bigfoot Posted January 30, 2007 Report Share Posted January 30, 2007 I have a 2004 GG Pro 300 that developed a down shift problem last weekend. Luckily I was hardly moving and right out side my shed so other that the broken bit no other damage will have been done. Its the broken bit I'm wondering about. I first thought it was the spring assembly just behind the clutch but today work proved that wrong. I now think its in the selector 'cage' as I would refer to it. I've got the engine out completely now as I need to go in to the gear box. I've never done this on a two stroke but am handy enough with the spanners. Should I proceed or get it to a pro? If I proceed what should I be looking for in the way of unexpected problems. Also are there any special tool or tricks required? Thanks in advance. BTW. The symptom I have now with the return spring assembly missing is good upshift but no down shift. In fact I can turn the gear lever all the way round and round in the anti-clockwise direction without even feeling much resistance. Quote Link to comment Share on other sites More sharing options...
lineaway Posted January 30, 2007 Report Share Posted January 30, 2007 Before going any further, I suggest taking it to a good Gas Gas mechanic. You want someone that is familiar with this transmission. Now if you`d rather spend a lot of time on this, the Pro motor is easy to disasemble. You did not mention if the shift spring was broke,and also check the piece that fits over the shaft. The little tab that rides in the end of the shaft can break loose and spin, so check it carefully. Good luck! Quote Link to comment Share on other sites More sharing options...
bigfoot Posted January 30, 2007 Author Report Share Posted January 30, 2007 The spring is OK as is the tab. These parts only ensures the lever returns to centre which it does just fine when fitted. Quote Link to comment Share on other sites More sharing options...
spinner Posted January 30, 2007 Report Share Posted January 30, 2007 The shift shaft center locater and spring is broken. The cases have to be split to replace it, there are 2 springs and roller on the shaft , 1 of them is broken. There is a picture on page 44 of the Gas Gas parts book. Quote Link to comment Share on other sites More sharing options...
windlestone Posted January 30, 2007 Report Share Posted January 30, 2007 been a few posts about this in the past Bigfoot, think the canadian guy that R2W was friendly with posted pics of a gearbox strip down and rebuild. I had an 02 GG that had gearbox problems and it was a top hat bush on the end of the shaft that had snapped then damaged a gear and shaft. Sorry i can't remember the exact procedure Quote Link to comment Share on other sites More sharing options...
bigfoot Posted January 31, 2007 Author Report Share Posted January 31, 2007 The shift shaft center locater and spring is broken. The cases have to be split to replace it, there are 2 springs and roller on the shaft , 1 of them is broken. There is a picture on page 44 of the Gas Gas parts book. This was my diagnosis from looking at the parts book before posting this thread. I happy that you agree but it still begs the main question. Do I go in there myself or do I get a pro to do it? Any help on what to expect or a idiots guide to splitting the case would be good or the name of a man (or woman) I can send it to for a good job and a quick turnaround would be appreciated. Quote Link to comment Share on other sites More sharing options...
toofasttim Posted February 2, 2007 Report Share Posted February 2, 2007 I'm probably speaking out of turn here John, but I've known guys with less ability than you successfully stripping and rebuilding a pro motor. Quote Link to comment Share on other sites More sharing options...
scrappington Posted February 2, 2007 Report Share Posted February 2, 2007 Take a look at this sorted http://d-mis-web.ana.bris.ac.uk/personal/H...f/media/gasgas/ look at engine stripdown number 11 video shows full engine gearbox stripdown Quote Link to comment Share on other sites More sharing options...
cdn280 Posted February 4, 2007 Report Share Posted February 4, 2007 Before going any further read my post. http://www.trialscentral.com/forums/index....8&hl=return The first time I looked at the return spring under the clutch, it looked fine, until I watched what it was doing while pushing on the shift lever. Take it completely off and make sure the key part of the hat the spring sits on is not broken. Quote Link to comment Share on other sites More sharing options...
bigfoot Posted February 5, 2007 Author Report Share Posted February 5, 2007 Before going any further read my post.http://www.trialscentral.com/forums/index....8&hl=return The first time I looked at the return spring under the clutch, it looked fine, until I watched what it was doing while pushing on the shift lever. Take it completely off and make sure the key part of the hat the spring sits on is not broken. I know when the problem is in the box or in the spring! The spring is centring the shift fine. Its just not selecting gears down. I can see from the parts book what the problem is and I just need time to get it done. I'm going in this week so I'll let you see the problem once I get there. As further support for this I can take the spring off (which I have) and the lever still only catches an up change. During an attempted down change I can spin the whole level round and round without it catching on the selector. I got an email from someone on here who explained the job as easy and gave a blow by blow account of splitting the box and its what I thought it would be. BTW He too could tell what the problem was by only reading this thread. Quote Link to comment Share on other sites More sharing options...
peterb Posted February 8, 2007 Report Share Posted February 8, 2007 Hello Bigfoot, I've worked on a few PRO motors. If you can get the crank clutch gear off without too much drama (There is a factory puller that grips the gear OD that allows you to extract the gear without any damage) then the only other tool that is needed is the flywheel puller. Most likely problem is the pawl mechanism on the end of the gear shaft, inside the selector drum. This has 2 pawls that engage the drum when the gear shaft is moved. The pawls have tiny hairspring type springs to keep them loaded out. Sometimes these springs can break, pretty unusual though. The engine is straight forward to work on, getting the kickstart spring back into position can be painfull unless you make up a Tee bar tool with an old kickstart boss to allow you to rotate the kickstart shaft and position the spring at the same time. Use stacks of oil on the gears when assembling as they can stick when trying to set up the selector return mechanism. Use a new crankcase gasket and refill with 10 weight mineral or an ATF rated to Dexron III. I don't know what year your PRO is but there are different crankcase gaskets to fit the 2002 models and then all the later ones. Good luck, Peter B. Quote Link to comment Share on other sites More sharing options...
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