bammai123

Hello all, my bike suddenly broke and I really need some of your expert's advice. When I ride on my Dahon folding bike with Shimano Nexus 8 gear hub, I can turn the pedals and the chain and gears will move. However, the wheel doesn't move and the gear hub makes a loud clicking noise. However, if I don't sit on my bike, the wheels will turn fine. Does anyone know what is wrong? Thanks so much!

dabac

If you try to restrain the wheel while pedalling off the bike, what happens then?
Will it still (try to) turn?
If the hub engages as it should with the bike unloaded, but disengages when loaded, that would suggest that the shifting is going out of adjustment with weight on the bike.
Not that usual on Nexus hubs as they run full housing, but not impossible.
Do you know how to check shifting adjustment?
There is a yellow line on the collar at the hub that turns when you shift that should line up with another line on the fixed part of the hub when in 4/5th gear. There are manuals to be found online. You’ll have to look up the specifics.

Iride01 

Just to be certain, this is when you pedal forward?

If chain or cogs are very very worn, then one or both might need to be changed. Can you tell if the chain is skipping over the cog while you pedal with weight on the bike?

You'd likely have to have a lot of mileage on the order of 10,000 miles or 20,000 miles maybe more for it to wear that much to cause skipping.

Otherwise the issue is internal or maybe adjustment and I have no current experience with IGH hubs.

Dan Burkhart 

You make no mention of how old this bike is or what sort of usage it has seen, but among the possibilities is worn splines on the cog. There are 3 and over time, they can wear down and cause the symptoms you describe.

bammai123

Thanks for all the feedback. I actually got the bike used last year and supposely I was told that it was not used a lot. (I believe it as everything else on the bike look pretty decent.)
I tried to line up the yellow line and it didn't help.

youtube. com/watch?v=9BFzBBMW5tY

I took a video of the problem. Thanks!

Dan Burkhart 

And does it do this regardless of which gear is selected?
The first step in diagnosis would be to remove the wheel, then remove the cassette joint and sprocket from the hub. Then inspect the splines on the sprocket to see if they have been sheared off.
If that all looks good, then something is going on inside the hub, but I'm leaning towards what I first suggested if it does this in every gear.

Bill Kapaun

I would expect the "click" every 1/3 revolution of the cog.
One should be able to mark a tooth with white out/fingernail polish etc. and observe.
Else do the math-
Chain ring teeth/cog teeth*3 per crank revolution. Crank it a few times and count the clicks.
See if the actual number = the predicted number.

Dan Burkhart 

Yeah, from watching the video, I couldn't be sure, but it looked to be about 1/3 revolution between clicks.

Bill Kapaun

Assuming it is the cog, if the OP wants to change their gearing, now would be a good time.
Get a larger/smaller cog as desired.