1969 Chevy 4x4 rearend?

I was hoping someone could answer a question for me? I own a 1969 chevy truck, 4 wheel drive, granny gear 4 speed tranny, small lift on it. When i engage the transfer case to 4 hi and lo and lock the hubs, the back right rear tire slips and the truck hops. I think its because the gears in the front and rear diffs are different, but i'm not sure. Can somebody help me out?  

Hi tchasstain06 I have never seen what differant gear ratios do to a 4X4 but it sounds like it would be funny to see but your right and it will break something. The only real way to tell is pull both diff covers and check the #s on them or count the teeth on the crown and the pinion and make sure they are the same.Divide the crown gear # of teeth by the pinion # of teeth and get your ratio. The 4x4s run a little differant ratio like 3.07 in front and 3.08 in rear they wont be identical.It's a pain in the rear but probable can't go by any tag # if there is a chance someone changed them.Go for a new set to match the higher # if you drive it on the hyw a lot you get better milage.  

Could be, in the past, someone broke an axle, and just installed whatever they had lying around.
I'm with autotec, on popping the covers.  A tube of silicone is a lot cheaper than a twisted driveline, or broken axle shaft.
The ring gear should have (among all the numbers) two numbers with a dash between.  That gives you your tooth count.  Sometimes its a pain to count pinion teeth.  
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1949 Chevy 1 1/2ton, home-built hydraulic wrecker.  Rustoleum industrial black, with flames.  Flamethrowers out 5" dual stacks.
1962 Chevy C-20, 402BB, 4-speed, 3.90 positrack. Hauls my camper.... among other things.
Kaiser M35A Deuce, 4x4 4 wheel steering *work in progress*