roundcase gearbox explained, please

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stian buksa
Cucciolo - the Lil Pup
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Joined: Mon Oct 12, 2009 11:50 am

roundcase gearbox explained, please

Post by stian buksa »

Im having a weird problem with my -71 GT
Whenever Im engaging 1st gear the bike gives a yank after 1 or 2 seconds, as if the gears suddenly falls into place. It stays in gear all the time.
I've checked the selector box and everything looks ok. The shaft between the selector box and the gearbox is slightly worn, but doesnt give any free play
Now I have split the engine, and to me everything looks ok. But none of the manuals I have states what gears engage when 1st speed is chosen, so I cant really check it out
Does anybody know where I can get an overview over what position the different gears are in in the different speeds ?
Preferably downloadable.

Stian, Norway

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SSD900 Darmah
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Location: New Brunswick, Canada

Post by abmartin »

Hi Stian,

Could it be a clutch problem rather than a gearbox problem? You also should make sure that the gearchange return spring is in good order and the pedal is properly centred. Lurching and hesitating when engaging first gear is not unknown with Ducatis and if it only happens occasionally may not be a cause for serious concern.

1979 900SS
Fredericton, NB

MHR / S2
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Post by machten »

Hi Stian,

So when you say that after 1-2 secs you get a lurch, that sounds to me like you are not quite enaging properly on gear shift. If that is the case, it could well be in your selector box setup. Have you tried adjusting the selector adjustment screw behind the gearshift lever?


Cagiva Alazzura
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Post by wdietz186 »

Sounds like the clutch plates are hanging up on the hub or basket keeping the clutch from engaging fully. This is usually caused by grooves/notches on the clutch drum splines. Take a close look at the components.The push rods through the mainshaft can also hang up too and delay full engagement.If the dogs and the shift forks are in good condition it is unlikely a problem in the gearbox.

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Steve Foster
Parallel Twin
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Location: Sydney, Australia.

Post by Steve Foster »

Hi Stian - in response to your question about getting an overview of the position that the different gears are in see the following article ... io_eng.htm

If you look under the section "Transmission with meshing gear" you'll get a good idea of how the 750 GT gearbox works with the main shaft above the lay shaft.

Hope this helps,
1974 Ducati 750 GT

stian buksa
Cucciolo - the Lil Pup
Posts: 20
Joined: Mon Oct 12, 2009 11:50 am

Post by stian buksa »

Finally finished my rebuild, and it seems that Machten was spot on and the gear selector box was badly adjusted

Works like a charm now :-D

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