NP203 question

My '77 came with a part time kit in the NP203. I bought a used NP203 to replace it, that was NOT converted, still full time. I had it rebuilt with a new chain. Is it OK to use this case with the lockout hubs that my truck came with, just leave them locked all the time and drive in "HI"? I just read a post somewhere else that using lockout hubs in the locked position with a stock full time 203 will destroy it. I don't know if I believe that, seems to me it's the same thing as the factory drive slugs. I am somewhat concerned with damaging the lockout hubs though, having them engaged all the time under load on pavement. Will I be OK? Truck has the stock 350, 6" lift, 4.56 gears, and 35x12.50 boggers. The only off-roading the truck will ever see is wet grass, maybe a little mud.

203 are fickle. I've had some that you can drive with manual hubs unlocked & then some must be locked. My 76 K10 was one that could drive unlocked. My son toasted the TH350 & we swapped the trans & case from a 75 & it will not move without the hubs locked now. It's also a noisy case so we're swapping ro the original case soon.

HS

Strick said:

203 are fickle. I've had some that you can drive with manual hubs unlocked & then some must be locked. My 76 K10 was one that could drive unlocked. My son toasted the TH350 & we swapped the trans & case from a 75 & it will not move without the hubs locked now. It's also a noisy case so we're swapping ro the original case soon.

HS

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The one that would move the truck with the hubs unlocked had to have been converted to part time then. That is the only reason it would have had manual hubs, otherwise it'd have just had the drive slugs instead of hubs. 203 trucks did not come with manual locking hubs. If it was still a full time case, the interal differential in the 203 would have sent all the power to the front drive shaft with the hubs unlocked. Path of least resistance. The one you swapped in from the '75 must have been a stock full time. The only way a full time 203 would move the truck with manual hubs unlocked is if it's in the hi loc or lo loc positions.

I'm interested in knowing if it's safe to drive the truck in "hi" with the manual hubs locked now that I have a full time 203 again, or if I need to see about putting the original front full time hubs back on.

Locked hubs do the very same thing as drive slugs.

Locked hubs should not be an issue for the NP203. If you leave the hubs locked tfor quite a while it might be a PIA or unlock them if there is dust and dirt in the mechanism, but it sounds like you don’t need to unlock them.

Thanks guys. I kinda figured that guy was wrong when he said manual hubs in the locked position would destroy the 203. So my Warn hubs will stand up OK to being in the locked position on hard pavement for normal street use? I was mainly concerned with that. Also, I'm getting conflicting answers on if it is A, possible, and B, advisable, to run the full time 203 with the front hubs unlocked. Can anybody with experience here clarify? I'd prefer to be able to unlock the hubs if I ever take a long highway trip, but some sources say that it will be bad for the chain. I always assumed that the truck wouldn't move at all if the hubs were unlocked, but according to ChatGPT,it will, and it's fine to do it, but I'd rather hear real-world input from people with actual experience. NOT asking about doing this with a part time kit. My 203 has been restored to full-time operation, and completely rebuilt.

You can run with the hubs unlocked, but you have to run the t-case in one of the "Loc" positions.

Lots of trucks were swapped to manual hubs, but no part time kit installed in the t-case. It was a cheap and easy way of taking strain off the front driveline. It all still spun, but the strain was gone.

These trucks always sucked for gas mileage, and folks tried all sorts of fixes to make it better.

I’d have to think a little more about running in hi Loc with hubs unlocked, and what it would do. It would be like running an NP205 in 4H and unlocking the front hubs. You would still be driving all the parts of the front axle, but just not powering the tires. I don’t think it would help much with gas mileage.

Don't run locked hubs with an unmodified 203 on hard dry pavement.

You can get away with that for a while as long as you drive easy and do large radius turns, BUT, the first time you do a full lock turn and press hard on the go pedal you are going to be breaking things. Which thing breaks will be based on which is the weak link. It'll probably be a u-joint. Maybe one in the drive shaft, which is no big deal to solve, but you might destroy something in the tcase, which of course is a much bigger deal to solve.

The best answer is a part time kit; the second best is running hubs unlocked; the explicitly bad idea is to run a 203 in Hi/Lo Loc with slugs or locked hubs. The owners manual and warning stickers will tell you the same thing.

Real world experience. Yes, I've broken things, repaired them, lived a better life afterwards.

There seems to still be a lot of confusion here, as misinformation is still being posted.

It's really not complicated...

*Non-converted 203 with factory slugs:
-Use as the factory intended.

*Non-converted 203 with locking hubs:
-Hubs locked, use as factory intended.
-Hubs unlocked, you must run in Low Loc or Hi Loc... even on hard surfaces!.

*Part Time Converted 203, with locking hubs:
-Use like any other 4x4. Low and Hi are 2wd, Low Loc and Hi Loc are 4x4. You can run with hubs locked or unlocked. Only shift to a "Loc" position on loose terrain, if the hubs are locked.

bucket said:

Locked hubs do the very same thing as drive slugs.

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I had the same issue with my 75 K10. Put manually locking hubs on and the truck wouldn't move unless the hubs were locked. I had an NP208 installed soon after and I can run in 2wd now. I didn't see much of an mpg increase but 1 or 2 mpg is better than nothing.

neiltee said:

I had the same issue with my 75 K10. Put manually locking hubs on and the truck wouldn't move unless the hubs were locked. I had an NP208 installed soon after and I can run in 2wd now. I didn't see much of an mpg increase but 1 or 2 mpg is better than nothing.

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Yes... on a non-converted 203, if you run selectable (locking) hubs, you MUST run with the hubs locked, OR the t-case in a "Loc" position. So that wasn't an "issue", but rather, just a fact of how an open differential works. Now, if your truck wouldn't move with the case in a "Loc" position either, then yeah, that was an issue. Possibly a shifter issue.