This method easily removed all rust from the exterior of an axle housing as shown in the photos with 6-7 gallons of Evapo-Rust. If there had been rust on the interior (there was none), it would have been removed also.

An easier way to remove just interior rust only would be to cap the ends of the housing with 2 x 6 scrap drilled with the bolt circle of the outboard flanges to bolt on the wood scrap with a gasket. Then fill the housing with under 5 gallons of Evapo-Rust after degreasing.