The original fluid spec for the BW1356 was synthetic MERCON automatic transmission fluid, however this has now been replaced by MERCON V (Ford no longer produces MERCON ATF and MERCON V meets the previous specifications). Do NOT use gear oil in the BW1356 - it has an internal fluid pump that keeps the bearings lubricated. The pump is NOT compatible with thick gear oils. Draining and replacing the fluid regularly will prolong the life of the transfer case and keep the 4 wheel drive engagement smooth, positive, and reliable.
Click any thumbnail image to view full-size
• The drain and fill plugs are both located on the back of the transfer case. The drain plug (lower of the two) is towards the driver side while the fill plug is located toward the passenger side (looking at the rear of the case). Both require a 3/8" square drive (socket wrench of small breaker bar) for removal/installation.
• Place an oil catch can below the drain plug.
• Remove the fill plug first! If you remove the drain plug first only to find out later that the fill plug is stuck and/or stripped, you've got a much bigger project on your hands. If the fill plug comes out without trouble, then remove the drain plug and drain the transfer case completely.
• Once the fluid has drained completely, reinstall the drain plug after cleaning it and applying a couple of wraps of oil resistant Teflon tape.
• Use a fluid pump to pump fluid into the transfer case through the fill hole until fluid begins to run out (the fill hole also acts as the fill line). Once the transfer case is full, replace the fill plug after cleaning it and applying a couple wraps of oil resistant Teflon tape.
• The actual fluid capacity of the BW1356 is spec'd at 2 quarts. Ford calls for MERCON synthetic ATF - do not use anything other than synthetic ATF in this transfer case.