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3-Synchro Gearbox Part - "The Pill, 22G89"

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dklawson

dklawson

Yoda
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Later this fall I will rebuild the gearbox in my Mini. There are a few parts shared between the early Mini and Spridget gearboxes. I'm looking for information, observations, and measurements for "The Pill", BMC part number 22G89.

This is a hardened pin, radiused on both ends. It is 3/16" in diameter but I don't know the exact length (it is approximately 9/16" long). It is used on the 1st/2nd selector hub on 3-synchro gearboxes. It is supposed to somehow control/prevent overthrowing the shift which in turn prevents the selector hub from spewing out its detent balls and springs.

My questions are:
1) Does anyone have one of these 22G89 pins that they can measure with calipers? My practice/parts gearbox is missing this and a couple of other parts. I can make a practice pin out of an alloy dowel but I need the end-to-end length measurement.
2) Can anyone explain how this pin is supposed to work? I can see that it goes into a full radius groove on the gearbox mainshaft and that sliding motion of the synchro hub SHOULD allow the pin to lock the inner part of the hub to the mainshaft. I just don't understand what's supposed to happen and still have the outer ring of the hub able to move to engage gears.

Any observations and measurements will be greatly appreciated.
 
Hi Doug,

Length is .560" and diameter is .186"

If you look carefully at the cogs on the inner side of the 1st gear ring, you'll find that only one has a ramp to one end of the ring. This ramp must be aligned with the position of the hole in the inner hub where the "pill" is inserted. Getting the inner and outer hubs oriented to each other in any other way will prevent you from selecting 2nd gear.
 
Thanks Gerard. I used a 3/16" alloy dowel pin and made a pin that length. I carefully installed the inner hub in the outer ring so the ramp would engage the pin.

After fitting the hub assembly to the mainshaft I am still unclear the purpose of the pin. I know it is necessary for shifting but I didn't see what it actually does. Can you shed any light on the function of the pin? How does engaging the ramp with the pin alter the action of the 1-2 hub?

Thanks for any general information you can offer.
 
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