Diagnosing hub wobble (Shimano Nexus)

Question

I have a Babboe City cargo bike with a Shimano Nexus 7 rear hub. Just coming into home on my last ride there was a bit of noise from the drivetrain and, on closer inspection, some other symptoms. The back wheel now has a wobble that is coming, as far as I can see, from somewhere inside the hub (i.e. this is not a broken spoke or similar issue, the hub wobbles along with the wheel). I tried taking a couple of videos, apologies for the shaky camera but I hope the issue is visible. I think it's probably clearer in the first link below. The wobble is present when turning the pedals backward, i.e. the drive is not engaged, and seems to be unchanged when I change gears.

Along with this, the pedals get 'pulled along' by the rear wheel (another video below). Holding the pedals in place will allow the read wheel to keep spinning without any horrible noise, but there is some rubbing noise coming from inside the hub (?) which causes the back wheel to come to a stop rather quickly. To my ear the noise sounds like bearings rubbing (?), but not crunching or grinding.

I'm trying to assess whether I'm looking at a repair, either to be done myself or by a shop, or looking into replacing the hub (or wheel). I'm reluctant to open it up without a plan, since from the diagrams I've seen it's not the simplest of mechanisms. In terms of overall maintenance skill level I'm reasonably experienced. I have an '80s era road bike that I maintain myself, and I either have or would be comfortable adjusting or replacing any part on that bike. However, I've never worked on an enclosed hub.

Answer 1

The hub likely needs normal maintenance. The kind of noise and drag you're getting is fairly normal when these need lubrication. Hopefully it hasn't gone so long it's been damaged. Play developing also implies needing overhaul.

Shimano 7 and 8 hubs come apart in layers. The first one is pulling the core of the hub from the shell, which allows you to tank it in an oil bath and grease the bearings as indicated in the product manuals available at si.shimano.com. This constitutes normal maintenance and needs to be done for the hub to last. It's not super technical, maybe approximately on the level of overhauling a cup and cone hub. In some regard it's easier because all the small stuff stays together as a unit.

The second layer is taking apart the hub core into what you could call its subassemblies. You can grease some things that would normally be oiled by doing this, and some are advocates of doing that for weatherization/local climate resistance purposes. The other reason to do it is to find and replace broken things that can't be seen or accessed otherwise. The second layer is more technical than the first. You mostly just need to go slow and keep things in order; it's not fidgety or difficult to figure out, and it only really goes together one way. Shimano does publish procedures for this.

I can't see the wobble you mention. If it's looseness coming from the hub bearings being loose, you'll be able to adjust that out at any time as a regular hub adjustment. If it's coming from elsewhere, that would imply something being broken as well as I can figure, and you might need second layer type service to figure out what and whether there's a replacement available.

The dealer manual files for your model will let you know what special tools are needed, cone wrench sizes etc. Substitutions for the proper Nexus/Alfine disassembly tools and how prudent it is to go there is a whole other conversation. Same with substitutions for the Shimano hub bath oil and Nexus grease. My station in life has me always and only using the Shimano products so I don't have a ton of opinions there. The oil is expensive and intended to last many, many hub dunks. Many on the internet report success using gear oil instead.