mc510

After looking over so many threads about Nexus 7/8 hubs slipping/skipping gears, I still don't really have a good sense of what's going on with mine or if it can be improved! I've got a Breezer Downtown with Nexus 8 hub and matching twist shifter, got about 500 miles on it. At about 100 or 200 miles, I noticed it slipping but only in 5th gear, and it's only been getting worse since then. It's not skipping to another gear, just popping out of gear entirely for 1/4 rotation then catching again. Happens even when I'm applying only moderate pressure, and sometimes it happens every couple of minutes that I'm in 5th. No odd bends in the cable; yellow adjustment marks are perfectly aligned (when in 4th). At about 300 miles I gave the hub a dip in 90 weight gear oil. Is there something about the design of this hub that would cause this problem to happen only in 5th? Any fixes to try? And is the hub mechanism at risk of becoming more damaged over time from all of this hard slipping?

mc510

From an old thread, and Does this mean that in 5th, with no pawls involved, the roller clutches have to hold more force than in other gears? I wonder if my gear oil is too viscous, or if it has washed away the grease that I put on the outer bearing rings, thereby becoming even more viscous, and messing up the roller clutch operation?

dsbrantjr

What lubricant does the manufacturer recommend?

FiftySix

I have a Nexus 8 in my 2013 Norco that I bought several months ago. I normally ride it in 6th gear, but drop to 5th to start out at some standing starts.

I did do a hub service back in April this year with materials I already had in my garage. I flushed the hub with ATF, let that drain, greased the bearings with automotive bearing grease, and filled the hub repeatedly with 85W140 gear oil. You can read some of my trials and tribulations here. https://www.bikeforums.net/bicycle-m...e-arrrrgh.html

In my case, my Nexus 8 works the same as before. Which means if I don't do a few degrees of backpedal during a rolling shift, the hub may make popping noises as if a pawl is skipping. It will also make very slight whirring noises which I can make go away by another slight backpedal to "find another spot" in the bearing clutch engagement (I'm guessing here).

So far, 5th gear works fine in my hub. Even if I stand up to pedal to from a standing start, which I don't think we're supposed to do with Nexus 8s.

Dan Burkhart 

No. In 1st and 5th, it is the outer roller clutch on the left side that drives the hub. This is because none of the sun gears in the planetary carrier are engaged, so no power is transmitted to the high speed roller clutch.
Whenever any of the three sun gears are engaged, power is transmitted to the high speed roller clutch, and the direct drive clutch is simply over run.

mc510

Got it. Well, not really, but at least I get that it's not the case that 5th gear places unusual force on roller clutches. Is there anything special about 5th gear that might explain why on this gear is slipping, and might point me towards a fix?

Dan Burkhart 

Between 4th and 5th gear the clutch transitions from being disengaged from the planet carrier, to engaged which bypasses the low range reduction unit. At the 9:40 point in the attached video is an explanation and demonstration of how the clutch engages.
If the shifter adjustment is off even slightly, the clutch could get hung up on the ramps preventing full engagement.Once the shifter is moved to the 6th gear position, the clutch tabs are well clear of the ramps permitting full engagement.

BookFinder 

Interesting reading, this. And perhaps fortuitous for me.

The only reason I've not pulled the trigger on a Motobecane Elite with the Nexus hub is that I've been so busy lately with work that being settled for a delivery is a problem.

How commonplace is the type of issue that I'm reading about in this discussion?

FiftySix

Your videos explain so much, Dan. Thank you for taking the time to make them and post them on the net.

mc510

Good question; I don't know how common this issue is, or the (related?) issue of dropping down a gear. But I do know that 100% of Nexus hubs have a great deal of internal friction that somehow just didn't register to me before I bought mine. I imagined that a Nexus 8 would be like my old SA AW-3 (bulletproof, low friction) but with eight gears. In fact, it's neither bulletproof nor low friction.

mc510

Okay, based on this, the only thing that I can think of trying would be to lubricate the shifter cable, and then try moving the shifter adjustment a hair off center (i.e., so the yellow marks do not perfectly line up).

Dan Burkhart 

I would not advise mis-adjusting the alignment marks in an attempt to get the clutch to engage, because it could cause worse problems. The adjustment is most critical to ensure the pawls that couple the sun gears to the axle are fully extended in each gear position.
If the problem persists, an oil bath lube job may help.

mc510

Well, shoot; I guess there's very little that I can do to try to solve this. I will definitely give it another oil bath and keep my fingers crossed, but I'm feeling like I'm probably going to end up replacing this bike a lot earlier than I had anticipated

Thank you for the sage advice, Dan; I really appreciate all the effort that you put into helping cyclists understand and fix their bikes.

Dan Burkhart 

Oh I missed the part about how you have already done an oil bath. I have had success treating engagement issues in different hubs this way, and function has always improved in any hub I have given the oil bath treatment.

mc510

Quick update. I pulled the guts out, found that the oil had mixed with the grease (that I had applied on the ball bearings) and created a uniform sludge over everything. After cleaning and relubing (90 weight gear oil bath, grease on bearings), it's now back together and no longer slipping in 5th , so I'm going to put the whole problem down to improper lubrication that was apparently preventing the clutches from properly engaging. I didn't think of it until after reassembling, but next time I'm going to not put grease on the large bearing race, since that one should get sufficiently lubricated by oil. And if I still find that the grease is getting washed off the small bearing race, I'll conclude that that one also is sufficiently lubricated by oil and I'll leave the grease off that one as well.

BookFinder 

Thanks for the update. I’m still reading up on the hubs.

sweeks

Not sure if this is helpful, but I've got about 10,000 miles on a red-band Nexus 8 hub that gets a yearly dip in gear oil and the bearings (including the big one on the drive side) are greased with "Nexus" grease. No slipping.
Skipping the grease probably will be OK if the oil dip is done with some frequency, but I'd recommend being careful if the bike is ridden in wet weather. The only water-related problems I've had were on a Nexus 7 speed hub which had water incursion on the drive side, resulting in some (fortunately) superficial rusting of the race. I think grease provides better protection against water than the oil does.

Joe Bikerider

I’ve got two bikes with Shimano 8 speed hubs. Both have different part numbers marked on the outside of the hub. The Shimano repair manual specs different lubricants for each.

SG-8R31 on my Biria needs special grease. No dipping in oil.
SG-C6001-8R on my Linus specs dipping in LU8408 WB lubricant.

The 8R31 hub is on it’s 5th year of almost daily riding. I’ve lubed it once, due for a second. No problems. The C6001-8R hub has not been serviced yet. I intend to use the Shimano lube to avoid problems that have been described. Products are available from Universal Cycles.

Fiddling with the adjustments is a good way to frustrate yourself as you make things worse. I know. Set it properly and ride.

everytime this topic comes up it starts off negative. Like this one did. I don’t understand it. My experience is adjust it properly, use the right lube and follow the procedures and these hubs will ride beautifully for a long time. Thanks.

sweeks

My first Nexus-8 had the black "Nexus grease" (same as on two Nexus-7 hubs) when I first opened it, so I was surprised when I opened the newer ("red-band") Nexus-8 and found it covered in a white lithium-type grease. I've been dipping both hubs annually in a synthetic gear oil and greasing the bearings with the Nexus grease. The hubs have been working fine for at least 10 years. The gear oil is Royal Purple 75W-140, which I've been using in my Alfine-11 for the last 7,000 miles.

mc510

Do you find that the official Nexus grease gets washed away by the oil, or does it resist that and stay on the bearings?

sweeks

There's not a lot of oil running around in the hub, since the hub gears are allowed to drain for a few minutes after dipping. The gear oil (75W-140) has some viscosity and coats the gears pretty well. Still, after a year some of the grease does get mingled with the gear oil. This doesn't hurt the gears, and the bearing races remain un-worn except for a polished ring where the balls contact them.
As far as I can tell, the "Nexus grease" (the black kind) is some kind of moly lube. I wouldn't hesitate to use a good wheel bearing grease (maybe "marine grade") if I didn't have the "official" stuff.