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RiderDeAzul

Bike jumping in 5th gear

17 posts in this topic

I finally took apart my bottom end, but I can't really see too much that is wrong, how can I tell if a fork is bent? Here are pictures of the parts I can see that are damaged: ImageUploadedByThumper Talk1455044962.393466.jpgImageUploadedByThumper Talk1455044985.784128.jpgImageUploadedByThumper Talk1455045016.499965.jpgImageUploadedByThumper Talk1455045044.864695.jpgImageUploadedByThumper Talk1455045073.045401.jpg

I am not sure how the shift drum is supposed to look, I'm assuming there are chunks missing, but my buddy thinks it is just poorly cast/machined

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the rounding of the dogs on the gears are the first indicator, and the pads on the shift forks are the kiss of death. See the wear on the pads on the forks? they should be smooth and perfectly parallel with the axis of the fork rod.

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the only critical parts of the shift drum are where the nubs for the shift forks ride, and the spindle ends. the rough casting is normal. Replace the worn shift forks, and the trans gears that have the corners rounded that you can see in pic 1-3

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Pic #1 shows gear facing that is diesenegrating

That gear, and it's common contact gears, need to be replaced.

That is 5th and 3rd, correct? Would those little chips cause 5th gear to slip in and out?

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That is 5th and 3rd, correct? Would those little chips cause 5th gear to slip in and out?

 

No, that's the dogs or the drum, or drum pin, or the forks....or a bent shaft....

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Would one fork being bent that little cause it?

 

The fork(s) push the gears into alignment with  the next ratio gear

If it cannot push the last mm or so, the dog/tab will not be fully engaged, and it can 'pop' out of gear.

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You should or have to replace everything and anything that looks worn in there or you will be back to square one in no time.

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Thanks for the help, one last question, the only place I have to look for wear on the shift drum is in the grooves the forks ride in?

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I would be very surprised if the shift drum was worn. The pin rides on the drum and you would need to check for wear at the point that the gear starts engaging to where the pin rests when engaged.

The more likely location is the gear dogs and the mating slot or the fork end of the shift fork. Make sure you replace the mating gear as well as the gear in the photo.

Ex500's used to have a bad 2nd gear. The gears would wear enough to slip. The fix was a new gear with more undercut to hold the gears together under power.

The shift fork should not have to hold the gears together under power. If they do then they get bent and show wear. The root cause is the gears failing.

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ImageUploadedByThumper Talk1455137309.159808.jpgImageUploadedByThumper Talk1455137338.005050.jpg should I replace the first fork too? Or do you guys think it isn't that bad? I'm definitely replacing the 2nd fork pictured, and the 3 gears that mate together.

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Wow, either the fork is really bent or the gears can rock on the shaft. Look at the bottom of the fork in the 2nd picture. See the wear, that is from the surface of the gear the pad should be riding on. The pad is the small shiny spot that is worn. If you laid a straight edge on that surface it should be perpendicular to the shafts in the transmission. I would guess it's not even close.

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Yes the large shift fork is BAD, replace it and look closely at all three. The wear on the gear dogs is normal, probably not the cause of slipping out or not staying engaged. Check the bearings on the ends of the shafts and shift drum. To save some money you could dress the gear dogs down using a right angle grinder, but if your down time and dollars warrant it, replace the gears that show significant wear. I've seen lots worse that did not pop out once fully engaged.

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Here are two granny's, the dark colored shafts were overheated. The shift forks show normal wear, these transmissions almost never used 5 th gear due to their enviroment.image.jpeg

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