Should I replace my 12-year old bottom bracket ?
 

Yeah,yeah, I'm aware this is a perennial question, and I'm also aware of the old adage, "if it ain't broke, don't fix it", but there's also something to be said for preventative maintenance, which is where I'm at now.
I've already searched the subject on the interwebs, and answers varied widely, so, here's the deal.......I have a 12 year old Deore-equipped Trek mtn bike, that I got on Craigslist about 8-9 years back, I'm plenty happy with it, and last year I put a solid set of new wheels on, and replaced a glitchy right shifter (as well as a new chain and cassette) .
Since I've observed that some further details should be included: I weigh 200-210-ish but don't ride it particularly hard at all. I have it set up as a road warrior, just doing steady, cardio/calorie burning rides, no off roading other than the very occasional dirt road.
It's never been rained on since I've had it, or been immersed in a creek, or power-washed, or anything like that.
I seem to recall having some creaks when i first got it, and pulled the cranks, cleaned and re greased the BB threads, and been fine ever since.
So, are these things generally good for thousands of miles, or is 12 years not a bad time to consider replacing the BB ? ( I e-mailed Trek to find out which one I'd need, then found them on-line for $22 delivered, so cost isn't really a factor).
thanks in advance for any good info or advice........

Seems you know the answers and don't like them. Yes, BBs are good for thousands and thousands of miles; years hardly matter. But it's OK, it's not a moral issue.

Proceed without deceiving yourself. BBs tend to give lots of warning so preventative maintenance doesn't mean much. Budget for one or two special tools and a torque wrench and there's always risk of damage. Good luck.

Maintenance ..
 

If it can be removed, cleaned, inspected , If loose ball type, buy new ball bearings, re grease and put it back together..

Taper BBs can last forever if not abused. Particularly decent quality cartridge units. Sounds like yours has lived an easy life. Take the arms off and feel the bearing, unless it is gritty or making noise--it is probably fine.

I wouldn't.
Replacement is such a simple job, the thing could disintegrate and with next day shipping, you could be on the road again.

Even though I'm just asking a simple, reasonable question, I was already aware that I'd likely get some snarky, smart-ass, attitude-filled responses, but I'd hoped it wouldn't be the very first one. It's not that I "don't like" the answers, it's that (as i clearly said) the ones I found were widely ranging, from 1000's of miles, to as few as 4K.
And, as I also clearly stated, I already pulled the BB ( and therefore, obviously, the crank), so it's a fair bet I already have, or at least have access to, the tools. No need to budget them in.
And preventative maintenance actually does mean something, especially given that I'm talking about entirely replacing the part that you just said was good for "thousands and thousands of miles".
Anyway, thanks to Fietsbob (and Marcus and Bill) for posting a polite, helpful answer. I'm thinking the BB is a sealed/cartridge unit, which may still be possible to service, but aren't really designed to be (as i'd read). And again, for $22, I'd just as soon replace the unit if i'm gonna mess with it. But, as Ankle-Biter pointed out in his rude, convoluted way, I'm probably good to go for a while.
BTW, any idea of what size ball bearings a Shimano BB would use? I have a small stash of good bearings for hub re-builds

If it's a cartridge BB there are no reasonably user serviceable parts inside. Toss the old and drop in a new UN 55 of the correct length.

If it's loose ball, usually 1/4" balls

Quote: Brocephus

"And, as I also clearly stated, I already pulled the BB ( and therefore, obviously, the crank), so it's a fair bet I already have, or at least have access to, the tools. No need to budget them in.
BTW, any idea of what size ball bearings a Shimano BB would use? I have a small stash of good bearings for hub re-builds.


No need to tell you the answer. You clearly should know since you have already pulled the BB.

Yeah.....about TEN years ago. Obviously, I forgot, or wasn't paying attention to that at the time, hence my question. And since it's already been answered, why are you even weighing in ?? Go be dick somewhere else.

Thanks for the solid info. That UN55 is what Trek recommended. And, yeah, it's my understanding that sealed/cartridge type bearings aren't usually user serviceable, though I came across several posts around the internets from guys saying it was doable, but I wouldn't give it a shot myself,especially not with a new one being only $22.

Actually dick is not my name, but AH are my initials. Have fun with your new 1/4 inch balls.

If there's nothing wrong with the cartridge, there's no need to do anything. It's not as if a BB failure is going to leave you stranded; might be noisy riding home, but that's about it. Run it until there's something obviously wrong (noises, rough rotation, etc.) and replace it when that happens.

Very good advice IMO. Run it till it gives up, then a quick switch out and good to go for another very long time.

If it works, don't replace unless you go to a new crank with external bearings.

No offense, but it sounds like you have an opinion already and want us to confirm what you already want to do and then get mad when our opinions differ. In a forum, or in the real world, when you ask a question you will get a variety of reasonable opinions. Ultimately you have to weigh the responses and make a decision.

You have our permission to replace it. You also have our permission to keep it. Either option is not a big deal with huge pros or cons.

I don;t know where you're getting the idea that I came here with my mind made up, and that I'm angry about dissenting opinions. I pretty clearly implied I was on the fence and looking for info, when I said I was, "aware of the old adage, "if it ain't broke, don't fix it", but there's also something to be said for preventative maintenance", and though i was originally leaning towards replacement, I then acknowledged in my next post that I was, "probably good to go for a while", based on the first few replies. Obviously I was neither set in stone, or angry with differing views.
What I am getting annoyed with are the obtuse, wise-ass, unhelpful comments. I've "thanked" all the serious replies, regardless of perspective on the question.
But I'm eagerly standing by for the next wave of comments from the reading-comprehension-impaired. :D

I have shimano square taper on two bikes and each has over 24000 miles. If you were going on a week long or longer you might consider it. If not ride it until it gets noisy.

My gauge for deciding whether to mess with a bottom bracket is to remove the cranks/chainrings and twiddle the axle with my fingers. If it feels smooth without excessive play, I leave it alone and keep riding. Every time I've disassembled a bottom bracket to inspect it, even with 30+ year old bikes, the BB was fine. At worst I might need to adjust the tension to eliminate slack without grinding from excessive compression on the bearings.

There certainly is something to be said for preventative maintenance, but I don’t think it applies here. Preventative maintenance is addressing a potential problem before it becomes a big problem - fixing/replacing something to reduce the likelihood of it failing catastrophically and unexpectedly somewhere down the road. The obvious example would be brake/gear cables. But BBs don’t fail catastrophically* - they get noisier and rougher over time, and will eventually die. What you’re proposing - replacing a used but still functional BB in case it fails at some unpredictable point - is akin to replacing a tire at 1000 miles because theoretically a slightly worn tire is more prone to puncture than a brand new tire. At most, I might have a replacement BB on hand to swap in when/if it starts to play up, but even then, it’s demise will be so slow and unsurprising that ordering a new one when needed makes more sense. Why tie up funds in something that might end up sitting on the shelf for years?
* well, almost never

When I was in high school I decided to clean and re-grease the bottom bracket bearings. When I put the littles balls back there was a big gap. I thought I lost one so I put another one in I had. After a few days I could hear them grinding together. The bike was never the same after I serviced it.

Okee-doke, thanks guys, I reckon I'm good here. Sounds like the consensus is that these things last nearly forever, and I should leave well enough alone, which works for me.
Thanks again to all for weighing in ( yeah, even the arse holers !!:D )

Shortest answer:
No need to preventively replace them.


Longer answer:
Cartridge square taper BBs last for years and tens of thousands of miles - often, even in harsh riding conditions.
As long as there is no play, or creaking-hard to turn resistance (which is practically never the case, usually the play is the first indicator of a square taper BB bearings failure), they are good to go.


Very long answer:
Tricky part about square taper BB-s is the failure mode. If they fail suddenly, it's usually at the place where the cranks are attached - and within the area covered by the cranks. It's a fatigue induced failure. And no one can tell if it will happen on the first month with a new BB, or after a year, or two. Checking periodically would mean weekly, or at least monthly (depending on mileage) removal of cranks, cleaning, inspecting for cracks, then re-mounting the cranks. Which is not something that sqare taper interface takes fondly - so you are more likely to ruin the axle-crank arm interface more quickly, getting play, cranks coming loose.

This does not happen often, nor regularly, but it is the thing I don't like about square taper cranks. I'm yet to have a Shimano square tapper BB fail like that on my bike, but I have seen one on a customer's, then investigated it to see if it's preventable, or at least possible to be spotted in time. Turns out it's very uncommon, but can't be prevented since regular (enough) checks are not practical.

More modern Hollowtech II axles are easier to check periodically - there the weak spot is the place where the axle contacts the BB bearings. In case of a bearing failure (seizing, or turning with difficulty), axle gets worn at the bearing contact spot (since only the axle is turning) and that wear leads to a (sudden) crack - in time. Inspecting these monthly, or at least checking if bearings are turning smoothly is more practical and won't cause any harm (except for taking the time). High end (lighter, thinner) cranks and axles are more likely to suffer from this.

Hollowtech II bearings are placed outboard, not inside the BB shell, so they get a lot lower mileage and will stop turning nicely more quickly than square taper BB-s - lasting about 1/3 of the mileage (depending on riding conditions of course). Not too expensive to replace, but still costing more than square tapper, and not lasting nearly as long, especially in bad weather riding conditions, or off road.


Other parts that fail - crank arm at the axle interface, chainring to crank arm interface and pedal to crank arm interface all show visible cracks on the outside - just wipe off any dirt and inspect for hairline thin cracks regularly.
Pedal axles of low quality pedals are an exception, these are also not showing visible wear signs on the outside and I've had (cheap, low end) pedals break at their axle - suddenly. But any good quality brand is yet to do that, without first showing visible large play and stopping to turn normally (without sticking). Even then - I've always had to replace them for wear, never had them break.


The problem with these parts breaking without a warning is if you are riding with some power (especially if out of the saddle, "standing"), and the resistance (pedal) beneath your foot disappears, the whole bike will swerve to the side that had failed - and if there's a car overtaking you on that side, or a cliff, you could get injured.


P.S. When replacing BBs, do use anti seize on the threads, not grease, it offers long-term prevention from seizing, unlike grease. Same goes for mounting the cranks onto the axle and pedals onto the cranks.

I have a bike with a custom frame that was built for me almost 40 years ago. It has a square taper, loose ball Zeus bottom bracket. About 10 years ago, maybe even more, I bought some new wheels that could take a 10sp cassette for this old bike. In the process, I checked the BB, opened it up, put new grease, closed it and smooth as buttah. Well a 10sp cassette and chain didn't mesh well with a 6sp chainring, and I had a 10sp Chorus crank and BB, with sealed bearings, but still square taper. I tried to remove the old BB, but I didn't have the tool for the drive side, so I decided to leave the old BB on it and just put the Chorus crank on the old Zeus BB. I rode this bike the other day and it is still as smooth as ever. My son "adopted" this bike as his own, and he rides the crap out of it.

The moral of the story is that these things last forever, whether cared for or abused.

I will also mention that I bought a Trek 7000 mtb from 1990 on eBay a few years ago. The BB was a little loose. On this one I opened it up and replaced the bearings and put it back together. It is now my regular commuter bike and I never give the BB a thought.

There is also the fact that while the bb may be perfectly serviceable now it can seize in there and be a real pain to remove when you do need to.
It's been in there ten years so I would remove it and grease the threads and reinstall.
But that's me.
Preventative maintenance.
If it is seized now at least you know and can make a plan.
If it's not, great.