Sealed bottom bracket replacement

DrewSavage

Retro Guru
Hello, I'm hoping someone might be able to offer me a quick bit of advice, I've ventured out of my comfort zone (which is basically anything beyond adjusting brakes and gears on old road bikes.

I've got an old Raleigh Yukon that I use for getting around town which is creaking from the bottom bracket - fairly sure the best long term solution for someone with my level of tech skills is to replace it with a modern sealed unit like a Shimano UN-55, but I'll admit I have no idea what size to get.

Someone told me basically just replicate what's on there already so I tried to measure the axle length without removing anything and it seemed to be about 140mm, yet I had a quick Google and the longest these seem to come in is 122.5mm.

Am I barking up the wrong tree, are the UN-55s only for road bikes and there's an MTB equivalent I don't know about?

http://www.chainreactioncycles.com/mobi ... 7C271964UK
 
Re:

It's possible that you are measuring the whole length of the bb. (Usually you do)

But, On those older ones there is a threaded end. Ignore the threaded bits and measure where the square taper drops off.

I reckon that you will end up around 122 mm. Quite a typical size for steel frames in that era.

Cheers
 
Re:

By the way.

If you can find them, un72, 53,52 etc....are generally better.

Those un55's are heavy, tight and clacky.

I'm sure you be sorted easily enough.
 
Re:

In addition to the axle length, you'll want one with the correct spacing for your bottom bracket shell. It will be 68 or 73mm.
 
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