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A whale of a transmission problem

Thursday, December 4, 2014 - 09:00
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“There she blows!” was a famous quote from the 1956 movie Moby Dick. Well, from time to time our technical helpline receives calls with shops fighting a whale of a problem. That is, a transmission blowing fluid out of the vent or worse yet, out of the fill tube if so equipped. OK, corny I know, but nonetheless, when you have an issue in the shop that holds up other work, it can become whale of a problem.

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There are not too many causes to consider when fighting with this type of problem. One possible reason can be related to pump cavitation. If a pump can suck in air past a filter seal or anywhere between the filter and pump, this unwanted additional air intake will surpass the vents capability to exhaust it. The fluid will become aerated, rise up and blow out the vent and/or fill tube.

Another cause is due to an over filled transmission. As obvious as this may be, you would be surprised as to the many times the wrong dip stick has found its way into the fill tube. Most often we have seen this occur with fleet accounts where the company owns vans or trucks of the same manufacturer but with different engine sizes and transmissions. For one reason or another, a dipstick from one truck inadvertently gets placed into a different vehicle. It comes to your shop to be fixed and when done rebuilding the transmission or whatever repair you’ve decided to do, you are now fighting the problem it originally came in for; fluid blowing out the vent. You decide to change the pump thinking it’s warped or defective (which is another possible cause for this problem). Yet the problem remains. The decision is made to change the entire transmission and guess what? Yup, it still blows fluid out the vent.

One way this should have been detected is by the amount of fluid put into the transmission. Let’s take a 2004 Ford F350 4WD Super Duty with a V10 using the Torqshift 6R140 Transmission. Fluid fill specification for this transmission when dry is 19.2 quarts (18.0L). If one or two extra quart was put into the transmission, you would think this would catch someone’s attention. By the way, 6R140 pumps are known to distort blowing fluid out the vent when hot. But never assume your dip stick is giving you the correct level. Check it before turning this into a whale of a problem when all along it was just small fish to fry.

Another cause for fluid coming out the vent or fill tube is due to the transmission fluid overheating. There are several possibilities for transmission overheat and will be the subject of a following newsletter.

One last possibility is quite rare. Depending on the configuration and location of the vent, leaking sealing rings, blown out gaskets or missing baffling can allow fluid pressure to spray towards the vent. Cross leaks are another rare possibility but when it is a problem, it will allow pressure to intrude into the vent circuit. 

And there she blows!

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