Brompton Derailleur Problem

[SteveStockholm]

I have a 6 speed Brompton (2018) model. The high/low shifter is not shifting the chain to the smaller, outer, high gear sprocket, it is stuck on the bigger, inner, low gear, sprocket. I have dismantled, cleaned and oiled the chain tensioner and it’s wheels, and the chain pusher itself. I also took apart the shifter. Still I have the same problem. when I move the shifter, the chain pusher seems to move a decent amount. Any thoughts on what the problem might be? Adjustments - is there something to tweak?

 

[Gunk]

It may be that the cable is too tight.

 

[steveindenmark]

How odd. I have exactly the same problem on my 6 speed. You need to join Brompton Folding bikes on FB.

Click the link it may help with your problem.

View: https://www.facebook.com/groups/220466801332012/permalink/3168269116551751/

Watch this.

View: https://youtu.be/EwYEYO3h2Po


View: https://youtu.be/pLtSNEz2Ixo

 

[SteveStockholm]

It may be that the cable is too tight.

Yes, that make logical sense, as the spring must be pulling the chain away from the small sprocket. The adjuster on the shifter end seems as loose as it can be, is there another adjustment?

 

[SteveStockholm]

Continuing problem with Brompton Derailleur on 6 Speed.

I am still having problems getting my Brompton to switch to high gear (small sprocket). This is what I have tried so far:

• Removed, cleaned and oiled chain tensioner - wheels are turning freely and wheels are moving in and out freely.
• Removed, cleaned and oiled the chain pusher - some signs of wear, but generally seems ok.
• Dismantled the high/low shifter and followed advice on the you tube video about sanding the inside of the ratchet which might stick due to expansion. Greased and reassembled. The only point worth noting is the cable tension seemed much looser in the video - not sure if this is significant.
• Spent a couple of hours playing around with the limiter screws on the chain pusher. The chain still does not move far enough to push the chain to the small sprocket but if i pull very slightly on the an allen key maybe 2mm, it does derail.
• I checked that cables going to the derailleur are all attached to the frame correctly, oiled and that the spring is clean and oiled.
• Have checked that screw connecting pusher to the spring is not overtightened.
• I also played around with the cable tension adjustment at the shifter end, but that only makes the spring tighter - so the wrong direction.

I am sort of out of ideas of things to try now. Is it possible that the spring has become too compressed and does not travel as far back as it used to? Any other suggestions?

 

[thisonetimeyah]

Hey did you manage to solve the issue?

I have the exact same problem on my 2017 S2L. The shifter doesn't shift the chain to the smaller, outer sprocket. It's stuck on the higher gear.

I've watched the same videos and spent ages going through each of the steps, cleaning and oiling the chain pusher, the jockey wheels, and the shifter mechanism itself.

I'm almost certain that the issue lies in the cable tension. It fails to slacken enough for the higher gear (or the chain pusher fails to move enough once the cable has been slackened, though I suspect it's the former).

My S2L is pretty unused as well so it's highly unlikely to be caused by worn parts or gunk. I can't seem to figure out how to reduce tension in the gear cable. Any ideas?

Did you manage to get yours functioning?

 

[Gunk]

I would start by disconnecting the cable and see if the derailleur by default springs back to the smaller cog. The derailleur is under tension when the chain is on the larger cog. To me it sounds as if the derailleur itself is stuck.

 

[thisonetimeyah]

It was definitely the cable being too taut. I slackened it at the gear shifter end and the derailleur sprung into default onto the normal cog.

At least that issue is semi-diagnosed, but as a result I've run into another one.

In releasing tension by twisting the plastic cap over the gear cable nut at the shifter end I seem to have released the cable entirely and don't know how to get it caught by the nut/cap again.



Please help.

 

[Bromyboy]

I have found when folding the Brompton, the cable stretches and gets caught where it enters the shifter housing. It happens on my six speed 2018 model. I would suggest selecting the small cog before folding the bike. Hopefully this should help.

 

[Dr T]

Ho, i have an older Brompton (2009)….
Following the brilliant Brilliant Bikes video i have taken apart, cleaned and reassembled my dereilieur….however, i still have a problem that although i can shift into lower gear (big cog) nothing clicks and so it just immediately shifts back to high gear as soon as i let go of the gear chamge thumb lever.

Does anyone have any ideas what might be wrong?
Thanks.
Tim.

 

[Jemtaylor]

I had this problem too. Tried stripping, cleaning and lubing everything. Dismantled the shifter. No good.
I figured out that it might be the spring that has got 'tired', so I replaced the 2 speed dog leg assembly and I also changed the cable while I was at it. This seems to have fixed it.
Comparing the old and new springs it looks like the old one wasn't pushing enough any more.