205?

[Desertstorm]

I've recently purchased a 1978 K20 and I am thinking about changing out the 203 full time transfer case to a 205. The truck is a 350 with a 350 transmission, what 205 will fit? what is a 205 figure 8? What spline count should I be looking for? Will a adaptor plate be needed? Thanks in advance.

 

[dvdswan]

Welcome to the site.

IMO, unless your 203 is trashed, just do a part-time kit to it. They are a very stout t/case, only issue is a stretched chain, and a rebuild is easy fix.

If you still want to swap to the 205, you will need a new driveline as the 203 is about 10" longer.

You need the figure 8 adapter piece.

You need to change the output shaft on the transmission.

If you find a donor at a junkyard take the drivelines, trans, t/case, adapter, and mount.

 

[RoryH19]

Welcome to the site.

IMO, unless your 203 is trashed, just do a part-time kit to it. They are a very stout t/case, only issue is a stretched chain, and a rebuild is easy fix.

If you still want to swap to the 205, you will need a new driveline as the 203 is about 10" longer.

You need the figure 8 adapter piece.

You need to change the output shaft on the transmission.

If you find a donor at a junkyard take the drivelines, trans, t/case, adapter, and mount.

Exactly.
This is my thought for my 78 k10. Unless I find a donor with all the parts the 203 is staying.

 

[bucket]

If it's actually a th350, it's not that difficult of a swap to a 205. The trans output is the same.

But if it's actually a th400 like in most K20's, the trans output has to change and you will need a big bearing 32 spline 205, which are spendy.

 

[TubeTruck]

A figure 8 pattern will have a bolt pattern that looks like this:

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A 6 bolt round will have one that looks like this:

You must be registered for see images attach

As @bucket said, most K20's came with a TH400. Verify your transmission and transfer case before you do anything. If you in fact do have a TH350/NP203 the swap will be easy as long as you get the 205 with the correct spline count (which I think is 27). If you have a TH400/NP203 you will need a NP205 with a 32 spine input. You can spend months looking for one and save lots of cash because they are expensive. Or you can buy any NP205 that has the correct bolt pattern and have the input bearing bore machined to the bigger bearing size. ORD makes and sells everything you will need to make this conversion. The input swap is about $250 plus machine time.

 

[bucket]

With the th400/203 combo though, the output shaft on the trans is much too short to use with anything else. So to use a 205, the correct trans output needs swapped in. Or change the trans too.

 

[shiftpro]

ORD has all these 205 parts if needed.

 

[Desertstorm]

After a little more research I now know for sure my 78 K20 has a TH350-203 transfer case setup. The front axel has warn manual locking hubs, the only way to get the truck to move is to lock in the hubs which is contradicting to what I've been told about it being converted to part time. If it was converted wouldn't it have manual hubs? If it was converted why would I have to lock in the hubs to get it to drive? Could it be possible the previous owner installed the warn hubs and didn't convert the transfer case? I'm thinking now that I might remove the 203 and install a new conversion kit, a new set of drive chains, and a twin stick set up. What a mess!

 

[Swearbody]

I live in the 205,lOl

 

[bucket]

After a little more research I now know for sure my 78 K20 has a TH350-203 transfer case setup. The front axel has warn manual locking hubs, the only way to get the truck to move is to lock in the hubs which is contradicting to what I've been told about it being converted to part time. If it was converted wouldn't it have manual hubs? If it was converted why would I have to lock in the hubs to get it to drive? Could it be possible the previous owner installed the warn hubs and didn't convert the transfer case? I'm thinking now that I might remove the 203 and install a new conversion kit, a new set of drive chains, and a twin stick set up. What a mess!

If the case has not been converted and the hubs are unlocked, the truck will only move in HI Loc and LOW Loc. It will not move in HI or LOW. If it's been converted, it will move in HI or LOW as those are actually now 2wd HI and 2wd LOW.

Lots of people put manual lockouts on the hubs, but didn't convert the case. It doesn't serve much purpose.

 

[bucket]

Also, if you can't count 5 distinct positions in your shifter, it probably needs cleaned/lubed/adjusted.