Brompton chain issue.

[Paulus]

Just changed the chain on my 6 speed Brompton, used an 8 speed chain, the chain jumps violently off when I change the gear to 3 on the internal hub, but only if I stop pedalling, if the cranks are moving the chain runs fine, it runs normally in 1 and 2 setting, any suggestions why this is happening?

Was the chain jumping before you changed the chain for the new one, is that why you changed the chain?

 

[Willam]

The chain might be rubbing the spokes because your derailleur's limit screw needs adjusting. Or, a chain link is stiff.

but you got me thinking…the 2nd gear in the hub is actually direct drive, whereby the 3rd gear is classed as overdrive and this is when the issue happens when the hub does its thing so looks like it could be a hub issue or more likely I need to remove the hub chain screw then refit, that might fix the issue…Ive removed this a few times as it needs removing when removing the rear wheel, never had an issue previously, but maybe this time it was an issue?

 

[Willam]

Was the chain jumping before you changed the chain for the new one, is that why you changed the chain?

No previous jumping, the chain was just in need of replacing, rusty and starting to stiffen up, oil wasn’t doing it.

 

[gizmo1994]

Sometimes the hub can cause excessive drag particularly when freewheeling. I have have sometimes found this, particularly when in the 3rd hub gear. The top of the chain will drop onto the chain stay as you coast downhill. I'm not sure if that is similar to the symptoms you are having. Otherwise, the hub may be skipping internally simply because the selector chain is too tight and it is stuck between speeds 2 and 3. Just try removing the selector chain to see if the issue stops and then go from there in setting it up again. I always use KMC 8 speeds. It is possible that the chain is possibly not the issue here.

 

[silva]

There must be some damage inside the hub, causing a near-jam of the force transmission, which is in the case pushing on pedals overcome by the applied force, and in the case not pushing / freewheel, not overcome, causing transmission to jam, with the chains mass inertia (=wants to keep going) able to jump off the sprockets, allowed by chain tension slack enough for it.

 

[brommieinkorea]

Hub is out of adjustment. Adjust the chain-screw thingy that goes into the center of the rear hub, per the manual. The hub is getting stuck between gears and refusing to freewheel..

 

[Gunk]

Is it a 3/32” chain?

 

[Willam]

Is it a 3/32” chain?

Yes.

 

[Willam]

Sometimes the hub can cause excessive drag particularly when freewheeling. I have have sometimes found this, particularly when in the 3rd hub gear. The top of the chain will drop onto the chain stay as you coast downhill. I'm not sure if that is similar to the symptoms you are having. Otherwise, the hub may be skipping internally simply because the selector chain is too tight and it is stuck between speeds 2 and 3. Just try removing the selector chain to see if the issue stops and then go from there in setting it up again. I always use KMC 8 speeds. It is possible that the chain is possibly not the issue here.

The chain is not so much dropping but literally jumping up and down quite forcefully as soon as I stop pedalling…I did try adjusting the chain screw a little more but made no difference tho to be fair it was quite stiff so I will try I new one, see if that fixes the issue.

 

[Willam]

Hub is out of adjustment. Adjust the chain-screw thingy that goes into the center of the rear hub, per the manual. The hub is getting stuck between gears and refusing to freewheel..

I have got the position of the chain in the correct place as per the manual but you could be correct, the chain was a little stiff so I will try a new one.

Edit, I guess I can try manual setting of the gear chain to the 3rd hub gear before trying a new chain, see if that works, the chains are only around £10 but worth a try before spending the money.

 

[gizmo1994]

You shouldn't need a new selector chain unless yours has got bent somehow. (easy to do if it is not lined up in the direction of pull before reconnecting to the cable.). Try running the bike with the selector chain completely removed. This should force it into 3rd hub gear. Also see what happens when you back-pedal in each of the hub gears.

I have a similar issue on one of my newer BWR hubs which has only covered about 5,000kms. The chain jumping around when coasting downhill in 3rd. It has stopped doing it so badly now but my next steps if it returns are first of all to check the tension on the bearings and maybe slacken off by a quarter turn.

Next is to strip the hub and rebuild with good grease. This is actually pretty simple despite what some people suggest and I have found some newer hubs to be rather lacking of grease on their internals.

 

[T4tomo]

Does the tensioner appear to be working OK / reassembled correctly from changing the chain?

Chain going slack and bouncing sounds like a chain tensioner issue to me?


*If the selector is selecting all 3 gears with no gear slippage, then the selector is correctly adjusted.

 

[Willam]

You shouldn't need a new selector chain unless yours has got bent somehow. (easy to do if it is not lined up in the direction of pull before reconnecting to the cable.). Try running the bike with the selector chain completely removed. This should force it into 3rd hub gear. Also see what happens when you back-pedal in each of the hub gears.

I have a similar issue on one of my newer BWR hubs which has only covered about 5,000kms. The chain jumping around when coasting downhill in 3rd. It has stopped doing it so badly now but my next steps if it returns are first of all to check the tension on the bearings and maybe slacken off by a quarter turn.

Next is to strip the hub and rebuild with good grease. This is actually pretty simple despite what some people suggest and I have found some newer hubs to be rather lacking of grease on their internals.

Will give that a try thanks.

 

[Willam]

Does the tensioner appear to be working OK / reassembled correctly from changing the chain?

Chain going slack and bouncing sounds like a chain tensioner issue to me?


*If the selector is selecting all 3 gears with no gear slippage, then the selector is correctly adjusted.

Will try this too, I know I previously put it on incorrectly…

 

[Gunk]

Does the tensioner appear to be working OK / reassembled correctly from changing the chain?

Chain going slack and bouncing sounds like a chain tensioner issue to me?


*If the selector is selecting all 3 gears with no gear slippage, then the selector is correctly adjusted.

That’s a good shout, I wonder if it’s been assembled correctly