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M5OD Transmission Leaks Bad On Long Drives

Tshark299

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A strange problem I've never encountered: My M5OD 5-speed leaks like crazy after being on the highway for longer than 30 minutes or so. I can drive for weeks around down and it stays relatively dry, but after cruising at about 70mph for a while the whole underside is coated with fluid from the transmission back. The entire tailgate gets coated with ATF too.

A couple years ago the shift rail plugs started leaking so I RTV'd them back in place and it stayed dry for a about a year. Then it started leaking a little from the top again - this time seemingly from the seal around the shifter. So I dabbed some RTV around that which helped for a few months but it's leaking again... and steadily getting worse as time goes on. The leak started as a quarter-sized spot after a long drive but now the pavement is starting to look like a crime scene under there.

One time I pulled off the highway after a 2 hour drive and noticed the transmission seemed very hot. The dripping fluid was steaming off the transmission. I only noticed that once though. Not sure how hot manual transmissions normally get after cruising in 5th on the highway for a couple hours (i could have easily burned my hand on it that time) so not sure if that observation correlates or not.

Any ideas as to why my transmission seems to build pressure, get hot, and spray fluid out of the top any way it can during longer drives??
 



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arco777

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Maybe you have a bearing going bad and generating excessive heat, or a slipping clutch, or something like that? Manual transmissions shouldn't generate enough heat to cook like that...
 






Tshark299

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Maybe you have a bearing going bad and generating excessive heat, or a slipping clutch, or something like that? Manual transmissions shouldn't generate enough heat to cook like that...
Definitely not the clutch slipping - I just replaced it as soon as it started slipping last year.

I had the bearing thought as well but it's not making any noises which I'd think it would if a bearing was letting go. The old 5-speed in my Jeep started making a noticeable whining noise whenever the clutch was out because of a failing bearing but nothing like that with this one.

Even if it was getting hotter than it's supposed to though, would that cause it to constantly force fluid out of the top? I mean, I could see fluid coming out while it's heating up, but once it reaches its temperature (even if it's hotter than it should be) I wouldn't think fluid would keep being pushed out.
 






arco777

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Clogged vent tube? The auto has a vent tube but I'm not sure on the 5-speed. Maybe some freaky overpressure and then a siphon effect going on?
 






Tshark299

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Hmm interesting vent tube idea... can anyone confirm if the M5OD does or does not have a vent line? I should know since I've dropped it twice but my memory isn't great when it comes to these things...

If there is a vent... then there's no reason why it should be building so much pressure, right?
 






arco777

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The attached troubleshooting page mentions a vent, but I couldn't find one mentioned in the other diagrams and instructions.
 

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Tshark299

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The attached troubleshooting page mentions a vent, but I couldn't find one mentioned in the other diagrams and instructions.

Interesting that it mentions a vent because from what I can find the M5OD does not have a vent. I quickly looked under mine with a flashlight and didn't see anything. Then I found this thread: M5OD vent? which seems to confirm there in fact is not one. I also found this thread on The Ranger Station about adding a vent to the M5OD: Replacing the rubber plugs in a M50D-R1.

I might start with re-sealing the shifter, possibly with a new retainer and go from there unless anyone has a better suggestion!
 






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