I don't think that there would be any damage to the rear end, but the TOD WILL throw a fit if one of the tires is smaller, or has lower air pressure, than the others. VXSport is correct in that the odd sized tire needs to go on the front where it will give the TOD less of a headache. The smaller tire in the rear will trick the TOD into thinking that one of the tires is slipping so it will try to throw power to the front wheels, constantly, which will make the transfer case engage and disengage all the time.
Only problem now is that if your tires have some pretty significant wear on them buying a new tire could cause you the same problems as running the spare in that the new tire will be bigger than the other three.
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