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Keep NP203 or ???

J

JohnNoble

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I posted this in my build thread but haven't received any responses so reposting here.

I currently have a 203 transfer case with a part-time kit in it. I've just purchased a 14 ff and will be purchasing a D60 for the front. What is your advice regarding the 203 case? Keep it and run it? Find a 205 instead? Also, I just read a thread from 2003 about running 10w-40 instead of gear oil in the 203 t-case; I'd never heard of that until today. Is that really good advice?
With the swap to D60 front and 14 ff rear will both drivelines need to be modified for length? Or should both still fit assuming I keep the same lift; currently has 4" lift and I'm thinking I may go to 5" during this process.
Thanks!
 
Driveshafts should be fine.

The 203 is personal preference really. The 208/241 both have better low range ratios. Is this a blazer with a TH350? A 205 will bolt in place of the 203 if so, if it has a TH400 you need a different trans output shaft.

The 203 should use 10w30 motor oil not gear oil. The 203 never spec'd gear oil.
 
If ya do keep the 203 definitely change the gear oil out for the thinner stuff ( GM manuals call for straight 30 weight ) because 90W can’t properly lube all those 4 billion small needle roller bearings in that case and will cause serious wear over enough time.

As a side note - I’m more of a 205 fan and the 208/241’s deeper low range is nice if needed but if all is well with the existing 203 and ya don’t feel like making the effort to convert let it ride.
A 205 will give ya the longest rear driveshaft length and that may help with a lifted short wheel base of a K/5 if needed.
 
I have run 203's for a lot of miles. They work fine, I don't have any now. I did keep the range boxes off 2 for building doublers. ORD has rebuild parts for the range box side of the 203. I dont think there are many parts available for the chain drive and center differential part anymore. It may be wise to work towards a t-case swap before you find yourself needing to swap one in a hurry if the 203 fails.

The distance from axle centerline to the yoke is definitely not the same from 1/2 ton to 1 ton axles. Its not a huge difference but there is one. Your driveshafts will probably still work but make sure you are not near the bottom of the slip, it will break stuff. I snapped a 208 in half bottoming out a driveshaft once upon a time. You will need a bastard u-joint to hook up the new axles.
 
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Anymore if doubler just go magnum from ORD gets 3 speed case . . Doubler is 2 speed only .

If i could find a super nice np203 for a th400 i would like it for my plow truck as lots of plow guys rave about the full time 4x4 back in the day .
 
sweetk30 said:
Anymore if doubler just go magnum from ORD gets 3 speed case . . Doubler is 2 speed only .

If i could find a super nice np203 for a th400 i would like it for my plow truck as lots of plow guys rave about the full time 4x4 back in the day .
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If you already have a 203 range box that bolts to your trans the regular 203/205 will work great and save at least $1000. 3 speed is nice but the ratios really aren't that different, its not like the purpose built 3 speed cases.
 
I have 2 doubler 203/205 . I wish i had the 2.72:1 middle gear a magnum offers . There is times i would love a in-between 2:1 and 4:1 .

I had the parts and got deals . . But if i had to do another 3 speed . Thats my feedback on them .
 
BJs offroad has the 2" chain for 203s. The only trouble I had was finding the needle bearings to return the 203 from part time back to full time. They are available but you need to hunt for them from bearing manufacturers not parts suppliers. Ebay also has a good amount of parts available for the 203s.
Keep in mind I'm not using mine for rock crawling or extreme off-roading, just cruising.
 
sweetk30 said:
Anymore if doubler just go magnum from ORD gets 3 speed case . . Doubler is 2 speed only .

If i could find a super nice np203 for a th400 i would like it for my plow truck as lots of plow guys rave about the full time 4x4 back in the day .
Click to expand...
Twenty years ago when I was talking with Casey at Wagner Machine Shop about converting my 203 range box from 2:1 to 3.2:1 one of the selling points was the feedback from a wrecker/tow truck/plow truck business up in Oregon that had this upgrade done and they raved about having the extra gearing being perfect and the benefits of a full-time case in the snow and icey roads.
I figured that if the gear set was holding up to that kind of usage it would do just fine - plus it gives a nice gear ratio splits of 1:1, 1.96:1, 3.2:1 or just shy of 6.3:1 with all big ole helical cut gears used.
That being said I still think that a Magnum setup is awesome!
 
73K5BlazerSS said:
BJs offroad has the 2" chain for 203s. The only trouble I had was finding the needle bearings to return the 203 from part time back to full time. They are available but you need to hunt for them from bearing manufacturers not parts suppliers. Ebay also has a good amount of parts available for the 203s.
Keep in mind I'm not using mine for rock crawling or extreme off-roading, just cruising.
Click to expand...
Please correct me if I am wrong but didn’t the K20’s & K30’s and 4-spd equipped K5/10 203’s come with wider 2-1/2” width chains and sprockets ?
I am assuming that the aftermarket only offers the more common 2” stuff these days?
 
tarussell said:
Please correct me if I am wrong but didn’t the K20’s & K30’s and 4-spd equipped K5/10 203’s come with wider 2-1/2” width chains and sprockets ?
I am assuming that the aftermarket only offers the more common 2” stuff these days?
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I could be wrong but I believe the 2.5" chain came a few years later. Maybe late 70s ? Once the 2.5" chain was out I think all 203s had them. IIRC the 2.5 chain had a steeper pitch and was capable of handling slightly more torque. Now I gotta look this up.

Edit: I had it backwards, the original chain was the 2.5".
 
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73K5BlazerSS said:
I could be wrong but I believe the 2.5" chain came a few years later. Maybe late 70s ? Once the 2.5" chain was out I think all 203s had them. IIRC the 2.5 chain had a steeper pitch and was capable of handling slightly more torque. Now I gotta look this up.
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I had never considered that it might’ve been a late model running change for all 203’s.
I recall our main parts house supplier telling us what I said up above when we had a 2.5” instead of a 2” but they could’ve been wrong - can’t recall what years of any of the wide chain 203’s that came through the shop but I do recall several being K20’s and one 79 K30.


Please let us know what ya find out on this?
 
sweetk30 said:
Anymore if doubler just go magnum from ORD gets 3 speed case . . Doubler is 2 speed only .

If i could find a super nice np203 for a th400 i would like it for my plow truck as lots of plow guys rave about the full time 4x4 back in the day .
Click to expand...
I have a 203 for a 400
 
No one is reproducing 2.5” chains so you have to convert to 2” if you need a chain, they you have to find sprockets…..it’s all out there but it is getting harder to find.
 
I'm not sure how accurate the info I gathered is but here it goes. Supposedly in 1978 the original 2.5" 3/8" pitch chain was swapped for a 2" 1/2" pitch chain. It was less likely to skip teeth when the chain stretched. It also provided a horsepower rating increase around 19% at 1200rpm and 22% at 3000 rpm.

Interestingly the military humvee t-case uses a similar 1.25" wide chain with a 1/2" pitch. So I guess it would be plausible to say that the NP203 chain is stronger due to the additional width.

BJs offroad
https://bjsoffroad.com/np-203-transfer-case-chain-only-made-in-usa-hv-005/
Has a reproduction 2" or 2.5" chain for sale. This chain has the 3/8" pitch on both widths and will not work with the 1/2" pitch sprockets. I got one about 2 years ago when I rebuilt my 203. It still needs drive shafts among many other things, so I can't speak on its performance.

I researched the 203 before I decided to rebuild it and feel that it's an extremely stout full time unit. Many installed the part time kit not realizing that when in 2wd it doesn't properly lubricate it's components causing damage. I believe the kit suggested shifting into 4wd every so often to sling oil around the case. Also many people assumed it was best to run gear oil instead of straight 30. The chain may not last as long if it's exposed to alot of shock load, although that would be the same for any chain driven case.

Mile marker makes a 509 chain saver kit which allows you to take up any chain slack as it stretches. This eliminates skipping teeth on the sprockets and claims a 3x longer chain life. That would probably make it a lifetime chain if used properly. If anyone has this 509 kit lying around I'll buy it.
 
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Humvee is also planitary hubs at wheels so a lot less load on driveline . And the dana center diffs are 28 or 30 size mid 2:xx ratio . . . Oh and 6.2/6.5 raw power :pimp:
 
sweetk30 said:
Humvee is also planitary hubs at wheels so a lot less load on driveline . And the dana center diffs are 28 or 30 size mid 2:xx ratio . . . Oh and 6.2/6.5 raw power :pimp:
Click to expand...
H1’s actually use AMC 8-7/8” inverted diffs ( instead of Dana ) to work with the two-gear portals and no planetary at the hubs.
 
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