Hollowtech 2 - Bearing Change





Introduction: Hollowtech 2 - Bearing Change

My quick description how I wrestled with Shimano bottom bracket in order to replace bearings rather than spending money for new cups/bearings set.

The story began with BB-4600 which seems to be fine for 6 months, and then suddenly, at one evening after ride I realised that whole drivetrain is not spinning freely as it should. Quick inspection revealed that component which apparently should be quite robust died quietly. Left bearing in bottom bracked spins but with grinding feeling. After quick calculations was obvious that I need another one in order to keep my wheels rolling. Eventually decided to make a small experiment. I decided to replace bearings in old cups, and slightly upgrade them in the same time.

Step 1: Find Decent Bearing!

The first step was to find out what size of bearing I'll need. After quick measuring/googling I realised that Shimano makes life hard for those who wants replace just a bearings. The problem is simple. Almost impossible to buy (decent quality) bearing in size 25x37x6mm, but it's broadly available bearing 6805-2RS (sometimes known as 6805-RD) which is 25x37x7mm. I've decided to buy set of ceramic bearings from China trough ebay, as I wasn't sure about result of the whole operation. They cost me £20 including postage so not too bad price after all for (semi)ceramic bearings. I've clicked "Pay" in PayPal and the fun begun.

Step 2: Dissassemble

Viva! Viva! La Revolución!

The cups are tricky to disassemble (actually stays "DO NOT DISASSEMBLE" on the cups). Shimano made the same size of hole inside cups as the internal diameter of bearings. So basically is a small gap (about 1mm) where you can actually attach bearing puller and disassemble it. Sounds almost impossible with standard bearing puller, so I came across with diy bearing puller made from cut washers, screw and other bits and pieces. Two washers on a screw and in between is another washer cut in a half. A sort of sandwich. The images shows only one piece slid.

So I've put the sandwich on the screw and inside move them aside so they catch the bearing and added a nut on top to keep everything compact. I must admit this is quite tricky to set it up, but once is done all you need is a vice or piece of tube as a spacer (or whatever suitable) and you can slowly pull bearing out turning the top nut.

After wrestling with diy puller for nearly an hour I had both disassembled. Pressing new bearings back was quickest and easiest part. I've put the bearings to freezer (old trick in order to use less force pressing them), and in the meantime cleaned cups, grease surfaces where new one will slide.

Step 3: Asemble

On the pictures you can see my "press" made of 8mm screw plus washers and some 19inch rack foot I've found at work, which apparently was exactly the same dimension as outer bearing race. Another hint. Instead of my "special rack foot" you can use socket 36mm from ratchet set. In fact is handy for any bearing as sockets in 1mm steps so is pretty easy to find right dimension. You need to remember that pressure needs to be applied on outer race of the bearing otherwise bearing might be damaged.

Step 4: Final Touch - Seal

Last bit is butchering slightly plastic washers. I've cut them by scissors and sanded down flanges as much as I could.
Made covers from 5.25 inch diskette (do you remember them?! ;-) ) you can see on the pictures. They're probably no necessary but I've decided to have additional protection at least against sand.
The final product you can see on the last image, and I assume if you attempting to do it there's no need explain how to screw them again to the frame ;-)
Good luck!



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    Does anyone know the size of the bearings for the SM BB-9000 (http://bike.shimano.com/content/sac-bike/en/home/r...


    I think it is not necessary to use special
    tools made by yourself, I managed to disassemble this cartrige with
    steel hammer and flat screwdriver as it was shown on this video:


    i found a actual same size 25x37x6mm ceramic bearing from china and waiting shipment only. in this case. do i still need to do your step 4 modify the seal or i can just direct used back the original seal after new bearing install ?

    do you think just replace the bearing ball to ceramic ball instead of replace the entire bearing ?

    what is the ball size ?

    1 reply

    I'm not sure what is the ball size. AFAIR was about 3mm? but I might be wrong. I'd say replacing just a balls will be quite tricky. I'd love to see if you can do it. The other thing is, I don't remember which direction the bearings are fitted you probably will need to remove them anyway. If I'll find old bearing I will ping a post with dimensions (google it?). Cheers


    Great write up - I've taken apart the bb to regrease the bearings (in spite of the Do Not Disassemble), but want to do a bearing replacement as well. Few questions:

    1. did the use of a 7mm bearing cause any problems? Did you just push the bearings in 1mm more, which left them with no gap ?

    2. did the ceramic bearings make a difference when riding or would you go back to regular steel ball/steel races?

    3. Why did you sand down the plastic washers - only because they became warped when you removed them or another reason?

    4. I don't have a rack foot (not even sure what that is), so I'd take your advice to use a socket to press in the bearing - any suggestion as to how to keep the socket centered?

    Thanks again.

    1 reply

    A1. No, not a problem with 1mm more on the spindle. I didn't push extra 1mm because it's simply impossible. Bearings are pushed to the end basically.
    A2. Hard to say if there's too much difference in performance. I'm not doing TT or stuff like that, that was simply an experiment. And at the end of a day, I still think I need legs rather than fancy equipment (and best area to shave weight is your body not a bike ;-)). What I can tell you is the whole drivetrain with approx equal push making exactly three spins of cranks (jokey wheels upgraded to TACX ceramic as well) in the same time new (~300km) Shimano 105 drivetrain is turning once. For the price I've paid for bearings I won't go back to standard bearings. Not only for the sake of performance but also because of durability.
    A3. At first of all, plastic washers have a small bulge on the inside (I din't explain that, sorry). That is designed for 6mm bearings so you need to sand it down in order to push spindle trough. Secondly I sanded down slightly the flange to make the whole BB as close to original dimension as possible (probably gained about 1mm) I don't think it's necessary but you need to experiment.
    A4. Rack foot is a standard foot for 19 inch rack systems ;-). Again my fault I didn't explained it too much. In order too keep socket cantered you need to centre the screw you're turning that's it. There is better/easier method where the required force is much lower. Simply put the bearings into freezer -25-30C for half an hour, and heat up cups with heat gun. Then you can literally push bearings with hands. You need to be quick thou ;-).
    Hope that'll help. If you have any questions ping me a message/comment.
    Keep'em rolling

    Nice instructable. I have a set of FSA Mega Exo cups that need new bearings. I may give this a try on those and see if the result is the same rather than putting in a whole new set of cups. It surely would end up cheaper than having to replace the full set of cups my cross bike so often.


    Great job! I took my Hollowtech cups to a bike shop to have the bearings removed, but the mechanic said he didn't have the tools to do it.

    I checked on the web and found out why. A press and the required adapter cost over $800! Which you functionally duplicated with a few shop scraps. I ended up getting new cups, but I like your solution better.

    The reason I had to change bearings is that my Boca ceramics self-destructed after only a few months use. The replacements have been going strong for 5 years.

    Q. What are you holding in your fingers in the first picture in Step 3?

    1 reply

    Hi. Thanks for comment. On third picture is the "puller". Two washers and between them another one cut in a half. But on that picture only one haf is shown. Hope that will explain a bit. Cheers

    I like that: "DO NOT DISASSEMBLE". Same as "NO USER PARTS INSIDE". Just makes the project more interesting.

    Have you checked for bearings at Boca Bearings (www.bocabearings.com)? I get my small ball bearings here, they also have ceramic bearings.

    Good job.

    1 reply

    Throw it, throw it, throw it, do not repair.
    Buy, buy, buy, don't think too much.
    Believe, believe, believe, don't ask.
    Be consumer not human.

    Woo! Good job, I came across this when doing a bit of research for my sheared rear axel. Nice post.