Tnrc 2011

My Brompton is now fucked. Refuses point blank to shift into the smaller gear*. I did a thorough clean-up, and I've even had the adjustable wrenches out. Singlespeed for now, till I see what a mechanic has to say :/

*it had always been somewhat reluctant to move into the non-stock 15t, even though it's the same model of sprocket they use with their stock 16t

Sounds like the chain pusher isn’t moving fully to its upper limit point, or this point is not adjusted correctly. It may need more cable tension, or the grub screw in the dog leg may have been overtightened, lengthening the whole assembly. You'll need to check that with the chain tensioner removed, the chain pusher moves fully and crisply from stop to stop and that the idler wheels are free to move side to side on the chain tensioner.

PM me your email and I'll email you the exploded diagram with some instructions.