UN300 - less than 300 miles and it's toast

Ugo51

Retro Guru
Hi guys,

I just wanted to report my latest encounter with a defective bottom bracket. I purchased a Shimano UN300 for my Boardman and installed it just before going back home for the Xmas holidays. I did about 150miles before the holidays and 150miles since I am back. This morning I noticed the non-drive side bearings are loose. I haven't taken the BB off yet - will do tonight - but it seems the bearing are toast.
Very strange.
I will (hopefully) know more once I examine it, but I am very surprised about this.
Of note, I recently purchase another UN300 and it looks quite different from that one I bought in December, so I am starting to suspect one or the other is not a UN300...

Will keep you posted.
 

Tootyred

Senior Retro Guru
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Thats interesting to hear.

I trashed a un300 last year, its the first shimano bb ive ever had go so quickly.....from fine to wobbling about in one ride. It was second had, but was said to have done less than 50 miles......it certainly looked like new and to be honest it was so cheap I'm not complaining!

The drive side bearings went wobbly on me after about 500 miles. Originally i thought it might have done more than the owner had said, but im now starting to wonder....

I thought it had come loose to start with, but the movement was rubbing the chain on the front mech. When i took it out the drive side bearing had movement in it.
 

Woz

Old School Grand Master
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It's a sad state of affairs. Have in mind, for about 20+ years Shimano is not offering any decent square taper crank, and I suspect these UN300 are intended to be matched to very low end dross like Tourney or whatever.
 

Woz

Old School Grand Master
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.....and those threads are 10 years old. Without going into Royce and Phil Wood territory:

Concerning Shimano, it's best to get some NOS or very good condition UN7x or UN5x, stock up when you can.

Tange and Token still make quality BBs:
https://www.tokenproducts.com/bottom-brackets/threaded/jis-square-taper-1

Stronglight JP400 is popular with industrial cartridge bearings, but a few notes:
- Older models seem better quality, perhaps those made in France many moons ago.
- I took a fairly recent one to pieces and found it was actually a NECO which seem to have a decent product line and available cheap.
 

Jonny69

Senior Retro Guru
Good to know this about the new UN300. I’d better hoard my two UN55s.

Those cheap Neco square tapers with the alu cups and hollow axle are surprisingly good. I put 11k miles on the last one on my fixed gear bike before the bearings needed changing. You can tap them apart, too, so theoretically you could replace just the bearings.
 
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Ugo51

Retro Guru
I honestly think this was a bad copy. I refuse to believe the overall quality of the UN300 is so low they only last a few hundred miles.
I installed a new one and took the occasion to put back the 170mm cranks. Let's see how long it will last for...
 

CassidyAce

Senior Retro Guru
+1 for the Neco BBs. I put a cheap one in my commuter and, three years later, it's still riding as it was when new. No long mile-munching rides but lots of short journeys through all weathers (rain, snow, even sunshine!) and a fair dose of sea air.
 
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