Apr 12 2010
Changing a bottom bracket – a black art.
Your pedals wobble and it’s not a loose crank, so it’s probably the bottom bracket (it’s “BB” in cycle-shorthand) – what do you do:
A – keep pedaling until something catastrophic happens.
B – panic and call the local bike shop.
C – fix it yourself.
When it happened to my old MTB last year I chose option “B”, which in hindsight was probably right, as they had to use a lot of heat to get the old BB out and then respray the frame to get it back together, all for the original quote.
But when my Cannondale hybrid BB started to wobble a few weeks back I went for option “C”. I’ll let Sheldon Brown explain some of the intricacies about bottom brackets – suffice to say that for the majority of Shimano-equipped bikes, the BB will have a standard diameter, so all you need to measure are the width of the bottom bracket housing and the width of the spindle to ascertain what size to order. Alternatively you can just take the old one out and check what’s written on the inside of the BB.
Removing a bottom bracket is where the panic is likely to set in, but rest assured it’s really easy. You will need the Shimano BB tool, which costs about £12, and a very large adjustable spanner (or plumber’s wrench), but once you’ve got those the job is really easy.
There’s a small caveat – if the bottom bracket has never been changed and/or the bike’s had a hard life, then this job could be considerably harder, involved copious quantities of WD40 to loosen the threads… but then, nothing ventured, nothing gained.