ATF leak thru shifter at high rpms

While racing at the dragstrip, I was getting an ATF leak from somewhere. The fluid level is/was filled perfectly level with the fill hole. I initially thought the ATF was foaming up and venting out of the vent tube on my T45.

But that wasn't it. I took the cover/boot off the shifter and watch it carefully. As the rpms climb up past 5000 or so, the ATF fills up the well around the shaft of the shifter, and starts overflowing out (see arrow in photo). Its not foaming or anything -it just looks like regular atf, overflowing. Also, no ATF seemed to be coming out of the vent hole.

I pulled the shifter, and checked for the plastic cup-looking thing. Its there, and looks normal. Any ideas?
Shifter = MGW, tranny = Promotion built T45, fluid = regular, nonsynthetic dex/merc

Will a clogged vent tube cause the fluid to overflow like that?

If its clogged and I unclog it, does it just means that the tranny fluid will pour out of the vent tube rather that the shifter?

TonyG said:

Will a clogged vent tube cause the fluid to overflow like that?

Click to expand...

Yes, I'm quoting myself...I thought about it and imagined how thats possible. ATF expands when it gets hot. The air occupying the space needs somewhere to go, hence the vent. If the vent is clogged, pressure builds and pushes the fluid out the shifter.

OK I'm game. Now I guess I'll try to blow thru the vent tube, if its physically possible.

So I removed the breather/vent tube from my T45. This is what it looks like:



It's a simple rubber tube opened on one end (the end that goes into the tranny), and closed on the other end.

The round bulb thing actually opens up like an umbrella like this:



Now along the wall of the tube there's a little triangular slit. This is where it vents the air. In the photo, I bent the tube a little so you can see the slit better:



I tried blowing into the tube (with the umbrella closed, like in the 1st photo), and I had to blow pretty hard to get air to vent. This is a little concerning to me, especially with 500+ rwhp. I get the impression that maybe an the stock breather won't cut it any more.

Also, this vent tube act like a check valve -it doesn't let air in. I would expect that when the shifter chamber in the back of the tranny get filled with fluid (during hard acceleration), it would need to some type of ventilation in order to drain back into the tranny.

I'm tempted to ditch this vent tube and go with a tube/hose that runs uphill to some type of breather tank.

Any thoughts?