M5OD breather tube/fitting/location


Shran

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So this was a real treat... I got my rebuilt M5OD installed, put a couple hundred miles on it to break it in, and went to change the fluid while it was still warm. Apparently at operating temp it is pressurized, imagine my surprise when I got blasted with a 6' jet of ATF when I pulled the drain plug.

I cannot imagine that this is good for the seals nor can I think of a reason why it should be like this, no wonder the rubber shift rail plugs start leaking!!!

I'd like to add a breather somewhere. This is somewhat difficult to do now that the trans is installed. I would prefer to drill and tap the top cover and add a barb fitting but doing that is next to impossible with the trans in the truck and I don't really want to pull it again.

What does everyone think about drilling and tapping a hole in the fill plug and installing a 90* barb fitting with a few feet of hose going up into the engine bay and maybe a little one way valve at the top?

39468
 


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Ramcharger90

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Im surprised it was under pressure honestly. My M5ODR2 has never done that or my M5ODR1 for that matter. And I really didn't let it cool down, right up on the lift and drained it. My only concern would be the breather working as a supersoaker. If the line cracks at all
 

RonD

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How did you fill it the first time?

Could you have over filled it although I don't see how that would matter

I too have never run into that, and I also warm up trans before draining

I would maybe not install a vent yet
Refill and drive it then remove FILL plug FIRST to see if there is any pressure inside, if so something is wrong with the rebuild, something is getting TOO HOT inside


The shift rail plugs leak because the rubber dries out and cracks, it was never a pressure leak, just splashed ATF slowing leaking out
 

Shran

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I just filled it with a hand pump through the fill port like I've always done... I've done this many times with no issue but I've never changed the fluid while it was hot.

I did a bunch of searching and reading before posting this, it seems the group consensus is that M5ODs breathe through the shifter. That is totally accurate if the little boot on the shifter stub isn't ripped. There is quite literally no other way for them to vent - so if you've got all new seals and have installed freeze plugs, there is NOT a way for them to breathe at all. Every other transmission has some sort of breather tube on it... it just seems that this one should too, OR, it's supposed to be like this.

FWIW the fluid wasn't really hot. Lukewarm maybe at most and that was right after a 50 mile drive on the interstate on a 60 degree day.
 


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