I recently removed the Shimano Square Taper bottom bracket from my Trek 950 Single Track with the idea I would overhaul and reinstall it.

While removing the unit I noticed the two rubber dust seals (or grommets) were different sizes. The side of the BB that had the smaller, ill fitting seal was dirty and that side of the spindle was pitted compared to the side that had the correct size seal.

I've owned the bike since new, and had never touched the BB prior to this. I have no idea how two sized seals could have been installed... just doesn't make sense.

Now, I want to reinstall the BB but can't find a replacement seal that is correctly sized (see measurements below), any ideas where I can find a replacement? I've checked numerous grommet/seal mfrs and no one seems to have something remotely close to the following sizes; any help is appreciated:

A-Bore: 16.3 mm
B-Groove Width: 4.5mm
C-Groove Dia: 18.3mm
D-OD: 21mm
E-Thickness: 5mm

Do you know anyone who owns a lathe? Can you tell what material is it made from?

did you ask shimano? maybe get a replacement BB if this one was assembled wrong or at least get the proper sized seal.

I assume the bottom bracket isn't a real Shimano part since Trek (and most other makers) tend to use lower cost, no name components in areas where the part is hidden. Therefore, finding an suitable OEM replacement isn't likely.

However, have you considered replacing it with a sealed cartridge bottom bracket. These are low cost, durable and require zero mainrenance.

How old is the bike? IIRC, Trek started having their Singletrack line welded in Taiwan (instead of brazed in Wisconsin) in the mid nineties (1994?). I have seen some weird things on their Taiwanese assembled bikes - like pre-patched inner tubes and stuff.

Have you considered switching to a cartidge bottom bracket? THey are cheap and long lasting and available in most sizes.

My 1994 Trek 920 was made here.

Zombie thread. The post above yours was made over 3 years ago. I expect the OP has gotten his bottom bracket problem solved by now.

I posted it just in case someone searching came upon this and had a 1994 Trek. I didn't want them to have the wrong info.

no such thing as a zombie thread

There was since you didn't add anything useful RE Bottom Brackets.

But it is useful to someone who has a 1994 trek and thinks it was foreign made. Your's and Hillrider's posts were not adding anything useful.

Some people need to knock off their useless comments.

Better look in the mirror!

Un screw whats there, look for a replacement, install it .. the British BB thread standard remains Common.

Thread closed.