Nexus 8 still slipping

[vandjq]

There may be a co-operative cycle workshop near you, they may be able to help.

Brucey - there isn't anywhere like that in the North East. Hub gears are rare because it is so hilly. However, I think I have diagnosed the problem. I followed your advice and removed everything from the drive side of the wheel. Then I refitted the cassette joint. As I turned it against the force of the spring I heard a click about halfway round. When I released the spring, every now and then it stuck completely at the same point where it clicked. I then took off the cassette joint and found that I could freely move the cog the joint sits on. My conclusion is that the return spring is being obstructed. Even when it does not stick completely it feels very rough, which would stop the cable from moving smoothly.

If my diagnosis is correct, what is the cure?

[Brucey]

I think what is happening is that the sliding clutch isn't moving freely. This can cause the shift mechanism to bind on the 5-4 shift, and until it unsticks itself further downshifts (towards gear 1) just result in a slack cable. Actually riding the bike (on a bumpy road) often makes a hub work OK whereas it won't work consistently on a workstand.

I have experienced the same problem in N7 and N8 hubs (they both have a sliding clutch that is actuated the same way) and one of the things that makes a difference is the dragginess of the cable and exactly how the adjustment is set; basically on the 5-4 shift the mechanism jams less easily if it 'takes a run-up', i.e. if the mechanism is moving briskly as it hits the base of the shift ramp, it is less likely to jam. A slightly draggy cable can contribute to this problem. Hubs also 'run in' so that the ramp becomes smoother with further use. Trigger shifters are better than twist shifters in this respect too; they tend to release more abruptly.

A slightly freer-er running cable and actually riding the bike might make it work OK...?

cheers

[vandjq]

Brucey - I see your point about the shift ramp being a bit steep and needing to be worn down by use. But I'm not impressed with Shimano's quality control in shipping new hubs with a built-in fault. It reminds me of British Leyland.

Is the sliding clutch under constant pressure from the spring, or does the pressure ease off to help the clutch move up the ramp?

I have fitted a brand new well-lubricated cable which appears to be working fine in both directions when disconnected from the cassette joint and pulled tight by hand. I don't think it is draggy.

I can't line up the yellow marks when moving down from 5-4 in the workshop. So I am concerned that I will do some damage to other parts if I use the bike. But I guess I will have to take that risk in order to wear down the shift ramp, and as you say the fault may not occur on our (very) bumpy roads.

Is it worth fitting a trigger shifter? The thing I like about the twist grip is the ability to shift down in one movement when stationery.

Once again, I am very grateful for your patience in helping me to deal with this problem.

[Brucey]

in fairness a lot of things can add together to create the fault where the selector binds part-way through its stroke, eg;

- stickiness in the cable
- bad adjustment
- sticky/misassembled cassette joint
-roughness on the ramps inside the hub (newness, wear or corrosion can cause it)
- axle being strained (bent or flexed) when installed in the frame

To examine the last of these, try undoing the track nuts with the gear selector 'stopped'. If the selector mysteriously releases or won't bind with the track nuts loose, you have your answer. If you can't get the gear selector 'stopped' with the wheel in the frame and the cassette joint off, you need to look at the other things.

To test the hub on the bench/workstand, it isn't a bad idea to use a short/straight cable specifically for test purposes. It doesn't take much in the way of bad ferrules and/or dragginess in the cable (wrong lube, bad routing etc) to send things out of kilter. As I mentioned before if you can't get it to work with all new parts, you are probably doing something wrong, and some hands-on help/guidance is called for.

cheers

[vandjq]

Brucey - I'm not sure if I made it clear in my earlier post that I actually removed the cap nuts and non-turn washers, removed the wheel from the bike, removed the cassette joint, dust cap, snap ring and sprocket, refitted the cassette joint only and actuated it by hand. When it stuck I removed the cassette joint and was able to move the sliding clutch with my fingers. So the fault must be in the hub, presumably with the ramp as you stated earlier.

[Brucey]

sorry I misunderstood what you meant. If you move the gear selector ACW (as if you were selecting gear 5 or gear 6) and then release it, it should have 'taken a run-up' at the ramp and should shift normally. Bad adjustment and/or a draggy cable can help to cause the selector to stick part way between gear 5 and gear 4.

When hubs are new it isn't unusual to be able to make them stick in that position if you put your mind to it; the 'run up' is quite important.

cheers

[vandjq]

'Sorry to revive an old thread, but it is basically the same issue and needs to be viewed in context. During the current lockdown I am hoping that people will have more time and patience to read this.

After my last post in Nov 2018 I decided to risk commuting with my new Nexus 8 hub and it ran well on a level flat tarmac route, about 5 miles each way, until I retired in May 2019. Since then the bike has been sitting in my shed and I have been using my other (derailleur) bike to go out for pleasure/fitness rides. The other day I decided to take the IGH bike for a spin as I was curious to see how it performed on hills. It ran nicely for about 15 miles, then suddenly the hub started to slip, to the extent that I was unable to select gears 1-4. I limped home using gears 5-8. Strangely, about half a mile from home on level ground the hub appeared to correct itself and I was able to use gears 1-4 again.

The following day I went out again on the same route, after making sure the yellow marks were lined up in both directions. The first 15 miles were a gentle climb, followed by level riding. Then I went down a long straight sloping street and shifted up to gear 8. At the bottom of the street I used the twist grip to go down through 5 gears at once, ready for a short climb before descending again. At this point gears 1-4 were once again not working, slipping all over the place. This time they did not put themselves right when I was close to home.

It appears that the hub is able to cope with very gentle riding on level ground, where the gear changes are few, as in my commute. I can ride it round the block from my house in gears 1-4.

I have had considerable discussion with Brucey about this issue, and he pointed out that there is a 'ramp' inside the hub where the clutch moves back from gear 5 to 4. The action of the clutch on this ramp is shown from 9:40 mins in this video:

https://www.youtube.com/watch?v=_Q5iEywX3yM

Once again I removed the wheel from the bike and then removed everything from the drive side of the hub, then re-fitted the cassette joint and turned it by hand. Once again, it operated most of the time, although it sounded a bit rough and I could hear it click, presumably at the point where it climbs the ramp from gear 5 to 4. But occasionally it 'stuck' in one position and there was no resistance from the spring.

By removing the hub from the bike and disconnecting the cable I have isolated the problem as being within the hub and not caused by bad adjustment or a draggy cable. There is no shop in the North East which is capable of doing any remedial work on an IGH. So I am stuck with a fairly expensive bike which I would not get much for on Ebay as it is faulty. As I have nothing to lose I am considering fixing it myself and would appreciate any advice on how to do it and where to source spare parts.

[Brucey]

even with a brand new internal, if you turn the gear control pulley slowly enough, you can often make the shift mechanism stall on the 5-4 ramp. Even slightly bad adjustment of the gear settings, a slightly draggy cable, a dirty cassette joint, and/or a slightly distorted axle can all add to the chances of this happening on the road. The fact that the hub works normally or not (leaving gears 1-4 unusable and the gear cable slack) says to me that the shift mechanism is probably failing to move normally, but the conclusion that there is definitely something wrong inside the hub is not sound.

However there is a whole list of other possible problems which may be causing/contributing to the fault including

- dried grease inside the hub
- faulty roller clutch on the first stage (two speed) gear
- shifting technique.

Re shifting technique; the hub is designed so that forwards pedalling (without normal pressure on the pedals) forces the shift control mechanism to move inside the hub, whereas freewheeling or backpedalling during the shift does not.

Re lubrication inside the hub; the factory grease is not good enough by itself. Shimano recommend an oil service on the internal at regular intervals. Missing that and leaving the bike standing in a shed is exactly the sort of thing that is likely to cause the hub internals to gum up and stop working reliably.

I can only repeat my previous advice which is to find a bike shop which knows about these gears; they may spot a problem which you have missed. The only other choices are to scrap it or to dig in and sort it out yourself.

cheers

[vandjq]

Brucey - This is my post from April 2018:

' I followed everyone's advice and replaced the Revoshifter, cable, housing, waterproof boot and cassette joint (CJ-8S40). The cable, housing and boot came with the new Revoshifter from SJS cycles (very reasonably priced). It had the requisite metal ferrule pre-fitted. I lubricated the cable with Teflon grease and cycle oil. I also fitted the cable to the outside of the frame, so there are no internal runs and there is continuous lubrication (in theory). I carefully filed the end of the housing at the shifter end and crimped a metal ferrule on. When I moved the yellow mark from 1 to 4 it lined up perfectly, and also from 5 to 4. This morning I did my usual 5-mile commute to work. My first impression was that gear changes were smooth and easy. But after one mile there was a very slight slip in 4th. Then after 4 miles there was a significant slip, one of the worst I've experienced.'

In July 2018 I claimed on the Shimano warranty and received new hub internals (I hope). The frame was damaged by slippage of the non-turn washers (the shop did not tighten up the nuts). So I claimed for a new frame under the Cube warranty, which I received in October after 5 months. I fitted new non-turn washers and tightened the (new) axle nuts to 35 foot-pounds. There is no damage to the frame drop-outs.

I have fitted a brand new, well-lubricated cable (the 4th one) which appears to be working fine in both directions when disconnected from the cassette joint and pulled tight by hand. I don't think it is draggy.

I bought this bike in June 2016 and am still having problems with it nearly four years later. As I said earlier, there are no shops in the North East which repair IGH, and if there were I can't see how they could do anything different from what I've done with cables, cassette joints etc.

Two ideas to save the bike:

1) I have often read about people converting derailleur bikes to IGH; is it possible to do it the other way round?

2) Cube do a derailleur bike which has the same frame as mine:

https://www.cube.eu/media_ftp/BIKE_Bild ... _light.jpg

Is it feasible to buy the frame only and add all the bits from the old one plus a new drive train? Or even get the LBS to do it, which is a Cube dealer.

Once again, I am very grateful for your patience and expertise.

[Brucey]

forgive me if I'm pointing out the obvious here but much of that work was two years ago now.

Under normal circumstances the replacement hub internal would be (at least) due a second oil bath service whereas I would suppose it hasn't even had one yet. Likewise the cables, shifter, and/or cassette joint could have started to gum up, so very careful examination and testing is necessary if you are to be sure of them.

Also, there is another possibility which I don't believe has been examined as yet. That is the possibility that the slippage is being caused by a worn sprocket, the wear being between the sprocket and the driver. This possibility didn't fit perfectly with the reported symptoms previously but it does fit rather better now. My guess is that the sprocket is a 3/32" one; these can wear so that they slip round on the driver splines, but only when there is high torque on the sprocket. This tends to happen in the lower gears rather than the higher ones.

When this happens you can usually see marking (rather than gross wear) on the end of driver splines and more obvious wear on the sprocket itself, on the three drive lugs. Such slippage and wear only occur when a 3/32" sprocket is fitted one way round rather than the other, because the drive lugs are offset to one side of the sprocket. However with a dished sprocket it can only be fitted one way round (sod's law says it'll be the wrong way of course) so you don't have a choice if you want the chainline to be correct.

If this is the problem or you are in any doubt about it then I would recommend that you buy a 1/8" sprocket and chain. A 1/8" sprocket cannot so easily slip in the same way because it is always well engaged with the driver, regardless of the way the sprocket dish is set.

If your sprocket is a 3/32" one, and you can manage photos of it (both sides, when it is off the hub), please post them.

cheers

[vandjq]

Brucey - I didn't start using the bike again until Nov 2018, after the new hub innards and frame were fitted. Prior to that the bike was in the dealer workshop for 8 of the previous 12 months. So I only used what was effectively a new bike for 6 months before retiring. Surely the original grease should have protected it for that short period?

Following your advice I installed a Sturmey Archer dished 20t 1/8" sprocket to improve the chainline, and a KMC B1 1/8" chain. They have also only had 6 months use, which I estimate to be about 1300 miles at most. I measured the chain recently and it has less than 0.75mm wear.

When I actuated the mechanism by hand yesterday all the components appeared to be clean and free from rust or dirt.

I don't commute any more so don't really need an IGH bike. But I was hoping to sell it for a few hundred pounds on Ebay, which is not possible if it is faulty.

Anyway, thanks for all your help.

[Brucey]

nothing stops the grease from drying out; just time does that, and should the storage be somewhere warm that just speeds everything up. Less use is possibly worse than more use; there isn't much mixing of the grease in use, but there is some rather than none. Shimano recommend an oil service at regular intervals. I recommend running their hubs in a good semi-fluid grease (following an oil flush) rather than their lubricant.

I have seen very many of these hubs fail and poor lubrication of the internal is a very common feature. Once the grease is a bit dry it just gets pushed away from where it is needed, and it tends to stay wherever it ends up. This leaves the hub badly lubricated where it matters most and whatever grease remains (where it might do some good) then tends to dry out even faster. If the sheer lack of lubricant doesn't kill the hub then the slightest damp inside the hub causes severe rusting in the loaded parts eg planet gear bearings (see the 'smoking gun' thread) and roller clutches etc.

Shimano's oil dip causes the dried grease to become soft again but if the grease was too dry to start with the grease has already been pushed into the wrong places and whether it is now soft or not is almost irrelevant; the best it can do is to separate again, and with any luck whatever oil dribbles out of it might do some good somewhere.

It is not guaranteed that your hub internal is dried out but it might have been well on the way before it was installed (I would expect a replacement internal to perhaps be worse than a new hub in this respect BTW); it certainly won't have improved itself since then, either.

cheers

[vandjq]

This should now be called 'Nexus 8 no longer slipping' . As I had nothing to lose I thought I would dismantle the internal assembly and see if I could find any obvious faults. But before doing so I read every post in the thread 'IGH lubrication: a smoking gun.' Then following Brucey's instructions I injected 50ml of gear oil into the non-drive side, most of which came straight out the other side. After cleaning the cassette with methylated spirits I re-assembled the bike. I left it overnight but there was no further leakage when the bike was upright. To my surprise I was able to line up the yellow marks perfectly in both directions, from gear 1-4 and gear 5-4. I then went for an 18-mile ride which included a 10-mile climb and the gears did not slip at all. This has hardly ever happened in the four years I have owned this bike.

I know Brucey advises using hypoid gear oil to initially lubricate this hub followed by SFG in the long term. But I didn't have any to hand so I used fully synthetic ATF instead, which is very thin. I can remember in my youth using hypoid to top up car gearboxes and I think it was thicker than ATF. Should I put more ATF in or replace it with hypoid when I can get some?

Now it does not look as if I need to dismantle the internals, and Brucey warns that there is some element of risk in removing them from the hub. The fact that that there was no slipping indicates that there does not appear to be any serious wear inside the hub, so is it reasonable to simply inject Land Rover SFG into the non-drive side? Or would it be better to take the internals out before greasing?

Lubrication (or lack of it) certainly is a smoking gun.

[Brucey]

the hub will probably work fine with the ATF in it for a fair while. Gear oil and/or SFG is better, but the main difference is that you will probably need to add more oil sooner than more SFG. If you have washed the original grease away, there is no oil reservoir in the hub, so (depending on how well the hub retains the oil) potentially more oil will be required sooner rather than later.

cheers

[vandjq]

Brucey - I've ordered some of that Land Rover swivel grease. Two questions:

a) Should I wait for a while before adding it while the ATF does its work?

b) Will it be OK to just add it to the hub without removing the innards?