Posted by Gordon on Monday, March 18, 2002 at 12:35PM :
In Reply to: Pump it posted by Lyle Van Wert on Sunday, March 17, 2002 at 9:46PM :
Us DUKW owners and ex-DUKW owners no all about this topic.
You are not venting the axle at all, quite the reverse. If you are running down a highway or cross country you put quite a lot of heat in the axles. When you dump them in cold water they chill rapidly (as does the air inside them) and it creates a vacuum, which draws water in past the seals to mix with the diff oil.
The DUKW solution to this was to run vent lines inside the hull from each axle - on another vehicle you'd just have to run them above fording depth. You only need 1/8" diameter tube or so to allow it to work.
If you are going for positive pressure a DUKW owner worked out that it only needed about 4 psig to keep the water out of the diffs, more than that and you can blow the seals.
All this old army stuff has single lip seals, so there's no real point in pressurising them unless you swap them out with newer double lip types, and sometimes that means machine work to get them in.
Standard practice on DUKW work is to let the vehicle stand for one hour after it comes out the water, then just pull the lowest diff bolt to allow the collected water to drain out - it's easy to see when the water stops and the oil starts. Regular oil changes, etc, help.
As an aside, the redoubtable Mike Stallwood of RR Services (UK vehicle dealers) ran one of his DUKWs for ten years or more and never drained or changed the diff oil - he said he never lost a diff so why bother.
Gordon
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