I have had a 'Deore' equipped mountain bike for 3-4 months now. However, there is grinding noise from the area of the cranks and I suspect the bottom bracket.

On a local MTB forum I heard that Deore BB's last exactly that long. So I am worried about replacing the part with an exact duplicate (for fear of short service life).

Do more expensive Shimano groupsets use the exact same BB or is it different for each? Do they last longer? Is it normal for a Deore BB to fail after such a short time?

  • 5
    A BB should only last 3-4 months? Seriously? – Benedikt Bauer Sep 1 '14 at 14:54
  • I got it replaced under warranty. The bike had been handled as is normal for an MTB: some rain, lots of mud, some careful washing with hose under pressure, some salty air from around the sea. The BB was so badly rusted/worn, that the cranks wobbled, plus a handful of red powder poured to the ground. – Vorac Oct 1 '14 at 15:54
  • 1
    Pressure washing with a hose will destroy sealed bearings. – Fred the Magic Wonder Dog Sep 21 '15 at 23:56
  • 1
    This might be helpful on the subject: bikeradar.com/gear/article/… – Vorac May 31 '16 at 15:01

There are a number of options for replacing a Hollowtech II BB (whilst still retaining the Shimano cranks). The Deore bb is a cheap bb, higher Shimano levels should last better. Anecdotally I've heard premium Bb's last years while it's not unusual to use a Shimano BB a season.

The options are:

  1. Shimano - Shimano has a number of different levels. BB51 deore level, BB70 SLX/XT and BB93 XTR

  2. Other similar brands - Raceface X-type is compatible

  3. Premium brands - Hope, Chris King and others

  4. Hacks - replacing and upgrading the bearings while retaining the Shimano cups.

If you kill many bottom bearings it's good to understand why and address this. Water retention in the shell is a big issue if you ride in wet areas as is washing the grease out with a pressure washer. There are Bb's that have water drains built into the cups for drainage or you can drill a hole in your Bb shell if this is a real issue for you. Sealed bearings offer better water protection.

End of the day it's really a value choice, if you go through a lot of Bbs you should consider a premium one.

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  • 2
    Yeah, but if you're going through a BB every 3-4 months, its almost surely that something is wrong. Also, note that for one premium BB, you might be able to buy enough BB's to last the life of the frame. – Batman Nov 1 '14 at 14:28
  • The mechanic at the shop expressed an opinion that Deore and above are not optimized for long life, they are made to be light. And indeed (from here on, my personal observations), plain old square taper sealed units last much longer in the rain and are cheaper. – Vorac Nov 3 '14 at 9:32

I would say you've been unlucky to have it fail (if it is definitely the BB that is the issue) in a short space of time. I'd ask for it to be replaced under warranty if it's only a few months old.

More or less each groupset has it's own BB. You can get higher-end BBs (XT, XTR). Reality is, they don't do much but if you're unlucky and get a bad one then they'll creak, grind, clunk etc and make you aware that's something's not well.

Compared to other parts of a groupset, they're one of the cheaper parts and straightforward to replace, particularly the Hollowtech II. The more expensive models are typically a bit lighter and have a different ball-bearing design/material.

I've had my Stumpjumper FSR for six years now and I've replaced the BB twice. The XT model has worked well for me. I've ridden in a very wet and muddy England, Wales and Scotland; and this BB has met the task admirably.

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  • And do you know if they are interchangable i.e. can I put an XT BB or I need to get the exact same as the current Deore? – Vorac Sep 1 '14 at 14:35
  • I believe they're interchangeable. With BBs you need to make sure you get the right thread (English or Italian). Certainly a quick Google suggests it is possible but check with your Local Bike Shop if you're not sure what you're looking at. If you like being hands-on and want to save yourself a few quid then buy the tools and learn how to maintain your bike yourself. There's plenty of good YouTube videos on nearly everything. – adey_888 Sep 1 '14 at 14:44
  • My guess is that you don't need worry about Italian/English with an MTB bottom bracket, certainly not any MTB made in the last 10 years. – Fred the Magic Wonder Dog Sep 1 '14 at 16:46
  • Check the width matches. – James Morris Sep 2 '14 at 23:17

BB51 and BB70 are interchangeable. The hole is the same, they both fit perfectly. Unfortunately mine BB51 is giving out noises after 0.5 years, so I guess this is common. Before that I had BB70 and it lasted thousands of miles.

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  • In fact, You can go for BB90 because BB70 and BB90 are interchangeable according to shimano tech docs. There is no official confirmation about BB70 vs BB51/BB52 but I think they just don't want to admit it. – egils Sep 20 '15 at 10:21

I have ridden thousands of miles on the original Shimano sealed square taper units, road and MTB, and never had one fail. Early FSA external bearing crank, garbage; same with the Enduro ceramic scam, so poorly made the bearing was not able to spin freely just from press fitting into the external cup, using their cup and their tool. Shimano Ultegra was an instant improvement, works after several years and am going to try the newest sealed upgrade - at $25-35, there is zero justification to waste $$$$$ on any other brand. If you get worried, you can pry out the bearing seal, clean and re-lube with good grease and go again. MT800 is the sealed mountain bike version as well. One caveat, is that all of these require the frame actually have a proper facing tool run before installing, as external cups are awfully sensitive to the outside BB faces being parallel. The old integrated square taper units were not, as they contained both bearings in a single sealed can that threaded into just one side of the bottom bracket. If you are dealing with any newer pressfit type, good luck.

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