Cycling UK Forum

Looking for a maintenance free reliable commuter I had a nexus 8 and roller brake fitted to my Ridgeback hybrid back in March this year. The roller brake is rubbish but I was very pleased with the Nexus hub. A month ago after 1600 trouble free miles the chain broke and I took the opportunity to overhaul the drive chain; new 1/8th inch chain, 36t Surley stainless chainwheel, 18t sprocket and I treated myself to a Surley Singulator chain tensioner to replace the Shimano. Very disappointed to find the hub jumping in all gears!! Consulted Sheldon Brown, got the gear cable adjustment spot on but still not right; still jumping in lower gears especially under load. New gear cable (nicely greased) didn't help. Back to Sheldon and other websites decided to give the hub an oil bath. Not wishing to pay the £60+ per litre for the Shimano oil I used Automatic transmission fluid (£8 per litre at Halfords). And the result is a much quieter and smoother hub but still some jumping especially in low gears under load. It's just a momentary thing accompanied by a loud clunk/bang which is very annoying. Help! any suggestions?

My suspicion is that you have one of two faults;

1) the gear adjustment is still wrong somehow; a sticky cassette joint or something will do it; or...

2) you've 'done something' to the hub innards during your oil bath.


In the latter instance if you have a drag spring hub (with castellated roller clutch retainer) failure to refit the drag spring correctly will produce a drive fault in gears 2-4 and 6-8. But the #1 fault I have encountered is that a ball comes displaced from the ball-ring when the hub is reassembled. It is incredibly easy to do this, mainly because the design is a bit poor; a better design would go together more reliably.

What seems to happen is that a ball goes missing from the ball ring during reassembly. Most usually it gets as far as the nearest ratchet in the hub, which is right next to the ball-ring. Here, a ball will foul the primary gear train. This will generally produce a fault in either gears 1-4 or gears 5-8, and (in rare cases) both, depending on how the loose balls sit exactly.

The primary gear train in most 8s Nexuses (Nexii..?) has a clutch (C1) with four pawls which transmit the drive in gears 1-4 and are overrun in gears 5-8. These pawls engage two at a time; the other two do nothing. It is pot luck which pair engage. If one pawl engages and the other doesn't, the drive will slip. There are two springs (circular wire springs, looking like oversized snap rings) that both locate and spring the four pawls. Each spring springs two pawls and helps locate the other two. [Normally you can see one of the two springs in the gap between the driver and the R1 ring gear, right next to the ball ring, when the Centre is out of the hub.]

I have now seen several instances where a loose ball has fouled one of the pawls and deformed the nearest (visible) spring. This immediately results in foul noises and if the hub is ridden very far usually something breaks before too long.

To diagnose properly, remove the cassette joint, the sprocket, and the dust cover. Now look at the ball ring clip. Is it deformed? If so, don't panic, you can buy this part as a spare. Now look closer; are all the balls in the clip or are there any (even one) missing? If so, you need to pull the Centre, and find the missing ball. Often you will see the rogue ball sitting in one of the C1 pawl pockets.

Regardless of whether you can fish the ball out or not, you should really inspect the C1 clutch for damage. Only if there is clearly no deformation to the visible spring (and all four pawls are OK) could you take the risk and omit to do this; however normally you simply can't see well enough to be sure of this without further disassembly.

To inspect properly you need to remove the circlip on the left end of the Centre and remove the main planet gear assembly, which comes off in one big lump. [There are detailed instructions with photos on how to do this on the shimano.com website in the 'techtips' section, but it isn't too complicated]

I would suggest that you remove the C1 pawl springs one at a time (else all the pawls fall out) and check them (and the pawls) for damage. I'd suggest that you remove the pawls only one at a time too, so that you are sure they go back in the right place. Note that there are two types of C1 pawl and each similar pair must be installed 180 degrees apart, so that the nearest neighbours to each pawl are both of the alternative type. Deformed springs can normally be reset round, but broken pawls cannot be replaced; shimano don't sell these as spares... . In an emergency it is OK to run with two pawls set 180 degrees apart, but both springs must be fitted; whilst only one actually springs a pawl pair, the other helps retain them too.

When reassembling the hub I have found that the ball ring is at very much reduced risk of damage if the Centre is rightside down when it is put back in the hubshell; this is the exact reverse way to the 'obvious' way to do it (lowering the Centre into the wheel set rightside up), but rightside down, the balls in the ball ring are at markedly reduced risk of getting displaced into the wrong spot. If you have a bench vice, you can clamp the Centre (less the dustcap) in it, left side upwards, and lower the wheel over it. Better still lift the loose centre into the wheel from below (i,e, whilst rightside down); this way you can be better sure you have not displaced one of the four pawls (on those Nexus versions which have them) on the left end of the Centre.

Once the left cone is installed (and adjusted finger tight to start with) you can check that the hub turns freely and that all the balls in the ball ring are present and correct. Once you are sure of this you can replace the RH seal/cover, the sprocket, the cassette etc.

It seems very boring and unnecessary to remove all the external gubbins from the Centre, but IME it is the only way to be absolutely sure that all the balls are in the right place.

BTW, for a lubricant, ATF has the virtues that it is oily, readily available, and pretty cheap to buy. It is however, not an especially good lubricant for slowly moving, highly loaded gear trains. Better than that is gear oil, and probably better again is (the right kind of) semi-fluid grease.

If you want an idea of how much worse ATF is as a lubricant, consider this; if you buy the most expensive ATF you can buy, (which is fully synthetic stuff costing about ten times as much per litre) the best that can be said of this magical elixir is that its lubrication properties are as good as a standard hypoid gear oil. Standard ATF is quite a lot worse (as a lubricant) than gear oil.

hth

cheers

Brucey thanks for the suggestions. I am pretty confident it's not the cassette, I cleaned it all up and it moves very smoothly. Sounds like a Sunday afternoon job to investigate the missing ball(s). I'll let you know how I get on. At least all this rear wheel removal is good practise for when I get a puncture on a dark winter evening.....

Regards

another common fault is the use of a plastic rather than metal ferrule on the gear cable housing where it enters the cassette joint; this can make the gear cable work OK for a while, but then go draggy, often so that selection of lower gears is affected.

cheers

Ivor, from your description it seems that the only change you had made to the bike before the gears started skipping was the drive train, and not the internal hub, so I would also suggest checking that your new drive train has been installed correctly and that the chain isn't skipping on the rear sprocket or catching elsewhere. A stiff link in the chain, not enough chain wrapped around the rear sprocket, or not enough tension in the chain etc. can cause this. IIRC the Surley Singulator has to be correctly tensioned with the help of a 18mm cone spanner and it's easy to get it wrong if you don't. Also if you're using an 1/8th chain then you must reverse the chain guide plates on the Singulator else the wider chain might catch.

Sum wrote:Ivor, from your description it seems that the only change you had made to the bike before the gears started skipping was the drive train, and not the internal hub...

you are quite right; I may have been looking for a complicated cause when there is a much simpler one....

cheers

Sum wrote:Ivor, from your description it seems that the only change you had made to the bike before the gears started skipping was the drive train, and not the internal hub, so I would also suggest checking that your new drive train has been installed correctly and that the chain isn't skipping on the rear sprocket or catching elsewhere. A stiff link in the chain, not enough chain wrapped around the rear sprocket, or not enough tension in the chain etc. can cause this. IIRC the Surley Singulator has to be correctly tensioned with the help of a 18mm cone spanner and it's easy to get it wrong if you don't. Also if you're using an 1/8th chain then you must reverse the chain guide plates on the Singulator else the wider chain might catch.

Yes worth investigating. I stripped down the hub (again!) as per Brucey's suggestion and all balls present and correct. I wondering if I have enough chain wrap with the Singulator, I have it set for pushing the chain down ( no space for push up) giving about 7 teeth of 18 engaged with chain. It's definitely an under load thing. I'll try going back to the Shimano tensioner which is a double sprocket affair and will give greater wrap.

if you have any kind of spring-loaded tensioner, and you are running a newer chain on an older sprocket, jumping under load is likely.

What happens is that the chain rides up over the (slightly) hooked teeth on the sprocket instead of engaging and this then feels like a jump. It happens more easily under load.

Weirdly the same sprocket can run OK as an (un tensioned or rigidly tensioned) SS setup, or just be a little noisy for a while with a new chain.

SA/SRAM sprockets and 1/8" chain fit shimano IGHs and are cheaper and can wear much better than the 3/32" stuff that shimano supply. With careful shopping you can buy both chain and sprocket for as little as about £5. A new sprocket is an easy thing to try and costs peanuts.

Another outside possibility is that the driver splines are worn and you are running a dished 3/32" sprocket with offset drive lugs; this can also result in slippage between the driver and the sprocket. Again a 1/8" sprocket usually fixes things because it generally won't have offset drive lugs.

cheers

Ivorcadaver wrote:Yes worth investigating. I stripped down the hub (again!) as per Brucey's suggestion and all balls present and correct. I wondering if I have enough chain wrap with the Singulator, I have it set for pushing the chain down ( no space for push up) giving about 7 teeth of 18 engaged with chain. It's definitely an under load thing. I'll try going back to the Shimano tensioner which is a double sprocket affair and will give greater wrap.

It sounds like your chain meets the rear sprocket somewhere between the 7 and 8 o'clock position, which suggests that you may have about one link's worth of slack (i.e. the chain overlaps by about one inner link or one outer link when you try and join it without the tensioner). With a non-adjustable spring-loaded single-pully tensioner this amount of slack can result in the chain occasionally slipping on the rear sprocket, even if you have both a new chain and rear sprocket (or at least that's what I found when I converted my geared bike into a single-speed). You could try increasing the tension of the adjustable singulator but I think going back to the Shimano double-pulley tensioner would be a better test to see if the chain wrap or the Singulator was the issue. If the chain still jumps, and you're certain you don't have a stiff link somewhere in the chain, then it's back to examining the IGH as Brucey suggests.

It's going back a way now, but I did some trials with our greenpower team about 5 years ago to see if we got an efficiency improvement by oil lubricating the nexus8 & at the time I bunged ATF in because I had a bottle in my shed........ It's just possible that ATF has sort of become synonymous with this procedure because of that accident, because I was one of the early "tryers". Unlikely I guess. Anyway, points I was going to make - 1) the nexus drive side cover doesn't seal well, the oil may well leak - in the cars I had to bolt a clamp plate to the spoke flange to keep the oil in. 2) during reassembly there is one point where you have to line up some of the planet gears properly to avoid the sort of problem you describe - shimano even supply a special tool I think - are you happy you got this bit right?
FWIW in my opinion oil always does a better (lubricating) job than grease and does alter the feel of the transmission and give a much longer "spin down" time. Whether that actually equates to better efficiency in use - who knows
BTW I owned a bottle of ATF because it was specified by borgwarner (later tremec) for the T5 manual transmission I'd put in my V8 MX5 - so I reckon it can't be too bad and must count as an effective gear oil....

PS a little way down this page is a photo of my oiled nexus8 in greenpower car guise......
http://hubstripping.wordpress.com/nexus ... ment-88411

yes, the RH covers vary enormously; some have an additional seal component built in, but despite this none are actually guaranteed to seal perfectly.

Plenty of manual and auto gearboxes specify ATF rather than (say) gear oil. However in many cases the longevity of the gearbox is definitely improved if a more viscous oil is used. The reason they don't do this is usually because the shifts get baulky, especially when the 'box is cold. Special gear oils are made that lubricate better than ATF and still allow reasonable cold shifting but these lubes are eye-wateringly expensive.

Since bicycle hubs don't (as a rule) suffer from baulky shifting etc when they are lubricated with more viscous oil, ( it has to be easier to push the stuff around than the greases they use, surely...?) then there isn't the same argument for using a less viscous oil in a hub vs a car gearbox.

The greenpower experience is interesting, because the the conditions are a little different, even if the powers and torques are sometimes comparable, pedalling is a very pulsy torque (which can let oil back into contacts when the load is off) and the speeds are usually lower, too. If I were running a hub like that at high speed I'd probably try and use a thinner oil, too.

The lube I've developed for hub gears has better lubrication properties than any gear oil, has solid lubricants and anti-corrosion additives in it, and is highly thixotropic in nature; i.e. it thins out as soon as it is being sheared (like tomato ketchup). It is barely any more viscous than the base oil is when the hub is actually running, but is thick enough when stationary that it doesn't leak out when the bike is standing.

cheers

The oil sounds intriguing Brucey...
ooops - hijack warning......

Sidetrack to thread; the experience to date is that leakage rates with my lube -even with imperfect seals- are modest i.e. usually acceptable provided two things apply;

1) the lube is not being sheared violently immediately by the imperfection in the sealing, and/or

2) the speeds don't become very high on a large diameter hub.

In the latter case the shear forces get high enough that the lube goes into 'lots of ketchup out of the bottle at once' mode and out it comes if there is almost any leak path and the lube is of minimal viscosity.

The latter issue is probably solvable by making two different grades of lube; in a large diameter hub with imperfect sealing, you would likely have to use the slightly thicker grade.

On standard SA hubs and similar (i.e. without a RH cover), the shearing is strong enough in the ball-ring that some lubricant loss is inevitable, even with the standard grease. (This is partly why such hubs seem so prone to water damage in the RH ball-ring, I think, if not regularly lubricated). Unlike in SRAM and some other hubs, in traditional SA hubs the ball ring is placed at a smaller diameter so that not all the lube can be lost from the hub, just most of it. This allows the lube to be used in quantity if some leakage is acceptable ( or in conjunction with an improved seal if less leakage is desired). It also allows the hub to be run with a reduced quantity of lube in it instead; this way, the bearing still appears not to be so vulnerable to water damage as normal, unless it is stored unused, with a quantity of water inside, for prolonged periods. The reason for this is probably that the corrosion inhibitor is effective, but only gets to where it is needed in enough quantity if the hub is used from time to time.

cheers

Hi guys,
I'll be having another go at the hub this weekend (domestic duties permitting). Many thanks for all the suggestions. I'd just like to add my totally off the top the head views on lubrication. I think there is a world of difference between a bike hub and an automotive transmission. The forces involved are very different; if I'm feeling very fit on a good day I might achieve 150W, compared to 50kW from a car engine. Automotive transmissions operate hot (>100degC) for extended periods and tens of thousands of miles. I know a hub is tiny compared to a car gearbox but I wouldn't mind betting the torque is way lower in a bike hub. In the absence of anything else I have used olive oil and Vaseline on a chain and it worked fine. Probably any old oil of a reasonable viscosity would work in in a hub. I have no scientific basis for these views and would welcome some hard evidence.

Regards

torque is what kills transmissions, not power per se. Cyclists develop quite a lot of torque, even though the power isn't that high, and the gears etc are quite small. The tooth and pinion loadings in bicycle hubs are not a million miles away from those you get in other transmissions, but the speeds are much lower. Bearings invariably accept more load when rotating quickly than when they are rotating slowly, because a lubricant film is not so easily maintained at low speeds.

I'd argue that bicycle transmissions have a harder time of it than many other transmissions. Lubricating them with inferior lubricants will surely hasten their demise vs good quality lubes, but sadly bicycles generally get a choice between whatever happens to be lying around at the time and.... nothing....

Almost anything is better than nothing.

cheers