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wobbly rear sprocket on coaster brake hub

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wobbly rear sprocket on coaster brake hub

Old 01-21-17, 07:01 PM
  #1  
TreyWestgate
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wobbly rear sprocket on coaster brake hub

Does anyone have any experience with the rear sprockets on a shimano single speed coaster hub wobbling or coming loose?.

Mine is starting to do this but the bike mechanic told me that as long as it doesn't slip on me that I'm good.

What is causing this and what are the solutions if it becomes worse?.

I know that the sprocket for these hubs have 3 rivits around the ring so maybe those are wearing down?.

other sprockets such as mtb have more rivits so maybe that means longer life there.

Also they are steel so they could strip down and warp over time.

it hasn't slipped until it does and I would rather not be on it when and if that happened, but you'll never know unless you are the one powering it.

should I be concerned?.

It has some play when I wiggle it with my finger
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Old 01-21-17, 07:24 PM
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Is the sprocket itself wiggling, or the whole driver?

Put another way: do you have play (felt as knocking) at the rim if you grab the top of the tire and wiggle it side to side?

The sprocket's mounting lugs can wear out, but I imagine the sprocket teeth would be severely worn out by the time that happened. It is uncommon for there to be any issues with the sprocket's mount, it's usually play in the hub that needs to be adjusted out.

A coaster brake can absolutely be run with no play in the axle, by the way--just to jump ahead of the train that will (inevitably) come running through here saying it needs play.
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Old 01-21-17, 07:26 PM
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If this bike has only a coaster brake then the possibility of the cog coming loose from the hub's driver is A VERY BIG DEAL As in not being able to stop.


But I'm not entirely sure what the problem is exactly yet. I suspect the term rivits that you use is actually the driver's splines and the cog's tabs. Be at ease that 3 tabs/splines have served millions of riders for, maybe, a hundred years if the cogs is properly attached.


The cog is usually held in place by a clip in the shape of a ring with a split. This allows the clip to be opened slightly while it is slid over the driver body then the clip settles into a groove and the clip closes back down. In an ideal world the cog has a slight slop on the driver. Since there is no real side to side forces acting on the cog this slight slop is no big deal. But if enough force is applied to the side of the cog (like a bent/twisted chain link or significantly out of line cog/chainring) the clip can be forced open and jump out of the groove. If the clip was worn out (not common but can happen) then this is even easier. If the cog location on the driver is such that the clip won't fully settle into the groove then it's slipping out and off is also easier.


While this design is very universal in it's basic layout there is some difference in cog thicknesses and driver widths. I have seen cogs which have been from other brands/versions of hubs installed on the wrong driver and then the clip won't settle fully and will let the cog to come off the driver.


This needs to be figured out ASAP. The worst case is VERY UNSAFE. If the mechanic can't figure this out you should seek one that can fully deal with it. Of course since we're here and you're there we really can't say/help much but to worn you of the need to get this fixed before you find out what the cost of gambling really is. Andy
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Old 01-21-17, 07:31 PM
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Originally Posted by wschruba View Post
Is the sprocket itself wiggling, or the whole driver?

Put another way: do you have play (felt as knocking) at the rim if you grab the top of the tire and wiggle it side to side?

The sprocket's mounting lugs can wear out, but I imagine the sprocket teeth would be severely worn out by the time that happened. It is uncommon for there to be any issues with the sprocket's mount, it's usually play in the hub that needs to be adjusted out.

A coaster brake can absolutely be run with no play in the axle, by the way--just to jump ahead of the train that will (inevitably) come running through here saying it needs play.
The wheel is tight and has no side to side movement.

I think the sprocket is the only thing that has some play.

Also it was recently adjusted and tightened but is now loose somewhat again
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Old 01-21-17, 10:10 PM
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Old 01-22-17, 11:11 AM
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Originally Posted by TreyWestgate View Post
The wheel is tight and has no side to side movement.

I think the sprocket is the only thing that has some play.

Also it was recently adjusted and tightened but is now loose somewhat again
Actually I take that back some, there is an ever so slight knock in the rim if I wiggle the wheel side to side and when I do it makes the sprocket move some as well
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Old 01-22-17, 11:26 AM
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Making machined perfectly , low cost parts is an oxymoron..

when are the parts fit adequate, considering its not an aerospace application?




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