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Shimano internal gear hub help

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Shimano internal gear hub help

Old 04-18-19, 12:30 AM
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Shahmatt
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Shimano internal gear hub help

Hi all, I have a problem with a Shimano Nexus 7 sg-7r46 hub which I would appreciate any advice on.

I've been using this hub for a while. In the old configuration the hub was linked directly to the chain ring, but now I've added a rear tensioner so that I can work with different chain rings.

The problem is that if I apply weight to the axle (i.e. sit on the bike) the cog does not turn freely in the reverse direction. A resistance builds up on the rear cog rotation.

The resistance shows when I cock the pedals for take off at a traffic light. I turn the pedals backward and the tensioner gets pulled up. This sometimes dislocates the chain.

I'm guessing the resistance also applies to forward movement, but it is small enough to affect the ride.

I have greased the hub previously (before the tensioner) so I know the internals are working smooth. I do not recall seeing anything amiss.

Does this problem sound familiar? Is this the natural behavior of the hub? Any advice is much appreciated.
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Old 04-18-19, 07:13 AM
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Broken axle?
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Old 04-18-19, 07:23 AM
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Dan Burkhart 
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What I often see with these hubs is friction between the sprocket and dust cap causing the exact symptoms you describe. If you remove the sprocket, thoroughly clean and lightly lube the contact area, you may find some improvement.
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Old 04-18-19, 10:14 AM
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Originally Posted by Dan Burkhart View Post
What I often see with these hubs is friction between the sprocket and dust cap causing the exact symptoms you describe. If you remove the sprocket, thoroughly clean and lightly lube the contact area, you may find some improvement.
Thanks Dan for your advice. On a previous occasion I had to replace the rubber dust cap because it was distorted and rubbed against the cog. I wonder if it has distorted again ever so slightly to cause to this to happen. I will try what you say and see what happens.
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Old 05-13-19, 01:51 AM
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Shimano Nexus Hub 3 speed automatic, Bianchi "Auto-Milano"

Originally Posted by Dan Burkhart View Post
What I often see with these hubs is friction between the sprocket and dust cap causing the exact symptoms you describe. If you remove the sprocket, thoroughly clean and lightly lube the contact area, you may find some improvement.
Hi Dan,
Saw your post for the hub problem, and just wanted to know if you have any experience with an automatic 3 speed version of this Nexus hub. It is mounted on a Bianchi "Auto-Milano" cruiser style bike. Asian made with all shimano, but cheap, except for this transmission which has a digital controller for opting "automatic or manual" shifting. I've yet to ride since I'm not that type of rider. Bought for $45 as a "guest" bike figuring it would be easy for a novice rider with the auto-shifting. Anyways, I'm curious if they had any problems; can't figure why they got rid of a fairly expensive bike that was barely ridden, and I don't want to cause more damage if hub is faulty; priced hub at $400 NOS. I figure if the hub is faulty for some reason I can make it into a basic 3 speed, or single speed. Has odd shimano rear drum/disc brake in the rear. I'm a road bike guy so this is all foreign (no pun!) to me. I just don't want to have problems on a ride with some one if this unit tends to have problems. Thanks for your time. Bike is somewhat buried behind other frames so I haven't a photo yet, but will get one posted in the next day.
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Old 05-13-19, 05:19 AM
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The longer the derailleur arm is the less leverage the spring has. The spring tension is insufficient.

Switch to a short cage derailleur. Short cage derailleurs hold the chain under higher tension.

If it helps visualize: We are dealing with levers & fulcrums.

Oh, & make sure your stops are adjusted properly to hold the alignment. Ocassionially that means a longer screw from the hardware store.

Last edited by base2; 05-13-19 at 06:26 AM.
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Old 05-13-19, 05:22 AM
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Originally Posted by HPL View Post
Hi Dan,
Saw your post for the hub problem, and just wanted to know if you have any experience with an automatic 3 speed version of this Nexus hub. It is mounted on a Bianchi "Auto-Milano" cruiser style bike. Asian made with all shimano, but cheap, except for this transmission which has a digital controller for opting "automatic or manual" shifting. I've yet to ride since I'm not that type of rider. Bought for $45 as a "guest" bike figuring it would be easy for a novice rider with the auto-shifting. Anyways, I'm curious if they had any problems; can't figure why they got rid of a fairly expensive bike that was barely ridden, and I don't want to cause more damage if hub is faulty; priced hub at $400 NOS. I figure if the hub is faulty for some reason I can make it into a basic 3 speed, or single speed. Has odd shimano rear drum/disc brake in the rear. I'm a road bike guy so this is all foreign (no pun!) to me. I just don't want to have problems on a ride with some one if this unit tends to have problems. Thanks for your time. Bike is somewhat buried behind other frames so I haven't a photo yet, but will get one posted in the next day.
No, I have never dealt with the automatic model.
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Old 05-13-19, 08:42 AM
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Shimano Nexus

Originally Posted by Dan Burkhart View Post
No, I have never dealt with the automatic model.
Thanks Dan,

It was a shot in the dark. Apparently these bikes are kind of hard to come by with the auto transmission. I'm going to toss on a couple new tubes and see if the thing functions or not. Should be interesting to compare with my 69 Raleigh Sports for shifting and ratios.
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Old 05-13-19, 08:47 PM
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Does the hub jam if you put it back the way it was without the tensioner?

Could be an alignment problem in the tensioner.
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