TXT Pro 300, shift drum assembly

[lomker]

Hello, can anyone please help me with this? I have a GasGas TXT Pro 300, 2009 that I am trying to reassemble. I cannot figure out if the shift drum goes onto the shaft first or if I insert it first into the gearbox and then onto the shift shaft. Either way, it seems to be difficult to find the right orientation of the drum. Is there anything I am doing awfully wrong? Any hints would be greatly appreciated.

 

Edited April 8 by lomker

[konrad]

I've never done a GG, but the EFI OSSA gearbox is similar (designed by the same guy).  It's a goofy (patented) mechanism for sure, 4 gear pairs provide 6 ratios.

Here is a service manual for the 2018 bike, which will have a similar transmission setup. See page 48, everything is held in the right hand case-half.

https://drive.google.com/drive/folders/1xOzbrZQDO_W_AxpjvHU1xJMOqfRsVfPJ

Edited April 8 by konrad

[arnoux]

I can help you with this one, (done heaps of them over the years in our workshop)

Remove the Gear Selector Arm spring holding bolt. (In your photo it is the M6 bolt that the curved end of the spring sits against. in a little grooved bush under the bolt head. Part number T305020). Then you can let that Gear selector arm swing to the left.

Now you can assemble the drum down onto the shaft. Put it on 180 degrees to the way you are holding it in the second photo. That open cavity faces down, and those two little rollers on the shaft you will probably have to sqeeze in a bit with a little pick or screw driver to get it to go all the way down. Those little rollers then sit in those little cutaways you can see on the inside of the drum.

Then rotate the drum until the neutral indent (see the "star point" that has the curved relief in the middle of one of the "points" line up with that Gear selector arm roller you previously looosened). Then put the M6 srew back in so there is that tension on the arm holding that roller in place in that Neutral indent. It is easily achieved using a big phillips head screw driver to pull the spring around. There is a perfect hole under the spring to put the screw driver in , lever the spring around and fit the bush and screw.

It is important you set this to Neutral as it makes getting all the gears and forks back onto the shaft possible in the next step.

[agiow]

The selector drum slides over the gear change shaft indicated by the red line

The two rollers indicated by the two blue arrows are located on the internal profile

of the selector drum indicated by the 3^rd blue arrow.

The single roller hi-lighted by green arrow locates on the outer profile of the selector drum

And it locates in a small concave cut-out indicated by the other green arrow.

This gives the correct position of the selector drum.

Hope this makes sense, It’s a little fiddly.

I would put the drum on the shaft first then fit the shaft to the gearbox.

[lomker]

Thanks to arnoux, and also konrad and agiow, that was a perfect description and it helped a lot. The drum is on the shaft and hopefully in neutral. Now I am fiddling with the gears and fork to go back in as well. 

Edited April 9 by lomker