did not like the big jump to second gear, 4.11 rear gears.
As mentioned above, 400, and 4l80e have 32 spline output, and as stated previously are fairly easy to install. However my 205 needed the large bearing in the TC, so it needed machining. You may need your driveshaft modified. The 4l80e needs a controller My favorite: https://www.usshift.com/usq4rd.shtml. I say this so that you can be aware of some options I have tried/driven/had personal experience with. Bucket says that they are a direct . Study!!! I have a 700r4 that I could put behind my 6.2l Detroit diesel for cheap, however long term reliability for me is hands down the 4l80e. Mine has 45000 miles late model with all the upgrades 450 bucks. I will modify my drive line and tc myself, (journeyman machinist). bought the tail shaft adapter from Trans Dap couple hundred. All told less then 2000, but should last a lifetime. I will use the same trans behind the modified LQ4, or Modded 454, havn't decided which motor.

Good morning everyone,

I would like to thank all of you for your advice and input.

I have decided to rebuild my NP208 and replace the input shaft to a 32 spline.

Now I need to find a good place to order the rebuild kit and the input shaft.

Any thoughts would be appreciated.

I don’t mind paying the extra cost for quality parts.

Thanks so much,
Jake

jakewalter said:

Good morning everyone,

I would like to thank all of you for your advice and input.

I have decided to rebuild my NP208 and replace the input shaft to a 32 spline.

Now I need to find a good place to order the rebuild kit and the input shaft.

Any thoughts would be appreciated.

I don’t mind paying the extra cost for quality parts.

Thanks so much,
Jake

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These guys are experts and have anything you might need. They carry the good stuff and have excellent customer service. I have rebuilt 2 t-cases and an NV4500 using them.

I bought my 32 spline output shaft for my 205 from Advanced Adapters. Comes with the bearing, (bigger OD in my application,) yours may have the bigger OD already, but check. They are great to deal with as well, been around for a long time, and great tech line and customer service.

I have a adapter for sale ..

My 2 cents is to build the TH400 bulletproof and add a gear vendor.
Or you can get a 700R4 that's built to handle the torque as well. - a cheaper option.

I did this swap last year on my 83 k2500 suburban, its definitely worth it even though youre losing overdrive. I had the T400 built to handle 800hp with super strong everything including billet shaft and drum etc. It was 3800 total installed and worth every penny on how it shifts, the only thing is finding the right parts. If you can get them sourced all together id get it from nasty-lsx and be done with it. It took 2 weeks for my shop to find the right stuff

I have a TH400 with a 208 as well, and I like it a lot. Very reliable so far, seems able to handle the work.

jakewalter said:

I have a 85 K20 that I built up to haul our 3500 pound pickup camper.

It currently has a pretty healthy big block that I built for torque.

The transmission is a 700R4 and a 208 transfer case.

While on vacation a couple of weeks ago the transmission started slipping and I lost reverse.

I never use the overdrive and as for mileage I threw my pencil away a long time ago.

Other than a TH400 out of a 4wd what else would I need?

I would really appreciate any input that you guys could share with me.

I need to apologize.

The guy that rebuilt my transfer case said that it is a 208 not a 203.

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What gears are in the truck? If the mxo trans, ie 700r4, was OE then it came with 3.23, 3.42 or 3.73 gears.
The higher 2, no OD wouldn’t be bad, 3.73s would be marginal.
Guessing if you aren’t using OD with a big ole 454 that you have tall gears.

75BEASTK20 said:

My 2 cents is to build the TH400 bulletproof and add a gear vendor.
Or you can get a 700R4 that's built to handle the torque as well. - a cheaper option.

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Gear Vendor is ridiculously expensive and nowhere near worth the $. Add almost $4k on top of buying a good TH400 and you could do about anything else you wanted for the same $ or less and have better end product.
GVs have gone the way of the dinosaur.
A built 700r4 would be the easiest swap for sure. I know folks say they’re fine for moderate power if built right, but ifn I was removing the trans and looking for years of trouble free service and a lot of miles and loaded like the OP, I would use the 700r4 as a bouy anchor.

Grit dog said:

Gear Vendor is ridiculously expensive and nowhere near worth the $. Add almost $4k on top of buying a good TH400 and you could do about anything else you wanted for the same $ or less and have better end product.
GVs have gone the way of the dinosaur.

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I'd still buy a GV... you know, if I could afford it, lol.