Bicycle Mechanics - 68 x 117.5 Bottom Bracket Help.

I removed the 13 year old bottom bracket from my Schwinn last night and it was pretty nasty inside. I don't want to rebuild the thing, I just want to replace it with a newer cartridge bottom bracket, but I'm not sure what kind I need.

The old BB has the following markings on it:

Shimano
68 = T = 117.5
D-3A LG

I'm assuming that 117.5 is the spindle length. A web search of 68 x 117.5 turns up very little. My question is, can I just use a Shimano UN-73 BB with 68 x 115 measurements? Will that 2.5 mm difference really mess up shifting or anything? Performance has the UN-73 on sale for $20. Any help would be greatly appreciated. Thanks!

- Matt

All Those numbers/letters on there means something(axle end factors, tapers, etc...), and a shop with a Sutherlands Manual will be able to tell you what they mean and match you to a current BB that will closely match the BB you have now. If you just want to try the Performance BB, it should be pretty close. 117.5 is a BB axle length. Performance does have a very helpful technical dept that you can ask to be transfered to when you call in. They may be able to help you.

The Performance BB should work. It will shift your chain line in by the difference in length assuming Shimano has not changed the taper, which is highly unlikely. (There are several different taper specs Euro vs east asian.)
This will require readjusting the front derailler limit screws and reclampling the cable to the new length. Rarely there will be insufficent clearance between the
inner chain ring on triples and the chain stay with shorter BB. Steve

Shimano has a 68x118 BB

It will shift your chain line in by the difference in length

1/2 the difference in length? :confused:

If so 1.25mm shouldn't be a problem and most of that you can loose in the lateral positioning of the BB?

Originally posted by cowdotpat


If so 1.25mm shouldn't be a problem and most of that you can loose in the lateral positioning of the BB? There is no lateral positioning of the BB unless you use a shim or have one with adjustable chainline.

Cowdot: Most BB are assymmetric with the difference in length
on the R (drive) side only. This is especially true with splined but was true with tapers also. Triples do tend to have some of the longer length on the L but most will be on the R. One of the nice things about Phil Wood BB was the ability to adjust the side to side placement of the BB by a few mm. Steve

Thanks for that, it clears a few things up for me. I didn't realise BBs were asymmetrical. I had my eye on a Phil Wood and it was there that I read about lateral adjustment without realising it was a special feature of his kit. As I wrote my last post I thought I was missing something since there was no adjustment in any BB I've fitted.

Still I'm here to learn