1974 F250 4x4 Auto NP203 manual hubs

A couple months ago I posted on here how I thought my transmission was toast because it was slipping. The original problem was if the front hubs are 'locked' and the transfer case is in the 'unlocked' position, any acceleration at all will cause the truck to feel like it slips into neutral. When I let off the gas it grabs again but after I begin accelerating it breaks loose again.

I tested driving with the transfer case 'locked' and my manual hubs 'unlocked' and the truck drives and shifts great. So I assume that rules out the trans. So I then thought it must be the transfer case? I topped off the fluid (about 1.5 quarts) and took it out but was still having the same issue.

Then it dawned on me that a more likely problem would be a bad hub that when it breaks loose all the power went to that wheel causing the feeling of being in neutral.

I went to a steep dirt-hill climb to test and had the front hubs 'locked' and the transfer case in 'low' 'locked'. The truck crawled right up about 3/4 of the way when a clunk/pop type noise happened towards, the front of the truck, and then lost all traction in the front with the rear wheel now spinning as well.

So I am thinking its a broken hub, I'm pretty green to all this and don't fully understand how it all works. So what is the best way to go about testing for a bad hub? Sorry for the long background story...

Thanks for any help or suggestions!

 

Best way to test for a bad hub is to remove it and look at it.

If is a very simple way to get to learning about your truck. My truck had been run in 4x4 on city streets, to "keep everything running right" by the PO. Well, he busted one, lol.

I knew nothing about it, but i took it off and yep, obviously busted. I started combing the junkyards removing hubs, seeing how they were put back together, and taking pictures. I finally found one that was complete and would fit my truck, got it for $6 and installed it.

Anytime that i am going to do work on my vehicle, i go to the junkyard and pull it apart there. It is ok if you break something or find out that you dont have a tool for the next step.

 

^^ thanks for the tip.

 

^^^^^
These are the tools you need, around $10-$15

Remove the 6 Allen screws, and set it aside on a clean rag.



^^^^^
You will then remove the snap ring. Make sure you use a snap ring tool, it can not be removed otherwise without damaging the ring.


^^^^
then, using your picks, you will remove another ring. Its kind of a bugger but will come out. You can see it at the bottom of the pic, and in the last pic next to the picks.


^^^^^^
After those 2 rings are removed, temporarily screw 2 screws in on opposite sides, and pull gently, your hub assembly will come out as a unit. After you get it out, remove the phillips screw that you see in the pic. Be ready, because the gear and large spring will pop out.


^^^^^^
These are all the parts. Clean the old grease off everything and check for damage. Regrease before you reinstall, and regrease if you replace.

Very simple job. Will take you awhile the first time, but will turn into a 10 minute job once it makes sense to you

 

Ok, you already know this, but...

The transmission engages or disengages the rear drive shaft to the rear axel through the rear differential. If you are in Park/Neutral, and rev the engine, the rear drive shaft does not turn, so the rear axel does not turn, so you go nowhere, right?

Ok, the transfer case does basically the same for the front axel. When you have the transfer case "unlocked", it is not engaged, so it does not turn the front drive shaft, and the driveshaft does not turn the front axels.

When you "lock" the transfer case, you are merely turning the driveshaft, which turns the front axels. So to that point, it acts the same as the transmission.

So, if you drive your truck in 4x4 (transfer case locked, hubs unlocked) you are sending power to the rear drive shaft and front drive shaft. Both driveshafts are turning, and both axels are turning (basically).

Ok, now lets say you lock your hubs. You are locking them to the front axel (spindle shaft) so now your wheels turn because the transfer case, driveshaft, axel shafts and wheels are locked together.
So far so good?
Ok, so now you locked your hubs, and unlock your transfer case. What is happening? Well, your wheels are locked to your axel shafts and driveshaft, but your transfer case isnt. So when your wheels turn from driving in 2wd, your axel shafts and front drive shaft turn with it, because the are all locked together.

So, when you are driving with the hubs locked, transfer case unlocked, you are only rotating the axel shafts and front driveshaft from the wheels, so your feeling of "Neutral" has nothing to do with the transmission or transfer case.

This is a very nontechnical explanation, hope i didnt confuse you more, lol.

 

Thanks for the pictures and steps posted above that's very helpful.

Now isn't the NP203 transfer case a full time 4WD transfer case? So with the transfer case unlocked, power can be sent to any of the 4 wheels and the power would go where there is least resistance, so if I have 1 wheel in the air I wont be going anywhere. With the transfer case locked I will have power both going to the front and rear wheels.

Thats why (assuming I have a bad hub), I can drive around with the transfer case locked and hubs unlocked with no problem, but with the transfer case unlocked and hubs locked whenever I accelerate the truck 'breaks loose/neutral' and I stop moving and can hear a free spinning sound (driveshaft and/or axel??). If I unlock the hubs and have the transfer case unlocked, when I put it into gear the front drive shaft just spins and the truck doesn't move.

 

I think that's right. I'm not sure what the benefit of the hubs is on a full time system, however. Unless its been converted to part time? Running in "lock" with the hubs open would still make all the front drivetrain spin. The transfer case would drive the front axle. I am thinking the OE setup did not use switchable hubs. Maybe easiest/cheapest to find a set of the simple drive hubs used as OE. Always "locked".