benshares

A local farm asked me if I could take a look at their cargo bike whose "bottom bracket is slipping" - I am not a serious wrench, just built a few single speeds and road bikes, but I like learning and I like a challenge, so I said I'd take a look.

Whew.

I've created a little gallery of photos here: https://photos.app.goo.gl/Hm6jtKmdoLAHzEAG2



Basically it's got a Shimano Nexus 3 speed internal gear hub. The main issue I could see is that the piece of the transmission that anchors the hub to the frame is missing, and the arm spins along with the wheel as soon as you try to brake, turning it into a weird sort of fixed gear. It also seems like using the brake (or pedaling too hard) causes the bolts that hold the wheel on to unscrew? Everything was loose when I first checked out the bike. The shifter that attaches to the hub also just pulled off with a light pull, no tools.

I tried to zip-tie the frame arm to the frame to see if that would fix it, along with tightening the bolts down, but braking tore the zip ties off and loosened the bolts, so I'm really not sure. I

I'm not sure if I should seek a more permanent attachment for the frame arm to the frame, or just try to replace the hub/wheel with a newer (simpler?) one.

Thoughts?

FBinNY 

There are two sets of parts that you need.

You have to secure the "reaction arm" to the frame because that's what the brake engages to stop, and if not attached it'll spin instead of slowing the bike.

Also, the axle need the keyed "anti-rotation" washers that keep it from spinning in the dropouts. The axle acts as a lever fulcrum, with the internal gears pushing off it. If not keyed, the pedaling torque will tend to turn the axle and loosen it.

It's possible that the brake reaction arm also holds the axle, but it's attached to the cone, so unless the axle is keyed to the frame, you risk unscrewing the cone, and loosening everything as you ride.

Once both the brake arm and axle are secured so they can't turn, the nuts won't loosen anymore.

Start there, and solve that problem, so you can properly test ride the bike and see what, if anything else is wrong.


BTW - Local Farm??? in Brooklyn????

CliffordK

If you look for a junker coaster brake kid's bike, you should be able to find that strap for the reaction arm. Or make one with plumbing pipe hanger strap... or use your imagination.

I took apart a Sachs Dual Drive hub, and it was surprisingly simple to take apart and lube. Perhaps this would be a good time to do some hub maintenance.

You have a lot hanging off of those axles, but as FBinNY suggested, make sure you have the anti-roation washers on the axle, and in good shape. I'd be tempted to remove the basket until you get the hub straightened out.

FBinNY 

One more note.

If you linked the image of the keyed washers, you may have noticed that they come in various orientations for the axle vs. the tabs.

You have to rotate the hub so the brake arm is in the right place under the chainstay, then remove the axle nut and look at the orientation of the axle's flats with respect to the dropout slot. You have to match that when you buy the washers. Note, that on a frame like yours, you might be able to have the tab either in front of the axle or behind, and have two orientations for the angled washers if you flip left for right.

Dan Burkhart 

that is true for 7 8 and 11 speed Shimano IGH but not for three speeds. the axle does not care how it's oriented, only that it is braced against rotation.
Also, Nexus three speeds only use one anti rotation washer, and it's on the non drive side.

FBinNY 

This bike has a coaster brake. I'm not sure if the axle can turn with respect to the reaction arm. Of course even if it can't, the left cone can be loosened and the axle rotated to whatever orientation that one wants. But seeing how the OP has limited skill, I suggested getting keys to match the axle and frame, rather than adjusting the axle to match the key and reaction arm.

dedhed

https://bike.shimano.com/media/techdo...9830704663.pdf

benshares

Thanks for all the insight - I'm going to stop by my local bike shop that services older beaters and see if they have an extra brake arm clip. I saw the no-rotation washer when I took the wheel off - does the "arm" of that washer just brace on the nut that holds the wheel on? i.e. does the rotation of the washer matter? I can see that the direction it faces is important, but can't tell about the orientation.

FBinNY 

No, the tab on the washer rides in the dropout slot, so the axle can't rotate.

Dan Burkhart 

You can have the anti rotation washer facing forward or rearward in the dropout. It makes no difference to the hub. What matters is that it allows you to properly tension the chain with the wheel aligned facing rearward, or that the tab engages the dropout if you have it facing forward.
So, if you have it facing rearward and it prevents you from taking the slack out of the chain, flip it around to face forward.

benshares

Thanks for the clarification - found this image with what looks like a pretty ideal installation and helped me understand

FBinNY 

Yes, that shows it, but not quite. Assuming there's room, as there is here, it's better to to have the key toward the closed end of the slot. That's to make it harder for any torque on the key to spread the dropout.

It's not critical, but still good practice.

Dan Burkhart 

Agree with FB, in this case, it looks like the washer should be facing rearward.
But there is other stuff going on in that photo that has me scratching my head a bit.
The attachment point of the reaction arm anchor for one, but the derailleur is a real puzzler.

FBinNY 

It looks like a 9x3 mixed (derailleur + IGH) setup cobbled together by a real shoemaker (Italian slang for poor mechanic).

Combining IGH hubs with derailleurs isn't rare, but IMO is less than ideal, since it combines the drawbacks of both systems.

As for the odd brake arm attachment, this might relate to what I described earlier in the thread about the relative positions of the axles flats and brake arm. This can be often managed by using the right keyed washer, but may require loosening the left cone and rotating the axle so it's flats orient correctly with respect to the brake arm (and using the right keyed washer).

This photo is very useful for showing what NOT to do, except that at least that id does correctly show the washer tab engaging the slot.

BTW - I'm still curious where the OP found a working farm "local" to Brooklyn. I did find a few "farms" on the internet, but they seemed to be either rooftop farms or small community gardens, or greengrocers and restaurants.