Automatic hub questions

[keegs1974]

So I have a 74 1500 with the automatic hubs in the front and I don’t get how they work I understand that one tire in the front always spins but that’s about it when I put it in hi lock or low lock what engages the diff to lock is there a vacuum line or something I’ve only ever had manuals and also does that back end lock too because if it that definitely doesn’t work

 

[Ellie Niner]

I'm guessing you've got the full time 4wd setup with NP203 transfer case. If so, and it hasn't been modified, you'll have flat-ish chrome caps on your front axle ends where you'd usually find the manual locking hubs of a standard part time setup. If so, you're in 4wd all the time, and there is no provision to unlock the front axle, as it's always in use. What allows you to drive on high traction surfaces in 4wd, is that there's a differential in the 203 T-case that keeps the front and rear axles from winding up on pavement and such. Most of the full time 4wd trucks I've encountered have open diffs in the front and rear (though you probably could've gotten at least a limited slip in the rear... and maybe the front too?). With the transfer case in High or Low, you'll have roughly the same power delivery to all four wheels, though if you've got one tire jacked up in the air, it should (at least theoretically) spin at 4x the speedometer reading. The High Loc and Low Loc positions lock out the center differential, making the vehicle perform exactly like a part time 4wd for use in extra low traction situations. It has no effect on front or rear axle diffs.

If you have a NP203 with manual hubs up front, someone has converted it to a part time setup, though the quality and depth of these installations was often done in a half ass manner. I've never owned a full-timer, but if I did, I wouldn't bother to try and convert it... even though I wouldn't mind having 2L for certain situations.

 

[75gmck25]

@Ellieniner provider an explanation, but I’ll expand it a little.

- front is an open differential, so one tire spins if you get stuck. You could add a front locker that actuates with a dash switch, but they are expensive. In normal driving on pavement you do not want it locked.

- the rear axles had a G80 Gov-Lock option, so check the sticker on the glove box door. The G80 is a simple locker that engages a locking pawl if the wheel RPM is about 200-300 rpm different between the two rear wheels. However, if you spin it up quickly (e.g., try to do a burnout) it might lock up too violently and break the locking pawl. That is why it’s called the Gov-Bomb. It is not a GM Positraction axle like you would find in a Chevelle.

If there is no switch on the front axles, it is engaged all the time. That setup is durable and requires minimal maintenance. It also means you probably have a stock NP203.

 

[Grit dog]

Unless it has a much newer front axle or hub setup, you don't have auto hubs, you have full time 4wd. My only comment on them, is we had 2 of them, 3/4 tons 76 and 77 models, back in the day at the landscape company I turned wrenches for in high school. They were used all year, unlike some of the trucks, working in the summer, plowing in the winter. I worked there from '88 to '92.
The reason I don't know much aboot them, is I never had to repair them....unlike many/most of the other trucks.
Hi and Lo Loc doesn't lock the axle diffs, it locks a differential in the transfer case.

 

[keegs1974]

Oh ok now eventually I wanna manual swap the truck I had brought a parts truck a while back and I wanna put the manual in mine the it’s a munchie 4 speed atleast I was told so haven’t really taken a good look but could I run the np203 with a 4 speed or will it only or on the auto

 

[AuroraGirl]

Oh ok now eventually I wanna manual swap the truck I had brought a parts truck a while back and I wanna put the manual in mine the it’s a munchie 4 speed atleast I was told so haven’t really taken a good look but could I run the np203 with a 4 speed or will it only or on the auto

you need a special rarer than dirt version of the nP203 and adapter (early 70s blazers/jimmy with 4 speed I think, 4x4) which the eaasier way is probably a sm465 and np205 combo. is it an auto parts truck? if its a 1973-1980 4 speed its probably np205 if its 81+ its probaly np208 (205 were still around tho, and clutches changes to hydraulic in later 80s)

NP203 was auto, 4x4, till 1979 basically.

 

[75gmck25]

Np203 was offered with all the transmissions, but most common with the TH350. However, the transfer case adapter spline count has to match, and GM used different output shafts in the manual box than they did in the automatics. It might be easier to find a mated set of trans and transfer case and use the entire unit.

 

[bucket]

you need a special rarer than dirt version of the nP203 and adapter (early 70s blazers/jimmy with 4 speed I think, 4x4) which the eaasier way is probably a sm465 and np205 combo. is it an auto parts truck? if its a 1973-1980 4 speed its probably np205 if its 81+ its probaly np208 (205 were still around tho, and clutches changes to hydraulic in later 80s)

NP203 was auto, 4x4, till 1979 basically.

I have one of those 465/203 adapters and the 10 spline input too. They used to be worth a bunch of money to people that wanted to run a 203/205 doubler with a 465. But nowadays there are better gearing options so I think the market value for the rare adapter plummeted, lol.

 

[AuroraGirl]

I have one of those 465/203 adapters and the 10 spline input too. They used to be worth a bunch of money to people that wanted to run a 203/205 doubler with a 465. But nowadays there are better gearing options so I think the market value for the rare adapter plummeted, lol.

Id run one without shame, its not like im ever going to be looking at MPG with c6p and all the extra welded on steel as it is. The weight reduction from nature also cant offset it LOL