As I said, I have a 1972 Centurion. Today while riding I hit a pothole as I was coming down on my left pedal. I immediately felt like my pedal was moving around in ways it shouldn't. Stopping to look, I'd cracked the actual axle that the crank arms attach to.

I'm looking for information on where I can buy a replacement part for this, how much it will cost, as well as how to carry out the replacement.

Here's the actual crack: cracked axel

Here's the pedal looking all bent: bent pedal

  • Yeah, the bottom bracket assembly needs to be replaced. This is axles, bearings, and cups. At that age it would not be a cartridge but loose bearings. There are several different styles, but likely this is a common one and a bike shop can fix you up. (First time I've ever heard of such a failure.) Oct 3, 2015 at 11:58
  • (Oops -- make that "axle" (singular).) Oct 3, 2015 at 12:58
  • 1
    This is totally impressive, by the way. I've seen broken bottom brackers on mountain bikes but not on a road bike. Gnarly. :-)
    – RoboKaren
    Oct 3, 2015 at 22:50
  • Riding would be very dangerous. If the axle snaps the edge of the break is razor sharp. and your calf is likely to meet it because it will happen when your left leg is moving down. (speaking from experience) It's going to leave a nasty cut!
    – Carel
    Oct 7, 2015 at 18:37

3 Answers 3


The crack is in the bottom bracket(BB) axle. This will at least need to be replaced. If the crank arm(silver part) is not damaged this can be reused.

There are many types of bottom bracket standards but it is most likely this frame has a 68mm English thread square taper bottom bracket which are the most common in pre year 2000 bikes.

Something like a Shimano UN26. Any bike shop should be able to supply and fit a new bottom(price in my local area would be $30-50 supply+fit). You do need specific tools to remove and fit bottom brackets so unless you plan on investing in some tools I suggest get a shop to replace it.

  • Thank you for the correction on my terminology, I've really only begun riding recently and a quick look at a diagram had me thinking that the broken part was the "crank axel", but knowing it is in fact the bottom bracket axel will help my search greatly. Given the cost you suggested, I am favoring letting my local shop fix it. Oct 3, 2015 at 22:52

I would not ride that bike, as pictured.

How to fix it? I shattered a cup on my old MTB. The fix was to take the bottom axle into a bike shop and they couldn't supply the right part, so I bought a sealed cartridge instead. It went in easily, needs no bearing tweaking, is waterproof and brilliant.

Only downside is you'll need these tools:

  • 14 mm socket to remove crank bolts/nuts
  • Crank remover to get the cranks off (do both sides now)
  • Sliding lock pliers to remove the lock ring
  • Big spanner to remove the cups
  • Cleaning products and rags to clean the hole and threads
  • A drive socket that suits your new bottom bracket cartridge

If you are handy, buy the tools and be set for life. Otherwise get the LBS to do it.

A mid-range shimano one cost me $50 NZ and has been one of the best upgrades to my old bike.

BTW you ride a bike thats older than me - that's impressive. Thank you for not contributing to the throw-away society.

  • thank you for the brief rundown on required tools. I'm weighing the cost of those against paying a bike shop to do it. Also, thank you for the kind words regarding the bike; I inherited it, and I find it functional and rather charming so I see no reason to get rid of it : ) Oct 3, 2015 at 22:49
  • @lelandbatey Buy the tools if you can afford it, you'll have them for life. I bought a special freewheel removal tool for an old "suntour perfect" 5 speed freewheel, and ended up using it again 6 months later.
    – Criggie
    Oct 4, 2015 at 4:04
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    Most crank pullers include a socket, so that can be skipped. Oct 4, 2015 at 4:14
  • @MikeBaranczak ZOMG I never realised that! I figured it was just a way to save metal, and I remember grumping that it should have been a half-inch square drive. I have learned something today.
    – Criggie
    Oct 4, 2015 at 5:04

If you're replacing the BB yourself, just make sure you get the right one. You need to consider the following variables:

  1. General type (we already know it's a square taper, so no problem there).
  2. The width of the shell (the painted part) - that's easy enough to measure.
  3. The length of the spindle (axle) - you'll have to remove the cranks to get an accurate measurement.
  4. The thread type. Centurion was an American company, so it's probably English threading, but I can't guarantee that.
  • Thank you very much, this is precisely the type of information I am looking for. This will aid my search tremendously! Is there any place in particular you'd recommend looking for bike parts online? Is Amazon a decent option, or is there some other retailer that's generally better for bike parts? Oct 4, 2015 at 21:49
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    When you're buying through Amazon or Ebay, it can be hard to tell who you're dealing with. Ebay is good for used stuff, if you know exactly what you're looking for. Your best bet here is probably a local bike shop - if you have any questions, you'll be able to talk to a real live human. The one brand I'll recommend is Park Tools - their stuff costs more, but it's totally worth it, and it lasts a lifetime. Oct 5, 2015 at 1:48

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