4x4 won't work under load

[Q HAM]

Chevy 3/4 ton 81 on a 77 chassis full time 4x4

Had the truck about two weeks and I've buried it twice. 4x4 works fine climbing and n basic mud. Once I got comfortable I decided to put it to the test... Long story short... To the frame I went. In 4 lo I can't get my front tires or drive shaft spin. When I switch from 4 lo to 4 hi the driveshaft engaged but still nothing. Got it pulled out onto dry ground and it works just fine. This is my first 4x4 and I'm not sure what is going on. Any help would be awesome.

[sjracer]

what transfer case?

[92 s dime]

since he says FULL TIME and 77 im going to say a NP203
does the tcase make noise when its slipping?

[nvrenuf]

What makes you think 4wd is working on dry ground?

[joshgammill]

I had the same problem and it was the splines on the slip of the driveshaft going away. With out much load it would hold but once loaded the splines would spine inside themselves. The bottom part of the shaft wouldn't spin but the tcase side of the shaft would.

[Grumpy_old_fart]

203 chain stretch is also not out of reach.. its the most frequent culprit. I have only seen 2 bad driveshafts, and probably over 30 bad chains in 203's...

[Valley Rock]

One of the biggest mis-conceptions about the NP203 is that it is weak, and prone to failure. The main reasons the NP203 fails are use of improper lubricant and chain wear due to full-time four-wheel-drive operation.

The NP203 is actually a very bullet-proof case, and when converted to part-time and lubricated correctly, will last almost forever. Ninety percent of chain stretch and wear is caused by the fact that the chain moves (under load) continuously. The problem with converting one to part-time, is that not all parts get lubricated correctly. The design of the NP203 is such that it relies on the spinning of the chain to splash oil around the case to lubricate all the components. When the case is converted to part-time, the chain no longer spins (unless you have the hubs locked, or the case in 4wd mode). The item that needs oil the most is the rear tail-cone. It has an oil catch which the chain throws oil into. This oil is pushed by a plastic oil pump gear into the rear output shaft bearing. This oil catch needs to be refilled occasionaly, and the only way to do this is to drive in 4wd (or lock the hubs). MileMarker recommends running the truck for aproximately 10 miles every 200 miles. This is most easily accomplished by simply driving to work one day a week with the hubs locked.

[Loftis61]

Is your front driveshaft actually spinning?

I'm calling busted front axle with open diff...

[Q HAM]

Sorry guys for the delayed response. Light bill had to be paid b4 the internet! I took my trade cover off and found a couple of the teeth chipped off the big gear. My drive shaft does spin when I'm on dry ground and it will spin when I punch the throttle. Not sure where to go from here. Also I'm guessing ur assumptions are accurate on the type of tcase being a 203 since I have no idea how to tell the diff my self. Thanks for all ur responses. Ima nooB

[Q HAM]

Ummm so... I said I removed my t case cover but it was my front diff that I meat had the chipped tooth. Sorry. Like I mentioned b4 I'm new at all this

[Q HAM]

There is no noise when it slips. I just drained the t case and removed all bolts for the cover. I'm hoping I can get to this chain. Today

[Q HAM]

I took the cover off my t case. Through further research I did find it is intact a 203. Chain looked reasonably tight the top was slightly looser than the bottom. All the gears appear to b in good shape. I did come across some info that made me question the hubs. Maybe they are slipping????

[Beat95YJ]

Please stop using text shorthand. It is annoying as hell.

[JunkCJ6]

Sounds like it is not going into loc. There should be 5 shifter positions, 4H Loc, 4H, N, 4L, 4L Loc. If it doesn't lock then you will only spin one end when you get it suck good