The Trail Tech computer I'll use has its own reed switch
speed sensor, so I won't need the trans speedo cable. I also wanted to arrange a trans vent hose to both avoid the OE hollow trans bolt and to have the ability to put the hose into the air box to draw moisture out of the trans when water gets in there from a river crossing or whatever.
I made up this trans vent plug from aluminum. Also shown is the stock trans plug that attaches the speedo cable.
This is an updated trans vent drawing
. I haven't yet made one to verify the updates, but I think it should be OK.
I measured the trans hole as 19.0 mm. The design uses a 1/8 NPT hose barb fitting for the outlet, but to keep the plug's profile low I decided to turn the threads of the hose fitting down and just epoxy the fitting into the plug. I put a metric 16 x 2.0 o-ring on the bottom of the plug to keep oil from seeping up and out of the fastening bolt and the top of the plug.
O-rings seal by being squeezed between mating parts, the terms 'squeeze' or 'crush' are generally used here, and is expressed as a percentage of the o-ring cross-section. Generally, for a static cylinder plug like this a crush of around 20%+ is recommended.
The machined edges of the trans, both at the hole's opening and at the edge formed by the cross drilling of the fastening bolt were sharp and made it difficult to install the plug without cutting the o-ring at 20%, so I reduced the crush to about 17% by cutting the groove deeper. I also put a chamfer on the trans opening, but it was still a careful operation to install the greased plug.
Here's the assembled plug.
And the plug installed in the trans.