Brompton 2 / 6 speed Derailleur - how does it work?

The original Brompton derailleur system is used on 2 speed and 6 speed Brompton folding bicycles (not to be confused with the 4 speed derailleur introduced with the P Line and used on the T Line and 2023 C Line Electric)
This short video gives a basic description of how it works and some simple troubleshooting tips
Clue: Most trouble is dirt related
If you would like more technical detail - let us know, and we can make a more detailed version
The video shows (in summary)
How the chain pusher / derailleur changes gear
Removal of the chain tensioner
Quick clean of the chain tensioner
Removal (in place) and clean of the chain pusher
Limit screw adjustment

[@dtyn]

“Please ask permission from your significant other when cleaning bike parts in the sink” - this could be the single most important tip from the video LOL

[@therainbowgulag.]

Her presentation style reminds of Watch with Mother when I was a kid in the 60s. I'm expecting Bill and Ben to turn up any minute.

[@rcfokker1630]

I just put a new chain on the Brompton ... the bike has done about 3,500 miles. Did not change the rear sprockets. BIG MISTAKE. The new chain kept pinging off the smaller of the rear sprockets; I couldn't do anything about it. Had to refit the old chain, in the end. Have now ordered new sprockets from you. Live and learn.

[@josephedisonjunior5542]

Can you do a dedicated video on replacing the shifter cable and tuning the rear derailleur for the external 2-speed? How to tune the length of the cable with the barrel nut to match the shift points.Thanks

[@ratoneJR]

Like the video, don't like the proprietary "pusher" system.

[@paullehmor982]

Please make a video about replacement of gear and brake cables! How does the new gear shifters differ from the pre 2017 shifters wrt cables replacement?

[@MiataBRG]

You missed the role of chain tension and how to correctly tension the gear cable.

[@wildwand]

Your videos are easily the best there are for maintaining a Brompton. I am a complete bike novice, but you always explain things so well that I feel confident trying to adjust/mend things myself! Thank you.

[@pianer29]

Thanks for the video, but... Looks like I'm the only one here who didn't succeed. I did everything and still the chain does not jump to the smaller star (+), as if the mechanism still slows down somewhere and does not slip. What to do?

[@andrewmartin5877]

My chain-pusher wasn't properly functioning as I needed to loosen the 2.5mm bolt fitted to the 'dogleg'. Many thanks for the video and hints.

[@portraitonetelo1897]

Am totally new to trifolds. This one brilliant educational video had me figure out how a shifter that had no -/+ indicator window changes gears from high to low by just observing the pull of the chain, movement of the derailleur and the sprocket it jumps onto. Thanks a million and please keep it coming! God bless.

[@TonyOgilvie]

As usual - yours are the Go To Videos for maintaining the Brompton - THANK YOU!

[@darwiniandude]

I really appreciate that you've made the effort to come back and amend the description on this older video to indicate it doesn't apply to the new 4 spd :)

[@cesarbadell9780]

Best Brompton’s Knowledgeable channel on KZbin!!!!

[@feedmetofu]

Thank you for clear explanation and supply of sprocket & chain, along with the tools needed. Took a little bit to find the source of the problem but once adjusted as you described and replacing chain & sprocket - it shifted so smoothly, i didn't even realise.

[@JH-su3rn]

Thank you! Chain fell off my daughter’s Brompton and didn’t know how to get it back on the derailleur. Watched your video and got it back on easily🙂👍

[@diane1959]

Thank you for this video. It is the only detailed video on how to set up the chain pusher that I have found. You saved me a trip to my local bike shop.

[@rbranch234]

“Please ask permission from your significant other when cleaning bike parts in the sink” Wonderful. Not an issue for me though, since I live alone and make sure I don’t do this type of thing when the kids are visiting.

[@davidash8403]

Had an issue with the gear changer/derailleur and your video hit upon all the things you could do to make it right. It worked. Thank you!

[@cswjames]

thanks for putting this out there. really helped me, as a novice, to install a new shifter and anchorage and then get it adjusted. cheers, chris