Transfer case oil pumps 101
There are two types of oil pumps, a ball check valve type and a shuttle check valve type. I have no information to know when each type was made but I have only ever seen the ball type shown in the TM's. I have 3 pumps, 2 are the shuttle type.
I hand primed mine until my hand went numb and could never get it to prime, it was the shuttle type. I used a suction pump from a brake bleeder kit to pull oil from the transfer through the output of the pump, even then hand action showed little results. I don't understand how hand priming is better or necessary rather than letting the transfer pump it, someone will have to explain it to me. The best way I found was to inject some lucas oil right into the outlet pipe of the pump, re connect the clear tube, put transfer in neutral, select 4th gear and let it pump. Observing the flow of oil in the clear tube it's obvious that it takes a lot of pumping action to get that oil flowing, it actually pulses not a steady flow.
A discussion with another member provided a lot of this information on the pump types and what seemed to work best. Given his own experience and what I discovered it appears the ball type of pump works the best. It is sound advice to make sure you have clean oil in the transfer and be sure to add up to 50% Lucas oil stabilizer to ensure pump reliability.
