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Discussion Starter · #1 ·
For reasons that are not important here, I had the bike on a jack with it running, in gear to spin the rear wheel.

Though the bike was balanced on the jack, it would occasionally bob to the rear, dipping 1/2" or so.

This did not seem right. It should sit there steady, as long as the rpms stay the same and the resistance on the drive-train stays the same.

Eventually, I felt the hub and it seems that is the source of my inconsistent resistance.

So, I pressed my ear up against it and could clearly hear a periodic thud timed exactly with the bob of the bike.

I drained the hub oil and examined the teeth you can see through the fill hole. All were perfect, so I can only assume the opposing teeth are fine as well. This is confirmed by the irregular timing of the thud, which has no particular correlation to wheel rotation.

This leads me to believe that it could be the hub bearing, spinning, but imperfectly, sticking periodically.

I put new oil in and buttoned it back up. I am crossing my fingers that it was just some debris in there that the fluid change will resolve, but I'll get a better feel for that after I get a ride in tomorrow.



Thoughts from anyone who has been in there?
 

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I would be checking the driveshaft where it goes into the rear drive. I've had some trouble with mine-see the post ref driveshaft problem
 

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For reasons that are not important here, I had the bike on a jack with it running, in gear to spin the rear wheel.

Though the bike was balanced on the jack, it would occasionally bob to the rear, dipping 1/2" or so.

This did not seem right. It should sit there steady, as long as the rpms stay the same and the resistance on the drive-train stays the same.

Eventually, I felt the hub and it seems that is the source of my inconsistent resistance.

So, I pressed my ear up against it and could clearly hear a periodic thud timed exactly with the bob of the bike.

I drained the hub oil and examined the teeth you can see through the fill hole. All were perfect, so I can only assume the opposing teeth are fine as well. This is confirmed by the irregular timing of the thud, which has no particular correlation to wheel rotation.

This leads me to believe that it could be the hub bearing, spinning, but imperfectly, sticking periodically.

I put new oil in and buttoned it back up. I am crossing my fingers that it was just some debris in there that the fluid change will resolve, but I'll get a better feel for that after I get a ride in tomorrow.

Thoughts from anyone who has been in there?
It's normal. When the motor is @ a constant RPM and the drivetrain has near zero-load, the rear tire has to "catch up" at intervals due to backlash @ all the gear mating surfaces throughout the drivetrain. The lighter the rear wheel, the more frequent the interval. The larger the total backlash throughout the drivetrain, the more severe the reaction. Try doing the same on a chain driven bike with excess chain slack to see what I mean...
 

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Discussion Starter · #4 ·
It's normal. When the motor is @ a constant RPM and the drivetrain has near zero-load, the rear tire has to "catch up" at intervals due to backlash @ all the gear mating surfaces throughout the drivetrain. The lighter the rear wheel, the more frequent the interval. The larger the total backlash throughout the drivetrain, the more severe the reaction. Try doing the same on a chain driven bike with excess chain slack to see what I mean...
I love that answer because it means I do not need to rip the hub apart with just days before the Mid-Atlantic meet.

I'll keep my fingers crossed that your explanation is right.
 

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I love that answer because it means I do not need to rip the hub apart with just days before the Mid-Atlantic meet.

I'll keep my fingers crossed that your explanation is right.
You can observe that total backlash by jacking it up, motor off, in gear... then move the rear tire/wheel forward and backwards. You do need backlash, but too much is just as bad as none at all. Lamonster made a post with a video back in 2006 or 2007 that showed what too much total backlash looks like. I measured what a good amount was... just forgot where the post is. :-\ I doubt you have anything to worry about unless you've been doing hard launch drag racing more than street riding or had your final drive taken apart and put back together incorrectly. :bigthumbsup:
 

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SR, I've seen mine do that too, so I'd say the pup is right.

My GiPro wouldn't correctly recognize the gears when I first put it on so I had to go through the manual learning process with it. Rather than try to do that while going down the road, I put it on the bike jack and went through the procedure. At idle mine did the same as yours.

I wouldn't recommend doing the learning procedure that way either, in case someone reads this. By the time you get it in 5th gear at almost any engine rpm that rear tire is moving. I'm probably lucky I still have a back wall in my storage building, as it would bob down under each gear change and was probably coming close to getting a grip on the pavement.
 
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