After attempting to help a hapless delivery driver with a totally waller'd transmission rear main seal that was leaking at a completely unsustainable pace it occurred to me that threr might just be one more way to get the bleeding beast back to civilization. Although I didn't have the relationship with the man to propose such an audacious idea my thought was this: Given that the rear main is in a non-pressurized portion of the case exposed to the same "airspace" as the pan could a desperate person just trying to make their way to civilization share the advantage of the natural anti-leak (of fluid) benefit of crankcase vacuum that we harness in the engine crankcase to the gasoline engine (pcv) to greatly reduce the pace of a seal leak in the automatic transmission. The idea is to remove the line that runs to the airbox and provides the engine with clean replacement air to the transmission dipstick and fill tube. I realize that the transmission has a small vent which will somewhat reduce the efficacy and might need to be capped off somehow if the situation is desperate enough.I believe that this might work enough to get a person out of a pinch and intend to test it at the next opportunity which will hopefully not be any time soon.
-- WcW, Feb 02 2024

How much vacuum is there available? Enough to pull splashing tranny fluid into the crankcase? How big a leak? If there is just enough suck to slow the leak, is there an advantage over just refilling until you get to help?
-- minoradjustments, Feb 02 2024


In my limited familiarity with mostly US truck applications the most common leaks that are quick enough to strand you are low pressure leaks around the pan or at the large seal at the output shaft. The volume of air that the crankcase will pull through such a restriction is not enough to migrate much in the way of fluid up the 3' long tube and even if it were to end up there the impact on the engine oil would be minimal.

While trans fluid is noted as "pretty bad" when fed directly into the intake manifold, the effect as a crankcase additive are more benign especially if the oil is changed soon after the addition.
-- WcW, Feb 03 2024



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