In order to confirm that all Deep Water Fording (DWF) vent lines, transmission seals, differential seals, etc are sealed, a leak down test is required.
Pictured above is a leakdown tester we assembled. We used a 1/4″ NPT brass tee, a 1/4″ NPT x 1/4″ hose barb, a 1/4″ NPT x Schrader valve, and a low pressure gauge (0-15 p.s.i.).
You may note that we used a glycerin-filled gauge. A glycerin-filled gauge adds a level of dampening in an application where shock-loading frequently occurs. It is unnecessary for this application, however the cost was only slightly higher than a non-filled gauge. Of note, filled gauges often have a small brass plug mounted in rubber to allow you to zero the gauge out if atmospheric pressure has raised it from zero.
WARNING AND CAUTION: We highly recommend using a hand pump, such as a bicycle tire pump. Should you put excessive pressure into the system while testing, it is highly likely that you will “blow out” seals, and potentially damage seals in the engine, transmission, gear hubs, and differentials. It takes a very little amount of air to reach 2 to 3 p.s.i., and even use of regulated air may provide a “burp” of air at a pressure sufficient to dislodge or destroy seals.