IRS gearbox stuck in 3rd

[tzepesh]

Hello, I would like some hints on how to proceed with a gearbox I have. It seems stuck in 3rd. It is off the car, so I took out the nose cone and all selectors are aligned. However, rotation from input shaft is always transmitted to output shafts (I blocked them to check). As I select any of the other gears (R, 1, 2, 4) the gearbox locks completely (I was considering how the gear shifter controls the selectors, I hope my mind works well ). When I select 3rd it moves as before. It never gets to neutral.
So, what could be the issue? It is quite clear I have to open up the case. I have been avoiding this for a long time due to lack of specific tools, but always was curious to perform a gearbox repair. And I can also break a gearbox to make a jig for forks adjustment.
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'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[Ohio Tom]

3rd gear syncro is jammed onto the gear?

Thrust surfaces are chewed up and locking 3rd idler?

If you can select 4th, then the slider is good.


Sadly, time for a re-build.

[tzepesh]

Yes, I can select 4th and it locks up completely. This is what puzzles me, what I have been reading was about broken forks, but this means that the slider would not go to 4th... So something is keeping 3rd coupled. How? I can not understand, because I even tried to force it and it would not jump out.
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'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration

[tzepesh]

Anyway, I will not use this gearbox, I just had it laying around and I am curious what could be the reason for being locked. But I think I will tear it down sometime and use the case for making the fork adjustment jig. No rebuild on this one, I have two more (an AT on the car, another AH or something to play with, this AO (?) and a 002 to grab some gears from it)
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'74 1303S, L98B Viperngrun (extra glitter), German Look
'64 1200, Sea Blue, under restoration