The Brompton 2 speed derailleur has been designed to have a long service life and Is initially adjusted at the factory and by your Brompton dealer.
It generally only needs adjustment after installing a new cable, fitting new components or after a severe knock or crash.
If you find the shifting is slow in changing between the sprockets, please ensure that the drivetrain is also cleaned thoroughly.
Please note there are several moving parts in this area so be careful not to trap your fingers, hair or clothing.
Check there is no excessive wear in the chain, sprockets and idler wheels, ensuring the idlers are free to spin. The derailleur plate, cable anchorage, and the cable up to the shifter should be free moving.
Any components showing excessive wear, damage or play should be replaced.
The chain should move smoothly swiftly between the sprockets with no resistance. If the limit screws need adjusting, then do this in ¼ turn adjustments at a time. The derailleur plate arms should sit as close as possible to the chain without ever rubbing.
Typically, once adjusted, there should be around 1mm between plate face and chain face.
By gently pulling the gear cable, you can force the derailleur to change gear and see the maximum limits the derailleur will move to. The chain should never drop off the outside of the sprockets. Adjust the screws to ensure this cannot occur.
Brompton original gear cables are supplied pre-cut for convenience and speed, so ensure that you choose the right cable for your handlebar and shifter combination. Cable installation instructions may vary depending on the type of shifters fitted, so follow the instructions and cable routing supplied with the shifters.
The cable end should meet up to within around 2-3 mm of the cable anchorage grub screw. Ensure the grub screw is sufficiently tightened but does not damage the cable excessively. Excess cable slack can be taken up by a barrel adjuster or a stepped ferrule, depending on your shifters.
Balance the cable tension so it allows sharp shifting and release of the chain but does not cause the chain to rub in either sprocket.
It is normal for new cables to “bed-in” so may require additional tension adjustments after the first few rides.
If you have any doubts about derailleur adjustment, please consult your local Brompton dealer