Shimano UN54 bottom bracket plastic cup failure #cycling

The cup came loose and with no way to tighten it on the road it kept loosening and jamming the cranks. I eventually gave up, cycled through it, crunch, crunch and the plastic was mangled, but I could finish my ride to work then home in the evening.

As I’ve done before, my Nexus bike donated the parts to fix bluebell, its bottom bracket is UN54 too. Different models often have slightly different cups, so I am fortunate they are the same model.

I’ve ordered a UN55 for the replacement, that has alloy cups on both sides, I’m unsure if that’s wise, but only time will tell if I ever get it happen again.


4 responses to “Shimano UN54 bottom bracket plastic cup failure #cycling

  1. Hope you get it sorted, I’d cry like a baby if it happened to me on my commute! Wouldn’t know where to begin to fix it. Good luck

    • Without the crank pull and shimano bottom bracket tool plus big spanners there was no way. So mangling it was the only option. I’m hoping I’ll be able to tighten up the alloy cup so it won’t come loose. Stupid plastic.

  2. When you put the alloy one in put a bit of loctite threadlock on it, it’ll not come loose again.

    • Hi Jeff, thanks for the tip. Would that work with the plastic cups or are they just a waste of time?
      In the past I’ve always had the opposite problem of not being able to undo the LHS cup.

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