Swapping 203 to 205 on turbo 400

[Rubble]

I'm going to convert my full time 79 3/4T to part time. Can I use the same adapter that the 203 is mounted to? I'm planning on putting in a 205. TIA.

[b454rat]

Nope. Tranny output shaft is too short. Need to swap to a longer one, which depends what version 205 you have....get a part time kit for the 203....

[Rubble]

That sucks,I've got an extra 205 & would've been easy then.

[RedRoad]

why not go doubler?

[Rubble]

Originally Posted by RedRoad

why not go doubler?

Most of the time I only need 2wd for this truck, otherwise 4 high & low is good enough. Been digging around on pirate & looks like I can bolt the 205 to my turbo 400, just need an adapter.

[b454rat]

You need to research more. The tranny output of a 203 is little over an inch. The 205s have 2 different lengths. This is from offroaddesign.com, just says how to use a 203 behind a 400 tranny.

1: Use a factory configuration. The TH400 was available with the NP203 in heavier duty trucks (3/4 and 1-ton generally) in approximately '78-'79. The factory configuration uses a 1 3/8" stickout 32 spline shaft in the TH400, a 32 spline input gear in the NP203 and a 1.1" adapter plate between the two, somewhat similar to the TH350 adapter plate. This is the shortest way to mate the TH400 and NP203.

2: Use a TH400 that originally had an NP208 mated to it. This TH400 uses a 32 spline shaft that sticks out of the case about 2.5" and has an adapter housing that's about 2.5" thick. You'll use a TH400 version 32 spline input gear in the NP203 and re-drill and tap the face of the NP203 with the round bolt pattern to match up to the NP208 adapter housing. Benefits of this kit are the parts are quite common since the NP208 was very widely used with TH400 trannies. The drawback is the adapter is about 1.5" longer than the shorter factory configuration.

3: Use a TH400 that originally had a NP205 behind it. This TH400 uses a 32 spline shaft that sticks out about 4.5". You'll need to use a factory TH400 to round pattern NP205 adapter housing that is 4" thick and once again, re-drill the front face of the NP203 to match the round pattern. The input gear will be the TH400 version NP203 32 spline input. Drawbacks to this system are the overall length with the 4" housing between the two and the expense of buying the factory housing. They're not common as used parts and typically must be purchased new. ORD can supply this adapter.

[jjzepplin]

What was your np205 out of? There are many configurations of the Np205.

[Rubble]

I've got a turbo 400/208 combo out of a 82 I parted out a few years ago,might just go with that set up. I've had good luck with 208s in the past & way easier to R&R than that 205 anyway.

[jjzepplin]

I guess if you don't 4 wheel much it should be fine. Is something wrong with the 203?

[Rubble]

My 205 was behind a turbo 400, nothing wrong with the 203.

[SilverMiner]

Originally Posted by Rubble

My 205 was behind a turbo 400, nothing wrong with the 203.

Just this spring I completed swapping in a TH400 that had previously been mated to a 203 and converted it to 205. Knowing what I know now, I wouldn't repeat it. There was nothing wrong with the 203, but I lucked into a 205 set up for a 400 and thought it was the smart route to go. I had the output shaft converted at the same time the trans was rebuilt, bought the adapter from Off Road Design, and then had to pay more money having driveshafts converted to the new lengths.

There are a million NP205 fan boys on the internet, and the poor old NP203 has been catching flak in magazines since the mid 1970's, but when I managed a fleet of high-mileage 70's squarebodies in the 80's doing mineral exploration work the 203 rarely was a source of trouble (one bad chain out of 18 trucks, burbs and blazers). I got a lot of practice adjusting the shift linkages, but other than that the trucks rusted to death long before the transfer case died.

[kwmech]

The bad rap that the 203s got was the fact that they ran in 4wd all the time and suffered from the chain stretching and subsequently the chain jumping the teeth on the gears and eventually breaking, thus blowing the bottom of the chain case apart. The gear box itself is just about dynamite proof unless you run it out of oil. The other issue was the shifter box with adjustment. Most of the time the box just got full of grime and would not work properly. Twin sticks are available. With a twin stick and the full time delete kit, I do not see any reason why it would not last and take abuse when needed.