Very Strange Transmission Problem: gearbox sticks in 2nd!!

[Killermiller]

Hi Everybody,
I hope to let you all understand the problem, since English is not my native language and the problem is a bit odd. 
I'm experiencing this strange problem with my 126 BIS: after I partially rebuilt the transmission (I made a working one out of two defective ones with brand new bearings), every now and then, and always after a stop, I can't take it out of second gear. The selector just goes out of its place on the 1st & 2nd selector rod and, of course, once out of its place, it will be impossible for it to "pull out" the second gear. Once crawled under the car, removed the rear cover and pulled manually the trans out of 2nd, everything will be fine. The car will run smooth and fine, until it will randomly happen again.

No, I didn't forget to put the two little egg-shaped keys (the ones that that will prevent two gears to engage simultaneously) in place, on top of 1st-2nd and 3rd-4rd selector rods respectively. Also, the three springs and detent balls are in place.

After swapping the selector and the cover with other known good parts, and being finally tired of crawling under the car to remove that cover, with gearbox oil dripping on my face, I took the transmission out. Now it's on my bench, still in one piece. What should I check?

[Gadge]

It may well be the linkage? It's adjustable at the gear stick side. There's two bolts on the drivers side (RHD) transmission tunnel. If you slacken them put it into 1st then tighten them up it should give you a better selection

[1973/126]

 I had exactly the same problem with one of my gearboxes, but never got to the bottom of the problem. Once you selected 2nd gear it was just stuck in and you couldn`t get it out. I just ended up replacing it for another box.
 I was wondering if it could be something to do with synchro failing.

[Killermiller]

Thank you very much for your replies and advices.
I've just reinstalled the transmission, after replacing both the selector and the 1st - 2nd gear rod. Looking at the gearbox on the bench, without the cover, I've realized something I didn't before: it would be impossible for the selector "tail" to slip out of the groove on the selector rod with the 2nd gear engaged. This means that, for some reason, the 2nd slips in by itself, while the gearbox is in neutral. Once in 2nd with the selector in neutral, meaning OUTSIDE of the groove on the rod, it will be impossible for the selector to reach the groove on the rod and pull it out (and that's why it stays in 2nd).
Also, when I push the 2nd fork by hand, 2nd engages with less effort than 4th or reverse. This strenghtens my suspect and might mean that:

1) The groove on the selector rod (the one where the detention ball goes) is worn. I've replaced the rod, so this should have fixed the problem 
2) The spring that pushes the ball against the rod has lost some strenght. Relatively easy fix this one, because they can be replaced with the transmission almost in place.
3) Most probably, a combination of 1) and 2)

I've test-driven the car and so far, so good. I'll keep you updated. In the meanwhile, any advice or comment would be greatly appreciated!

[Killermiller]

So, hoping this will help others, it seems that changing the first - second gear selector rod has cured the problem. The car runs smooth and fine and the 2nd gear problem didn't show up again since then, although the usual primary shaft teeth begin to show signs of wear. Also, I've replaced the gearbox shaft bushings (the one in the crankshaft, in the middle of the flywheel, and the opposite one, in the gearbox, together with its oil seal) and this solved another very annoying problem I had with the car: shaking transmission on 1st gear clutch release.
A new crankshaft rear oil seal has been installed, also, since I was at it, having the flywheel removed in order to replace the bushing inside the crank (which, by the way, has been a real pain to remove: I had to use a pneumatic chisel to destroy it). A new transmission oil filler plug (the old one had rounded edges and I had to drill it) and new GL3 spec. 80w90 transmission oil completed the job.