New Guy Questions

[Agney5]

I'm a new Guy here, first post. I've browsed on here for awhile getting information but I'm down to my last couple questions i couldn't get answered just browsing.

I bought an 78 C10 that has K20 suspension and drive train. So my questions are related to Transfer case. I've got a 350 with TH350 with NP203 TC with part time kit. 10 Bolt front end with lockers and 14 Bolt Rear. So first one is pretty straight forward question, my shifter is labeled High, High Lock, Neutral, Low, Low Lock. So I'm driving in high which is 2 wheel drive to go to 4 wheel do i simply go to high Lock or do I then have to lock hubs and put in high Lock?

Second is I'd like to ditch the 203 for a 205 and the TH350 for a 700R4 I've yet to find else all would be involved in that process as far as parts and what not.

Thanks for the help guys and gals.

 

[Charlie]

 

[Agney5]

Thanks Charlie.

I guess I better post a picture of the truck.


http://i1244.photobucket.com/albums/gg562/Agney5/IMG_20180720_185336336_HDR.jpg

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[Craig 85]

Welcome. With the 203 lock in the hubs and pull it into High lock for 4WD. You can do this at just about any speed. You want to do this occasionally anyways as the chain in the 203 needs to be oiled. Once the part time kit is installed the chain only rotates when its locked. FYI you also have a 2 Low (Low position) with the part time kit installed if the hubs are unlocked.

 

[73c20jim]

Welcome from Tombstone, AZ

 

[Agney5]

So I do need to manually Lock the hubs to get 4 wheel then. That was my primary concern if they needed to be locked or just putting it in high Lock would do what I needed.

Yeah I know I need to be doing that on occasion with the 203 and I haven't simply from not knowing what I needed to be set at to get everything going right.

Thanks for the help.

 

[Craig 85]

If you are in Park or Neutral, you can pull the transfer case into High Lock or move it into the Low side. You will only be spinning the driveshaft and the front axle shafts if you do not lock in the front hubs to engage the wheels.

If you lock the hubs first, while in motion you're able to pull it in and out of 4WD at any time. Great for throwing rooster tails of mud at your friend's truck, then put in back into 4WD to get away.

If it's ever hard to get out of the Lock position, put it in reverse and drive backwards a little to release the bind.

 

[shiftpro]

Welcome Agney,
In order to run a 205 behind a 700r4, you will need to find an 205 with the 27 spline input shaft for starters. These came in 1/2 ton 4x4 automatic trucks with the T350 transmission.

 

[Agney5]

Ok I have a lead on a 205 now I believe it came off of a th350 but I'm going to have the guy check. For the time being that should be a pretty easy Tannertr over i think. Anything I'll need to consider?

 

[75gmck25]

The stock 203 is full time 4WD and has no 2WD position, so unlocking the hubs would be pointless. A stock vehicle with 203 would have fixed hubs. In its original form, the NP-203 is a very strong combination, but you are stuck with full time 4WD

If you have a 203 with locking hubs, its been converted to part-time, and the part-time kit uses some fairly weak parts. However, the cheap conversion was common because most folks felt it helped with gas mileage.

The NP-205 with adapter for TH350 was not a common combination in the 70's, so if you found one I would quickly grab it. Most 205's are set up for a 4 speed or TH400 and the adapter spline count is different. Its usually hard to find the right adapter for NP205 to TH350 (or 700R4). If you have access to the donor vehicle, I would also look at driveshafts and u-joint fittings to make sure you have everything you need to make the conversion.

Bruce

 

[Craig 85]

Milemarker used to make a complete output shaft on the NP-203, but from what I can find it was discontinued around 2010. I used this back in the early 90's on my K5. The ones marketed now are the second photo.

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[75gmck25]

I don't know when they discontinued the NP-203 shaft conversion kit, but I haven't found one in a catalog in several years. The shaft kit is supposed to hold up a lot better than the kit with just the four cogs and some spacers (your 2nd picture).

Bruce

 

[Agney5]

Ok sorry been away for a while. Yeah I'm aware of the weakness of the 203 with part time thus why I want to go to a 205.

So I've done some digging trying to figure out how to make it all work. So if I get a 700R4 which should be 27 spline and a 205 is as well. But the output shaft is a couple inches longer than the th350. So I'll need the adapter shaft from off road design I think. So let's say that all goes together as it should now will cross member need to be moved? Is there other parts that need to be replaced/modified? Presumably I'll need custom driveshafts? Currently they are slip yoke style. Is the torque converter going to be the same? Are linkage hookups going to kick my butt or is everything cross compatible enough to make this pretty easy? And lastly if i wanted to order a already built trans is there a place where I can explain what I've got for a setup and order the trans fitting those needs? Or do I say screw it and just get a 205 and leave the th350 for now? I'm mainly doing it for gas milage and a less maintenance needy transfer case.

Thanks again guys for the help.

 

[75gmck25]

I would have to do some research, but I believe the NP205/TH350 was used in GM light trucks in the late 60's and early 70's. Then in about '74 they started using the NP205 only with manual transmission, or with automatics in the 1 ton trucks. All the 1/2 and 3/4 trucks with TH350 started using the NP203. This means the adapter for the TH350/NP205, which I believe has the same spline count as the one used for the TH700R4, is relatively hard to find.

Bruce