I haven't see the diagrams you are looking at but found this one for a rod change transmission.

https://www.minimania.com/catPage/4-23/4/23/0/Rod-Change-Gear-Selections--Speedo-Drive

It is different to what I recall about the remote shift box I dealt with.
In this case, it appears the shifter forks 17 and 18 slide on the selector shaft 16 and the upper and lower bell lever cranks 12 and 13 remain engaged with the forks. The selector shaft 14, which protrudes from the box and is connected to the rod change mechanism has a pawl on the end which selects 12, 13 or 10 (reverse release lever), depending on what you choose.

Not what I expected! For comparison, here is what I was thinking about
https://www.minimania.com/catPage/4-21/4/21/0/Magic-Wand---Remote-Type-Selections--Speedo-Drive
The miserable bolt I was writing about is 13 in this diagram>

It might be wear on 12, 13 and 14 or the stack of parts on the bell crank pivot pin 7. Maybe the linkage is not returning the 3-4 bell lever crank to the neutral, disengaged position.

Soo going to take this gearbox out this weekend. I thought I would look at a couple of drawings so I can see what I am in for.  It looks like my rod change box the shift cradle is held in with a roll pin and not a set screw.  The only lock nut that is in that area is the one holding the shift selectors on.

The gearbox you guys are referring to is that a different model?

Thanks!

From what I recall, I could see the bolt and its angle with the diff removed. That meant I could get the hole position and angle right. I could also get the fork in the right location on the rail (shaft) and the bolt into the detent. You may be right about the locknut... if there was one. Too long ago to remember. I did drive it for a yer or two without issue. I sold the Mini after I bought a brand new 1974 Fiat X/1-9  for about $5,000 CDN. Cars were cheaper then! A new Mini was going for about $2000.

Then there was the time I fixed a HS4 with a resistor from Radio Shack. But that's another story.

I also give Dan 2 thumbs up for getting it back on the road ASAP, but I think his solution might not have worked for me.  In Dan's case, his drilled hole happened to line up with the fork and the shift shaft happened to also be lined up ready for the pointy end of the setscrew to hit the detent when he tightened it. I dont think I have ever been that lucky.  (Dan, buy me a lotto ticket this week, OK?)  Also, his socket did tighten the setscrew, but not the locknut. So it would work for a while, but then driving it I would be sweating like a nun in a cucumber patch.

Dan: "...Not having the tools, experience or workspace to rebuild the transmission, I developed "Plan B". By removing the diff, I could see the loose bolt but could not get a wrench on it. Figuring the position and angle carefully, I drilled the transmission case to allow the right sized socket wrench in to tighten that sucker. Then I tapped the hole and installed a galvanized plumbing plug. Job done. ...."

FANTASTIC Dan.  Just fabulous thinking.

2 thumbs up ! 

I think Scooperman has it right.

I bought my second Mini, a 1969, for $300 (it was 1974) because the lump was out of it and the transmission had a similar shifting problem. It also needed a clutch. The manual advised that the LAST pieces to come out of the gearbox was the shifter fork and rail. Not having the tools, experience or workspace to rebuild the transmission, I developed "Plan B". By removing the diff, I could see the loose bolt but could not get a wrench on it. Figuring the position and angle carefully, I drilled the transmission case to allow the right sized socket wrench in to tighten that sucker. Then I tapped the hole and installed a galvanized plumbing plug. Job done. When the slipping clutch got too annoying I did take it to a shop.

The gear box is a rod change, could this still be the issue?

workinprogress has it right. The shifter fork set screw has a locknut, the locknut got loose and the screw backed out of the 3/4 fork detent in the shift shaft.  There was enough shaft friction to get it in gear one more time, but getting it out of gear not enough friction to pull the synchro out when the shaft moved over.  There is a tiny chance that after everything gets cold you could get it out of gear while all the pieces are sitting still.  Deceleration under load is another maybe, so jack up the hubs and run it, then see if the gods are with you, maybe it will pop out when you move the shifter out of 4th just as you take your foot off the gas.  If you do get it out of 4th, drive it in first and second if you really have to move it, but stay away from 3rd and 4th until you pull the lump and fix it.  Happened to me in my 850 Countryman, drove 30 miles on backroads in 1st and 2nd to get home.  Now I drill the screw heads and the forks for safety wire as the factory should have done.

What transmission? If remote most likely the set screw that holds syncro selector to shifter rods inside. 

Hello All,

After some rough driving my mini got stuck in 4th gear.  Came back jacked it up and moved the shifter linkage in and out several times and it seemed to have freed it up.  Drove it again and once again stuck in 4th. When when the shifter is  in neutral the trans is still stuck in gear. When I press the clutch that seems to be working correctly

Any ideas on what could cause this before I go ripping everything apart?

Thanks in advance!