I have a 1977 sc f250 with 460/c6 and divorced t case np 205. I can shift it into 4 hi but just rear wheels spin. Driving down the road I can hear kind of rumbling from the t case. In my drive way I tried 4 lo and it would just grind, and it ground getting it back in 2 h. I shut the truck off and it shifted fine into all positions, put it in 4 lo and started up no grinding but the truck would kind of lurch and you could hear it kind of banging or thumping. I am assuming that I need to replace, but until I do how will it affect everything while driving in 2 hi.
Kind of long sorry, I've had the truck about a month and a half , and there has been more things wrong with it then I thought. Any information would be great.

 

when you are shifting into 4wd is the trans in neutral and the vehicle at a complete stop?
You should be able to just pull back on the lever to enegae 4 hi. 4 low requires a slight technique, and each case has its own personality. You do not want the lever to stop in neutral, because with the engine running it will grind. Shutting the engine off is the best bet to minimize the grind.
Now, if you "lock" the front hubs, you shoud have 4 wheel drive in both low range and hi range. Locking the hubs and engaging the transfer case on the pavement will bind tha case, and the truck will hop during any type of turn. This can get pretty voilent and can cause some damage if you do this too much.
You can unlock the fornt hubs and engage the transfer case to determine if the noise is actually in the case. Heak you can really pull the front driveshaft off and unlock the hubs so the front end cant turn at all. This will isolate the problem to either the case or the front end. If the noise goes away, then you can start looking at the front axle for buster parts.
It is doubtfull that you have broken a 205 transfer case, but it is possible. I would be looking at other things that might be broken, like the front spider gears or an axle shaft.

 

Thanks for your response 75. It all started a couple days ago when we had a huge snow storm, locked the hubs shifted to 4 hi and nothing, just spinning all over, and noticed the banging and thunking. Oh and I forgot to mention that before the snow I was underneath checking fluid levels in the the front and rear end and t case. Everything looked good except the t case it was dirty and had shavings in it.
After I read what you posted I went out and drove with out locked hubs and put in 4 hi, the noises started you could hear it and kind of feel it right behind the drivers seat, when I shifted back to two hi it went away , I do have two u joints that need replaced one on the rear driveline and the other from the tranny to t case.

 

You could remove the PTO cover from the side of the case and take a look inside of the thing to see if there is anything real bad.
Sometimes the bearings can fall apart. I have seen this before. You can also remove the bearing retainers to see if the bearings are wasted. Just make sure they go back together the same way they came apart. The retainer has a hole to oil the bearing and it has to go on the correct way or the bearing will starve.
This is just a start. These cases are strong, but the bearings can fail once in a while.

 

Ok I got under it and pulled off the front and rear drive lines. I started it up and put into gear no noise from the t case then put in 4 hi still sounded good so it got me worried about the front axle like you mentioned. I pulled the cover off the pumpkin and everthing looked good, I turned the front driveline by hand and I could see the knuckles turn by each wheel. Then I locked in the hubs same thing it was really easy to turn the driveline , not like trying to move the front wheels at all.
So any Ideas? I'm thinking hubs are bad, but I've never replaced them before. Also I'm still learning things but when the truck is in 2 hi is the front drive line still supposed to spin?

 

The front driveline should not turn when the case is in 2wd. You can turn it by hand to verify that it is competely disengaged.
The only way that the front driveshaft could turn at this point is if the front hubs were locked.
Alright so you started some troubleshooting. You have made some decent progress, and I applaud you for removing the inspection covers. This is exactly what they are there for, and this is the intended use. Good job there. You would be suprised how many folks dont want to hassle with these 10 little bolts.
Alright from your description, everything is leading to either a broken or stuck hub assembly, or a busted short shaft.
Still very easy to determine. Once you turn the yoke (pinion) and you look for the axles to turn within the knuckles, (provided that you have both hubs locked) you should not be able to turn the yoke. If you can, then look to see which axle is turning. Should only have one turning if the hub is bad, that axle will turn since it is not engaged. So if you look closely at the knuckle, and you see one shaft turning, then you can start to narrow down your search, and remove the locking assembly and inspect for damage. It could be that the thing is broken, or just not fully engaging. Only a visual inspection will tell.
Maybe this wil help you. You can copy it, and print so you can have a reference where you are working.