Sweep wrote: Is it fair to assume that a "slippage" soon after changing gear is far less serious than one some time after you have made the change - on the basis that this may just be a problem with initial engagement of the gear rather than an inability to stay in that gear? (If I get a slippage I always change to another gear immediately though this may not have always been the experience of the gearbox - the gf rode it once and despite being asked to tell me if she encountered slippage during a ride chose to tell me at the end).
if you pedal forwards (without significant force, for 1-2 full turns of the pedals) during the shift, the gear should go in properly. If you freewheel or backpedal, it won't, not always. In the latter case it may slip as it goes in, or not go in fully before you pedal hard again. Any slippage can cause further damage. (Re adjustment, see my note in the X-RD5(W) thread.)
However I have noted that on all NIG hubs it is possible to get a 'funny noise' even in the direct drive gear, even on hubs that are in super condition. This seems to happen maybe one time in twenty when shifting to the direct drive gear, normally about five pedal turns after making the shift. After much thought I now suppose that this is the result of just one of a pair of pawls failing to engage properly; either between the driver and the gear ring, or between the gear ring and the hubshell. One pawl can engage if the parts are not centred properly; given that the driver is always able to rock slightly and that the gear ring has a radial tolerance I guess this is going to happen from time to time. Normally a brief backpedal or freewheel allows the pawls to engage properly and then normal service is resumed. So for that reason I'd suggest that on hubs that are prone to this (it varies) pedalling with little force for a few turns after a shift into the direct drive gear (or whichever other gear does similar) isn't a badi idea. If the sole engaged pawl squirms badly (it will) and then slips out (again it will) and this happens under full load, this is exactly the kind of thing that will damage a hub.
Another question. I have noticed that SOMETIMES when wheeling the bike backwards (as you might briefly when manoeuvring it when walking with it) I get a clicking from the gearbox and even a resistance to this backwards movement. Is this a sign of anything?
The NIG design of hub (in high gears) will actually break into myriad tiny pieces if you wheel the bike backwards and the actuator plate doesn't do its job and/or the main clutch isn't lifted on its ramps. This is because the driver is in mesh with both the gear ring (via the pawls) and the planet cage (via the main clutch). The splines between the driver and the main clutch are angled (presumably so that the clutch is forced into engagement) but this (or simple friction in the splines) means that the angled ramps on the reverse face of the driver cannot force the clutch off reliably when the bike is wheeled backwards. This is when the actuator plate is meant to defeat the driver pawls, so that the hub doesn't load itself (effectively by selecting two gears at once) and then shatter. If the actuator plate is faulty or worn then it won't do its job and the hub will break. In theory the wearing parts of the actuator plate fall into two categories; those that see wear all the time ( like the locating tabs, the eventual failure of which causes the actuator plate to come adrift catastrophically) and those that see wear only when the bike is backpedalled (low loads) or wheeled backwards in high gear (high loads).
My advice is not to wheel the bike backwards in high gear, and in the long run avoiding backpedalling (esp in high gear) isn't a bad idea either. If there is appreciable resistance already when wheeling the bike backwards, this most likely is an indication that the actuator plate is struggling to do its job. If I see this I will recommend that the actuator plate is changed without delay. It is a cheap part and can be fitted without a full hub stripdown; the driver assy will come out quite easily once the RH cone is unscrewed. However it isn't a bad idea to check everything else at the same time, so pulling the whole centre is best.