Thread: Bottom bracket BB UN50 replacement
View Single Post
Old 09-13-23 | 07:14 PM
  #6  
maddog34's Avatar
maddog34
Senior Member
10 Anniversary
Community Builder
Community Influencer
Active Streak: 30 Days
 
Joined: Jul 2015
Posts: 7,382
Likes: 3,226
From: NW Oregon

Bikes: 1982 Trek 930R Custom, '91 Diamondback Ascent w/ XT, XTR updates, Fuji Team Pro CF road flyer, Specialized Sirrus Gravel Convert, '09 Comencal Meta 5.5 XC, '02 Marin MBX500, '84 Gitane Criterium bike

i suggest that you read the links i posted earlier, and also read this link..

https://bicycles.stackexchange.com/q...aper-cartridge

the UN-50 specified by Trek is a compromise unit meant to cut the cost of the bike... and the LENGTH is mostly determined by your frame's design. Emailing Trek may be the only way to know what length they installed in your frame for that particular crankset... Another possible way to find a possible length would be to Look Up the Part Number of the crankset on the bike and hope Shimano has recommended a specific length for a typical MTB.... the kicker being that your 8900 is NOT really a "typical MTB".

there is not much rhyme or reason to the UN designations, other than to identify their Model class.. the usual groupset BB for your XTR parts Was a UN-91, if i recall correctly... the spendy one... there's a NOS one on Ebay right now for $250... and some others too.

And i can't stress this enough.. you might NOT NEED A Bottom Bracket assembly..... those bikes have other "noise" issues described in one of my earlier links.

i'm out..
Last edited by maddog34; 09-13-23 at 07:20 PM.
maddog34 is offline  
Reply
0