2HI, Locked Hubs, "Jumping" Front End

[NYBumkin]

I have been reading up on the NP208 and Spicer 60 Trac-Lok system for my M1028. I have read where some say it is ok to lock the hubs and run in 2HI when there is a possibility of needing the 4WD (not meant to be locked all the time). When I lock the hubs, stay in 2HI, the front end "jumps" when making turns. This led me to believe that my transfer case may have an issue? I am aware that in 4WD with the hubs locked the "jump" is expected...

Thoughts?

 

[Gunzy]

Sounds like your transfer case is actually in 4hi and not 2wd. Unlock your hubs and go under and see if you can turn the front driveshaft by hand. If not you are in 4wd.

 

[cpf240]

I'd check the u-joihts at the front hubs, perhaps one, or both, are frozen or binding

 

[Skinny]

I would guess in this order of probability...

-no one has put the correct LSD additive in the front end in quite some time, massive amounts of chatter while turning
-bad front ujoints
-tcase not shifting out of 4HI due to worn shift fork pads
-tcase is not properly shifting out of 4HI due to incorrect adjustment on the linkage or failing body/driveline mounts

 

[sandcobra164]

My M1028 almost does this. It pulls very hard to center when the front hubs are locked and your on a high traction surface. With the truck in neutral and the front end jacked up, both tires turn the same direction. Mine is one that the VIN starts out 1GHD which I've read often indicates a locker of sorts in the front differential. Could that be the issue the OP is having?

 

[Gunzy]

My M1028 almost does this. It pulls very hard to center when the front hubs are locked and your on a high traction surface. With the truck in neutral and the front end jacked up, both tires turn the same direction. Mine is one that the VIN starts out 1GHD which I've read often indicates a locker of sorts in the front differential. Could that be the issue the OP is having?

That would fall back to not having the proper friction modifier in the gear oil.

 

[Skinny]

Mine doesn't chatter because I make sure to put the additive in but its very common on poorly serviced clutchplate LSD's. I used to see lots of Jeeps come in and do the same thing at the dealership. I fluid service with some figure 8's used to do the trick. My M1031 does the same thing with the hubs locked in. The return to center on the steering wheel is much higher with the hubs in.

 

[sandcobra164]

As far as I know, the diff fluid in mine is from 1985 and probably had what the engineers considered the correct fluid as built. I have taken samples, they show no worries about swapping the oil out even though it´s almost 32 years old.

 

[Skinny]

Please tell me that is suppose to be a joke...

 

[NYBumkin]

Ok...so the first test I did was to unlock the hubs, shift into 2WD and try to spin the forward drive shaft by hand. Not moving, definitely feels like it is in gear. Speaking with a mechanic here at my job he said maybe a fork is broken. I can shift, at the transfer case by hand, 2wd to 4WD, and all seems tight in the linkage and external shift arm at the transfer case. I am trying to minimize down time when I drop the transfer case (which seems inevitable at this point) by understanding what is or could be wrong in there.

Thoughts?

 

[porkysplace]

Ok...so the first test I did was to unlock the hubs, shift into 2WD and try to spin the forward drive shaft by hand. Not moving, definitely feels like it is in gear. Speaking with a mechanic here at my job he said maybe a fork is broken. I can shift, at the transfer case by hand, 2wd to 4WD, and all seems tight in the linkage and external shift arm at the transfer case. I am trying to minimize down time when I drop the transfer case (which seems inevitable at this point) by understanding what is or could be wrong in there.


Thoughts?

Tm TM9-2320-289-34p.pdf
Gives a Illustration of a disassembled NP208
on page 192

 

[cpf240]

...Thoughts?

Baring finding the problem elsewhere ( u-joints, correct fluid, etc ), perhaps get a spare transfer case and rebuild it, then just do a swap in an afternoon.

 

[Gunzy]

Try to disconnect the linkage and use a wrench to attempt to shift it into 2wd. If you can it is a linkage adjustment problem. Also attempt to verify it will go into Low range and Neutral too.

 

[Chaski]

At least the NP208 is an easy transfer case to work on.


1) Buy some transmission assembly lube online before you take it apart (used to hold the dozens of roller bearings in place.
2) Take it apart on a bench with a lip, or on an old chunk of carpet to contain the dozens of rollers that will fall out.
3) An NP 208 for a TH350 or a 700R4 is identical to one for a TH400, except that it has a different input. The inputs can be swapped, so don't be afraid of a project transfer case that came off the wrong transmission. There are enough guys on the forum that have done a 700r4 swap that someone probably has a spare TH400 input if you need it.
4) Rebuild kits with new seals, rollers and plastic fork tips can be found on online auction sites, or places like Transparts warehouse in Redding CA. You will have to buy a chain separate if needed.