oil pump question

[key]

A friend of mine who is many years my senior, is coaching me on getting my commercial license. He posed the following question to me for my weekends' homework to which I cannot find the answer..

What do you check when you replace a gear driven oil pump?

[double bubble]

How about oil pressure differential .

[key]

IT IS TO SIMPLE! but you probably have the answer.

KISS

[snipe70e]

Clearance