Brompton 3 to 6 speed conversion

a camping gaz torch puts much less heat into the job than brazing

Eden used a camping gaz torch for the modification

Since Eden Fowler got in touch with his excellent write up and photos of his 1990 Brompton M3R, he has now done what he said and converted it to to a 6 speed bike. So I guess now it is 1990 Brompton M6R! Is there no end to this man’s talents? If you have an older Brompton 3 speed bike you may fancy doing your own Brompton 3 to 6 speed conversion. Read on, this is great…

I thought I’d add a PS to my last offering when I was seeking a more recent rear frame in order to enjoy the six gears that fitting the derailleur permits. Well, to cut a long story short, & after sounding out a lot of sources of Brompton lore, I decided to go it alone & modify my 1990 rear frame to take a Brompton derailleur.

The finished Brompton frame modification

The finished Brompton frame modification

The essential piece is not available from Brompton so I put a 5mm thread through the centre of a short piece of 14mm diameter mild steel bar and then filed it to the tube profile at one end and a hexagon to take the  “Chain pusher wing plate” at the other end. I took into account the very modest loading on the chain pusher, & chose silver-soldering as the best means of fixing the piece. It can be done with a simple camping gaz torch and puts much less heat into the job than brazing. A washer also had to be silver-soldered to the original cable guide to act as cable stop.

So, Black Beauty now boasts a new BWR 3-speed hub plus Brompton derailleur and what a difference it makes! Bodgineering has triumphed again!
{ 0 comments… add one }

Leave a Comment