I have noticed after stripping a few gearboxes that some detents have two grooves, one on each side and some have non. Which are the best and when did they change.

I don't know, the condition of the ball end is more important, imo.
Last time I needed some they were NLA and I had to make a couple from silver steel and harden them.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

My guess is the grooves allow oil past in both directions so that if the cavity behind the detent plunger (where the spring is) fills with oil the oil can get out past the detent plunger allowing for a smooth gear change.
Just a guess

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Find a job you love and you will never have to go to work !

Same thought I had Phil 850

Two groove ones could be from 1970's when everything was groovey.............no idea really.

Are these detent plungers a pain to get out ? Mine are being a bit recalcitrant (PITA). Detent plugs removed, first spings out of each, cant seem to coax them out - drowned passage with wd40, tried pushing with mig wire etc etc. Is there a trick to it ? Mk2 S - 4 speed synchro box completely dis-assembled except for these.

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1970 Mk2 Cooper S under restoration

Got mine out with a piece of wire that I used to push them back and forth and WD gaining half a mm. It seemed to be forever.

Thanks, that’s what I’m finding. mm by mm. Tried a rare earth magnet to no avail. Will persevere.

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1970 Mk2 Cooper S under restoration

Ausmini needs a "Like" button.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

If you ask nicely the current forum “owner” may include that feature while upgrading the system software.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

For anyone with the same problem getting the detent plungers out, see pic. Works a treat. A "like" button would be good because I do appreciate people whom reply with appropriate helpful anwers

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1970 Mk2 Cooper S under restoration

I have found another version of 22G411 detent, Can they be dated?

While you're in this section of the 'box - as a reference - the 3 x springs used in the 3-synchro 'S' were if I recall longer than the normal 2A3647 units used across the entire 'A' series range. The reverse detent spring is standard - so you could compare lengths. The Mk 2 'S' however in your case (according to parts #) reverted back to 2A3647. I haven't noted length differences within the Mk 2 'S' all-synchro 'boxes, however would be good to see whether there was consistency. F