broken gear, need some opinions

so i recently bought a 2010 from a friend, was familiar with the bike, he changed fluids regularly, rode track maybe once a month or so and never had any problems with the bike except the occasional hard start. i was cruising down the beach one day, not riding too hard when i shifted from 3rd to 4th and felt a nasty clattering sound and the bike started to buck (felt like a few teeth had broken off a gear). i tried to shift to 5th and nothing, like neutral, went back down to 3rd to try and get home then the bike died. drivetrain was locked even in neutral and the kick starter wouldn't budge, my first thought was broken gear. brought the bike to a friend who has a lot of experience working on bikes and all types of motors, he confirmed my assumption, 2nd driven gear on the counter shaft broken in half. all bearings, shafts, case and other gears showed no signs of damage except for normal wear on the dogs and very minimal grind marks on the case where the broken gear was tumbling around (which surprised me, i thought it would be a lot worse) so i ordered a new gear and bushing and installed it myself according to the service manual, put the cases back together and turned the crank by hand to check that the gears were shifting normaly, all was smooth and i double checked everything since it was my first time dealing with a tranny. got the motor back in the bike to take it for a test ride, hard as hell to start but i got it eventually. gears shifted like normal from 1st to 3rd but as i clicked up into 4th, bam! same clattering and bucking like the first time. i havent had time to split the cases to investigate yet but i'm 99% sure its the same gear that broke again. the only thing i can think of is that one of the shafts was damaged from the first time and is restricting the 2nd driven gear a bit so that when torque is applied ît just snaps. where i live there are no proper bike meachanics and the few that are around are expensive and take forever to do jobs so i am trying not to go that route. i'm thinking to replace the entire transmission, shift drum and forks. if anyone can give me a some insight/opinions/recomendations it would be greatly appreciated

PS. great forum btw, lots of info available

hard to tell untill you check the problem again... it might be something else.

suzukis of 09-12 had lethal gboxes. 

i've come to realise this. try to work on it this weekend

good luck with it.... there were threads on here about the problem. people had to get new gears and send them off to be coated and hardened... i think ron hamp does this.

longer "hammer head" gear lever and a rm450 detent spring will also help with the gbox mis shifting.


but with your "exploding" gbox, there might be something else.

i've come to realise this. try to work on it this weekend


Hey MdMX get it split open. did you check the shift forks? if i recal correctly shifting from third to fourth requires two operations from the forks at the same time, if one fork is bent this can cause problems. you should check the assembly of the gears as well, and thoroughly inspect any thrust washers,circlips and the drum itself. take pictures and post if you can they help a lot in diagnosing problems... 


oh yes i forgot, its good practice to replace neighboring mechanisms. second driven is engaged with a sliding dog if i remember correct so that should also be replaced

Edited by funkinalive

yeh agree with funkin, sounds like two gears at the same time

sorry for my VERY late reply, good news though, I GOT THE BIKE WORKING!!!

turns out that no gears were broken this time but there was some very bad damage to the dogs on 3rd driven, so i replaced that along with the bushing and the two oil pumps (which were stuck with debris from my first episode) and wala. bike works like (almost) new! runs like a beast, gears shift smoothly and i am once again a very happy rider :D

still debating if to sell it and go back to blue bikes (my first love) but b4 i do i will definetely be riding my moneys worth out of the zuki, spent too much time nursing her back to health not to

thanks again for your help and opinions and wonderfull site of dirtbike knowledge


just thought i should add everything i replaced:

2nd driven

3rd driven

sliding dog between the two^


shift forks and fork shafts

complete oil pump assembly

i realised why i was getting a hard start b4, because the oil pumps were ceased it was creating resistance when the engine was tumbling, they were actualy so stuck that i wrung out the shaft connecting one to the other.

i must say for my first experience completely overhauling a motor i've gained a whole lot of know how :D

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