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Shimano nexus missing anti rotation washers

Old 04-30-22, 09:22 AM
  #1  
rich110
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Shimano nexus 7 missing anti rotation washers

I have a sunrunner ebike that I recently bought 2nd hand. I loosened the axle nuts to move the wheel back to allow me access to the roller brake grease port then tightened it all back up. When pedaling I felt the hub slip so checked and it had rotated.

The bike doesn't have any anti rotation washers and seems to just rely on the grip of the washer to the frame (axle nuts were incredibly tight before I started work on it). I assumed the drive side had a silver nexus anti rotation washer but it's just some silver flat washer.

Can someone confirm I need a 6L and/or 6R washer?

Dropouts are 10mm wide, axle flats are 8mm, it has what looks like a lock washer with 17mm flats that actually sits inside the dropouts.







Last edited by rich110; 04-30-22 at 10:11 AM.
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Old 04-30-22, 09:56 AM
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The people that made your bike should know... I hope.

I'd ask the bike manufacturer if it was intended to have them and they were left off by someone. If they don't respond to your inquiry, then just leave a review for that bike and tell everyone that the manufacturer doesn't answer questions that customers have.

Certainly I'm not saying to leave a flaming review, however this is the sort of information that I look for when I consider user reviews. Flaming reviews get ignored as do overly raving reviews with little detail about why they like the product so well.

Last edited by Iride01; 04-30-22 at 10:01 AM.
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Old 04-30-22, 10:15 AM
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Originally Posted by Iride01 View Post
The people that made your bike should know... I hope.

I'd ask the bike manufacturer if it was intended to have them and they were left off by someone. If they don't respond to your inquiry, then just leave a review for that bike and tell everyone that the manufacturer doesn't answer questions that customers have.

Certainly I'm not saying to leave a flaming review, however this is the sort of information that I look for when I consider user reviews. Flaming reviews get ignored as do overly raving reviews with little detail about why they like the product so well.
Sorry I forgot to mention it is second-hand; the bike is probably 10-15 years old and I don't think the manufacturer make bikes any more, they make mobility scooters. I guess I could still ask.
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Old 04-30-22, 08:43 PM
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Nexus hubs *require* anti-rotation washers, as substantial torque is applied to the axle unit even without supplementary electric motor power. I would not ride the bike until you get the right anti-rotation washers installed. Serious harm may happen, or at least you may have your shift cable ripped out as the hub slips.

You can see the different washers HERE. If you position the wheel in the frame so the cassette joint (the thing the shift cable enters at the rear hub) is pointing in the right direction*, you may be able to observe the relationship of the axle flats to the dropouts and deduce which washers to get. You could also take the bike to a shop that services Nexus hubs and let them help you select the right washers.
*Generally, the cassette joint should be oriented so the shift cable points in a generally forward direction, and stays clear of the chain.

Last edited by sweeks; 04-30-22 at 08:46 PM.
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Old 04-30-22, 09:25 PM
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Doesn't this model have a brake arm that fastens to the chainstay?

https://si.shimano.com/pdfs/si/SI-75E0E-000-ENG.pdf

https://si.shimano.com/pdfs/ev/EV-FH-IM70-2206B.pdf
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Old 05-01-22, 04:38 AM
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The hub is a 7 speed SG-7R46 and the service manual shows the 2 non-turn washers
https://www.avantum.bike/downloads/S...peed%20Hub.pdf

The roller brake arm is attached to the frame.

is 10mm the standard dropout size for the non-turn washers?

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Old 05-01-22, 07:20 AM
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Originally Posted by WizardOfBoz View Post
Doesn't this model have a brake arm that fastens to the chainstay?

https://si.shimano.com/pdfs/si/SI-75E0E-000-ENG.pdf

https://si.shimano.com/pdfs/ev/EV-FH-IM70-2206B.pdf
The brake arm does nothing to prevent the axle from rotating. It simply anchors the brake.
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Old 05-01-22, 12:58 PM
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FWIW, the clip on the chain's master link is usually recommended to be installed with the closed end in the direction of chain travel. Yours is installed backwards in the second image in Post #1.
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Old 05-01-22, 07:33 PM
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Originally Posted by Dan Burkhart View Post
The brake arm does nothing to prevent the axle from rotating. It simply anchors the brake.
Thanks, Dan. But I look at this thinking of a "free body diagram". (You may know this approach better than I do, pardon me for explaining). So I look at the axle. It's separated from the hub's torque by bearings. The hub has on one side the freewheel and sprocket(s) and is separated from the axle, with little torque transmitted, by the same bearings. The roller brake assembly has its inner part fastened to the hub on the ND side, and this part rotates (normally with no torque tranmitted to the outer part of the brake because of a bearing. The outer brakepart is attched to the inner part by a bearing, and to the frame by the brake arm and clip. No braking? No torque on the outer brake part. Braking? The inner and outer brake parts transmit torque to each other, and the inner part transmits torque to the hub, but I can't see where torque gets transmitted to the axle.

My first Scwhinn Typhoon had a similar arrangement. The brake arm handled the torque. The axle nut was just a regular nut, with a washer.

Is there something in these hubs that transmits torque to the axle?
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Old 05-01-22, 10:50 PM
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Originally Posted by WizardOfBoz View Post
Thanks, Dan. But I look at this thinking of a "free body diagram". (You may know this approach better than I do, pardon me for explaining). So I look at the axle. It's separated from the hub's torque by bearings. The hub has on one side the freewheel and sprocket(s) and is separated from the axle, with little torque transmitted, by the same bearings. The roller brake assembly has its inner part fastened to the hub on the ND side, and this part rotates (normally with no torque tranmitted to the outer part of the brake because of a bearing. The outer brakepart is attched to the inner part by a bearing, and to the frame by the brake arm and clip. No braking? No torque on the outer brake part. Braking? The inner and outer brake parts transmit torque to each other, and the inner part transmits torque to the hub, but I can't see where torque gets transmitted to the axle.

My first Scwhinn Typhoon had a similar arrangement. The brake arm handled the torque. The axle nut was just a regular nut, with a washer.

Is there something in these hubs that transmits torque to the axle?
Yes. The Nexus internal gear hub uses the rear axle as a sun gear for its planetary transmission. In anything except the 1:1 middle gear, the axle is turned with considerable force. The axle has flats that fit in the dropout slot but that's not enough to prevent damage. Shimano (and Sturmey-Archer) have washers that spread the load and resist the axle's rotation in the dropout.

Your Schwinn Typhoon probably had a coaster-brake or perhaps a Bendix two-speed kickback hub. I believe the torque arm did double duty on the kick-back hub because the sun gear/adjusting cone was locked to the axle.

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Old 05-02-22, 05:17 AM
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Originally Posted by rich110 View Post
The hub is a 7 speed SG-7R46 and the service manual shows the 2 non-turn washers
https://www.avantum.bike/downloads/S...peed%20Hub.pdf
The selection of the correct non-turn washers has to do with the position of the cassette joint when the wheel is mounted. You don't want the shift cable running into the chain.
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Old 05-02-22, 05:22 AM
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Originally Posted by WizardOfBoz View Post
Thanks, Dan.
Is there something in these hubs that transmits torque to the axle?
There sure is. The sun gears are reactionary gears affixed to the axle. In underdrive gears, the torque will act on the axle in a rearward direction. In overdrive gears, the force is in a forward direction. The axle must be braced against this rotation force.
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Old 05-02-22, 07:05 AM
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Thanks, Dan, Jeff and Rich110 for the info. I'd seen the Nexave label and assumed that the hub was a Nexave and not a Nexus. Clearly the pictures show that it is an IGH and not a freehub! Thanks for the education, guys.

So the OP needs a 5, 6, or 7 L and R anti rotation washer set. These vary according to dropout angle. See page 20 of this document. 5 size washers for angles of 20 or less, 7 size washers for 20-38, and 6 size washers for 0.
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Old 05-02-22, 12:59 PM
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thanks for the help guys.

If I put a NTW washer on first, the chain tensioner adjusters won't work/fit because they will be too far out. They only work if they are placed on the axle first.

The NTW are 6mm wide. I placed the 3mm washer on the inside in this pic to demonstrate. Can i just remove the chain adjusters completely?

6R 6L is what I will try and get



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Old 05-02-22, 01:58 PM
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Originally Posted by rich110 View Post
thanks for the help guys.

If I put a NTW washer on first, the chain tensioner adjusters won't work/fit because they will be too far out. They only work if they are placed on the axle first.

The NTW are 6mm wide. I placed the 3mm washer on the inside in this pic to demonstrate. Can i just remove the chain adjusters completely?

6R 6L is what I will try and get



Chain tensioners for rear facing dropouts are nice to have, but not crucial. The anti rotation washers are .
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Old 05-02-22, 09:02 PM
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Originally Posted by WizardOfBoz View Post
The roller brake assembly has its inner part fastened to the hub on the ND side, and this part rotates (normally with no torque transmitted to the outer part of the brake because of a bearing. The outer brakepart is attached to the inner part by a bearing, and to the frame by the brake arm and clip.
The inner brakepart, (I like this term!) comprising the cam, the rollers, and the shoes, is attached to the axle by a 17mm nut, and stabilized by the torque link. The cam is able to pivot on the axle in order to push the rollers and shoes radially. The outer brakepart, comprising the drum and heat sink, engages splines on the NDS of the hub and rotates with the hub. When the brake is actuated by rotation of the cam (by a lever), the shoes are forced radially outward to contact the drum. The torque on the shoes resulting from contact with the rotating drum is fed through the torque link into the bike frame. This is essentially independent of the forces acting on the axle from the internally-geared hub.
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Old 05-05-22, 12:15 PM
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Does it matter which way the washers face?

Even if I lengthen or replace the chain, the brake arm that attaches to the frame is already as far back as it will go! There is no way I can place the washers facing the inside of the dropouts without extending the brake arm somehow.

Are they OK facing backwards?






In the workshop manual for the newer roller brakes (p12) it shows the NTW facing the open end of the slot. for a horizontal dropout it shows it facing the inner part of the slot. I assume that is because of the chain adjusters?




edit: nm found it

Last edited by rich110; 05-05-22 at 01:23 PM.
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Old 05-07-22, 05:35 AM
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Originally Posted by rich110 View Post
Does it matter which way the washers face?
Are they OK facing backwards?
The purpose of the washers is to prevent the axle from rotating. This is achieved as long as the tab engages the slot. Either way is fine.
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