It really sounds like there is something slipping when reverse pressure is put onto the drive line. Can you make it slip in reverse?

 

It's hard to say what exactly could be causing the problem until you figure out what is failing. On the one case I've seen that had gear oil run in it, everything was destroyed.. So it's no wonder your original case ate itself. Now the 2nd case, what fluid did you run in it? Did you make sure it's still full and the fluid looks good? How much can you rotate the front driveshaft with the hubs unlocked and the t-case in 4x4?

I've seen this problem before and it actually ended up being the t-case input shaft splines were stripped in an odd way that allowed the t-case input to slip on the trans output in reverse or under load when slowing down IIRC. The splines would just grab well enough to not slip under power in forward gears, but in reverse it would slip and grind. I remember being shocked that it would even go forward and grab.. That was on a Dodge t-case though.

The only guesses I could hazard without seeing the truck would be input splines, planetary gears, or the splines on the main shaft where it goes into the planetary gear. You'll have to tear it down to see what is really wrong.

I wish I had more pics of when I tore my t-case apart, but here is an album that has some of my t-case pics in it, just so you can see part of what your dealing with. Pretty much everything is held in with those PITA c-clips. The t-case pics in this album is a BW1356 just like in the 250s and 350s. Same t-case. Unfortunately I didn't take any pics of the input shaft or planetary gear, but the planetary gear is under the shift fork that you see in the pics and the main shaft that has the pump and chain gear on it splines down into the planetary.

Ford Truck Enthusiasts Forums - strokin'_tatsch's Album: F150 project...

 

Assuming your right, the next question is, can it be rebuilt? Or should I just start looking for a new TC now? And I had ATF in it, still full just slightly dark now. I would have drained it and looked for metal shavings just didn't have the time.

 

Yes it can be rebuilt. Judging by the DIY injectors in your sig, your capable of correctly building a 7.3L injector. If your capable of that, your capable of building that transfer case yourself. We've done quite a few of them now over the past couple years since first tearing one apart.. They are surprisingly easy to tear down and put back together.

 

Well my sticks are rosewood, however I'm not afraid of doing the work, just wondering about part avalibilty

 

Ahh, Jim built them for you. I assumed you did them using one of the kits that used to be available back in the day. Anyways. It is easy and the parts are available for you. You shouldn't have any problem getting any part inside the t-case.

I would tear it down and find the problem. Price the part(s) and if it's going to be too expensive, find a good used unit. I'm not sure how much the planetary or main shaft would cost.

 

I'll have to see if I can get my brother to tear it apart while I'm gone and do some parts shopping

 

What are the propshaft u joint angles with the lift in place?

 

Not extreme at all.. Even the truck I just got with a 6" lift doesn't appear to need a indexing ring