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NP-203 30 weight motor oil AKA SAE 30 non-detergent motor oil.
NP-205 80/90 gear lube.
To help ID it there is a blue/silver tag on the front of the xfer case.
All Highboys had divorced transfer cases, as opposed to married transfer cases. A married transfer case is bolted directly to the transmission. A divorced transfer case is bolted onto its own cross-member, and is separated from the transmission by a driveshaft. Highboys had Dana 24 part-time transfer cases from 1967-1973, and either the standard NP205 part-time or optional NP203 full-time transfer cases from 1973-1977.5. The NP205 is the strongest and most desirable factory transfer case.
The Dana 24 is a cast-iron, gear-driven, part-time, 2-speed case with 1.86:1 gears. The NP203 is a chain-driven, full-time, 2-speed case with 2.00:1 gears. The NP205 is a cast-iron, gear-driven, part-time, 2-speed case with 1.96:1 gears.
10w30 or 40 is the correct oil. The 203 depends on the chain "splashing" fluid into the tail housing. The gear oil is too thick for this and tranny fluid is too thin too "stick". https://www.bobistheoilguy.com/forum...-transfer-case
Yes that is a divorced NP-203 "full time, transfer case". Uses 30W motor oil and is "sling" lubed. I would suggest to at least once a month take it down a dirt/gravel road and lock it in Hi Lock and get to slinging some lube around. I would even do a little idling along in Lo Lock for good measures. Do you have full time front hubs or lock in, lock outs? AKA the part time conversion.
People often diss the 203, but I happen to like them! When I finally stumble across a hiboy I hope it has one. I wouldn't even convert it to part time. I had good luck with them in some old dodge power wagons. Yes they suck fuel and they are heavy as hell. Probably need a good rebuild too. But they are strong (IIRC used in trucks up to 10,000 gvwr...just like the 205) and up to the task.
Unfortunately this truck hasn't seen the attention it needs over the past couple years. Hasnt been driven much at all. SHortly after I added my new front lift spring i noticed the t-case was leaking slightly and leaving a small puddle in driveway. I havent drove it much since. I need to figure out the leak, but will go ahead and top off fluid with some 10-30
embarrassed to say, but I have never even used the truck in 4wd since i have owned it, so will plan to do that more often. Hope i haven't caused any harm by not running in 4wd. anything special to do to engage and disengage 4wd? Truck does have manual locking hubs
Great info 77&79F250!!! I always liked not having to jump out and lock hubs. I rarely ever needed the Loc position. When in Hi or Low, the differential in the 203 would send the majority of the power to the rear, and maybe 10 or 20% to the front. When in the Loc positions, it's 50/50 front and rear just like a part time t case would when engaged in 4wd.
Thanks for all the help! Just Added 1 qt of 30w to the case. Hope that wasn’t low enough To hurt anything.
been reading up on the 203 case. I did see a few people say you can just lock the hubs and drove around for a little while and that would lube everything also. Any thoughts? Not sure what all has been converted/changed on mine, if anything.
I found that the case is leaking from the bottom bolt on the rear of the case. Here is a picture. I am guessing I need to remove all these bolts and reseal this plate?
There were a few different part time conversions for the 203, but all of them suggested driving around with the hubs locked in for a few miles every so often to splash lube everything in the case. I have heard of people extending the fill hole up with a 90° fitting to allow more oil in the case (basically over filling it) but I don't think that's the way to go. Resealing that cover should be an easy job. You can get a look at the internals while you have it open.
Yes make a gasket sealer will work. Make sure to get one that is oil resistant.
And if your truck moves with the hubs un-locked, you have a part time kit installed in the transfer case. If you have the shifter in two HI.
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