Greasing a Nexus

Niholas usually have hub gears, and these days those are usually Shimano Nexus 8 after the unfortunate demise of SRAM's P5 and S7 on the market.  These need grease once in a while.  For me, that means whenever they have a hard time holding one or more gears, or otherwise seem too crappy.  (Fun thought on crappiness: at least in hilly Oslo conditions, switching between Nexus 7 & 8 and SRAM S7 is a process of relief from the irritations of whatever hub you were riding, followed by growing irritation at the issues of the one you are now riding.)

So for a while after moving to Oslo I took my hubs down to Copenhagen for greasing, which came to an abrupt end after one visit to a well-established chain-store shop in Birkerød (north of Copenhagen).  I brought them two wheels without the bikes, one a Nexus 8 and the other a Nexus 7, and got back to two nicely cleaned hubs a couple days later.  All was well until I arrived home in Oslo and put the Nexus 7 to use as winter began.  Soon it was leaking, and smelled fruity.  Actually the smell was exactly like a "Muc Off" chain lubricant which has the distinction of not only smelling fruity, but being somewhat pink in color, achieving who knows what.  (The leakage wasn't pink of course, it was filthy, but I am really suspicious about the origin of the lubricant they used at the shop.)  So it leaked and stank, and eventually seemed rougher, and if I recall correctly was not as secure about holding a gear.  To cut the story short, the Nexus 8 had the same issue.

Screw the so-called professionals, it was time to fix this myself (the internet explains how).  I don't intend to write a hugely detailed rundown of how to take apart a hub, but basically you take the hub apart on the drive side until the sprocket is removed, then flip it over and use two thin wrenches (cone wrenches) to remove two nuts from the axle, then lift off the non-drive-side end of things and drop out the internals via the drive side.  I like to put the axle nut on the non-drive side to make it nicer to hold, and I made a handy hub-holder by drilling a hole in a board.  High tech stuff here.

tools of a nonprofessional hub greaser

10 year old Nexus 7 (SG-7C18)
after a dip

Nexus 8 (SG-8C31) dripping out
some pink stink after two
dip & grease rounds

I clean the hub shell out thoroughly via baby wipe and toilet paper, and also remove some grease-mess from the surface hub internals, but not so much.  I have not thus far attempted any disassembly of the hub internals, although I think the Nexus 8 might benefit from getting grease into gears that are not otherwise exposed (thats on the to-do list).  Hubs with coaster ("foot") brakes (as mine have) can have the brake pads jump off and they need to be set back correctly.  The brake pads on Nexus 7 have a spring which pulls them a little closed, so they need to be pried open a bit to sit on the hub.  You'll figure it out.  Kind of like Legos, with grease.

Shimano recommends a dipping kit, so I found one online, plus their official hub grease.  I dip the hub for "a while" and then remove it so it can drip for "a bit" before I put grease all over interesting places.  One thing I wondered in the years before I attempted this was how to grease the coaster brake components.  My answer: a whole ton of grease, just go nuts at that end of the hub.  Often I have extra grease pressing itself out the non-drive-side the first ride, but I don't much care.  Dry brake pads are lame, and there are hills here in Oslo.  I have read that some people may want different grease for the braking surfaces, so far I have not been sufficiently professional (or wise) to do anything like that.

So I have now done this procedure on a Nexus 3 & 8, plus at least three Nexus 7's, and of these hubs I've opened several more than once.  (Score keeping: I have 5 Nexus 7 hubs, also a rare Nexus 5 SG-5R30.)  But about opening some more than once.  You see, there is a drawback to doing this yourself.  Shimano likes cup & cone bearings, and those need to be tightened correctly, or else.

Nexus 7 (SG-7C30) with sad bearings

Nexus 8 (SG-8C31) with sad bearings

Now, I have read a bit about how to tighten cup & cone bearings and honestly what I read was not super helpful in this context, which is a gear hub with a coaster brake and bolt axles.  My current procedure is to get the wheel set in the frame, pull it back so the chain is sufficiently tight, and then tighten down the drive-side bolt in a serious way.  The frame should either be upside-down or hanging on something; the rear wheel needs to spin freely.  Then I loosely attach the brake arm and non-drive-side axle bolt, but do not tighten it so much that any pressure is applied to the nuts that adjust the bearings.  Then I turn the first (the larger) of the two tightening (cone adjustment) nuts until the wheel shows signs of increasing resistance when spun.  At some point I decide that it seems tight enough, then I tighten the second (smaller) nut good and tight (while holding the larger in place) and properly tighten the axle nut.  Now the wheel is probably tighter than it was before the axle nut was tightened.  If its too tight, rewind a bit, loosen things, tighten things again.  Spin the wheel a lot and go by feel.  If it spins really easily, thats probably bad.  Next time I go by a Danish bike shop, I should remember to spin some back wheels and get a feel for factory-fresh resistance.

My first bearing tightening issue was a bearing retainer failure (non-drive side) during or shortly after a big downhill on a hot-for-Oslo June afternoon, apparently braking was the final stress that tipped things over.  Once I reached the flat at the bottom of the hill, it was a fairly short distance before the wheel started crunching.  The bearings had lasted about 6 weeks after I had greased the hub.  I was surprised by this, because it wasn't the first Nexus 7 that I had greased up (the first one was the hub contaminated in Denmark).  I greased the first hub on the 1st of Feb 2018, and has done fine since.  I concluded that the cone adjustment nuts had probably loosened on this 2nd Nexus 7.  I grabbed the bearings and retainer from a different wheel, put things together again, and its been fine since.

I also greased the Nexus 8 that was Muc Off'ed in Denmark.  I was very pleased how the wheel spun so easily and had no observable looseness (as in, I observed no play).  Seemed good.  I guess I rode a couple hundred km's before I decided to do an uphill stretch standing on the pedals in 5th (direct drive).  As before, the bearing retainer (also non-drive side) broke into bits and this time the wheel was partly jammed, couldn't even roll the bike all the way home.  With this failure, it seemed clear the cone adjustment nuts where not loosened, apparently they were just not set tight enough.  So I fixed that also by replacing the bearings and retainer, but it wasn't so long ago that I can say how it will last.  (Side note: the bearings and retainer for Nexus 7 and 8 are interchangeable, at least for the hubs I have, and spares are possible to order.)  This second failure was the point that I adopted the procedure outlined a couple paragraphs above.

Anyway moving on to farther in the past, in 2017 we had bought a gear-hub bike for our son down in Denmark and almost immediately it went out into the forest and got a bit wet.  Apparently more wet than we realized.  We left it in Denmark until the next summer, and when we returned I noticed some roughness while spinning the rear wheel.  Upon returning to Oslo with the bike, I took the hub apart and was met by rust, as shown.

rust in the drive side bearings
of a Nexus 7 (SG-C3000-7C)

rust on the guts

rust in the shell

In light of the amount of time that bikes with these gear hubs are ridden or parked in the rain, I'm pretty amazed that this hub had sufficient water ingress to rust.  We did get it discounted from a bike shop, maybe it had more of a history than we realized, or perhaps these hubs are particularly vulnerable to water found in forest settings.  Or perhaps my son submerged it.  Anyway it works pretty fine except when coasting, then it rumbles.

A bit of a shame that the newest Nexus 7 in the fleet was damaged so soon after purchase, but I'll see about getting some years out of it anyway.  As much as I love to hate these things, they last forever.