4WD popping out of gear

[jd21476]

I was towing my jet ski this weekend and it was runnign fine until we got off hte highway. Then all of a sudden I lost all gears. Turns out my transfer case had popped into neutral. I put back in 2WD High and started down the road but as soon as I let off the gas it popped into neutral again. I put back in 2H only to have it do it again.

I wound up driving to the lake while holding the 4WD shift lever in one had to make sure it did not pop out.

Spent the day on the lake and drve home and it never popped out of gear again. My truck is a '73, 350, 700R4 automatic.
Any ideas?