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Does anyone have the size of the vent hole in the /5 4-speed?
I'm eliminating the speedo drive and my vent bolt has been replaced with a homeade job and I want to get the diameter correct on my replacement.
Thanks - Rod

Looks like about 1mm; it doesn't have to be much, it just needs to be there...

I often wonder why the vent and ground is in this horrible location.
The screw that holds the airbox mount on the top of the gear box seems like a much better place for the vent. The hole there goes right into the case and the bolt is 8mm instead of a wimpy 6. My battery is grounded to one of the starter mount screws as well as the frame.

A hole directly into the case would pump oil. I think the location makes sense in that it is as far from that oil filled interior section as possible... I wonder if, without it, the oil residue would make its way into the speedo cable as well as past the seal?

Bamboo812 wrote:A hole directly into the case would pump oil. I think the location makes sense in that it is as far from that oil filled interior section as possible... I wonder if, without it, the oil residue would make its way into the speedo cable as well as past the seal?

Point taken, but the final drive is set up that way, no oil pumping out of the vent at the top.
There shouldn't really be any oil pressure in the case, just air expansion caused by heat.
Air pressure would force oil past the seals at the lower level of the tranny, like the shifter, output, and input shafts.

The final drive is spinning at only around 750 rpm at 60 mph, the transmission shafts at that speed are turning over 4000 rpm, Big Difference!

Not to mention the speedo drive is vertical and has various venting / oiling features unique to it. The problem seems to be when the boot or vent leak water into the drive passage. The only corrosion in my trans was rust related in the speedo drive passage

Bamboo812 wrote:The final drive is spinning at only around 750 rpm at 60 mph, the transmission shafts at that speed are turning over 4000 rpm, Big Difference!

You may be right. I'm tempted to try it though.