What is the deal with DA 7400 bottom brackets?

[auto_rock]

So I had a friend push his commuter into my shop the other day and he had a bag of parts he'd pulled off his other bike (the dude is a 6'6" monster, and had bent the other frame beyond repair). A mish-mash of old parts, including some DA-7400 cranks. First time I've ever fiddled around with old DA, and was reading the Sheldon Brown site, apparently they had an asymmetric bottom bracket.

1) Will a normal square taper shimano BB work? If it does will there be a slight difference in q factor for each foot?

2) Why did they do it this way?

[Secosera]

I use a FSA square taper ti BB with my 7400 crank and it works fine. I don't know about the Q factor though. It feels fine when I ride that particular bike.

[rustychisel]

hmmm, dunno for sure.

I have DA 7402 cranks on a fixed gear, chainring on outer position, and a symmetrical Shimano BB and it works fine. Never thought about it much.

[oldpotatoe]

So I had a friend push his commuter into my shop the other day and he had a bag of parts he'd pulled off his other bike (the dude is a 6'6" monster, and had bent the other frame beyond repair). A mish-mash of old parts, including some DA-7400 cranks. First time I've ever fiddled around with old DA, and was reading the Sheldon Brown site, apparently they had an asymmetric bottom bracket.

1) Will a normal square taper shimano BB work? If it does will there be a slight difference in q factor for each foot?

2) Why did they do it this way?

113mm for english threads or 115mm for Italiano threads...any current or past BB, including shimano and Sugino. JIS taper. I have installed many UN-72 type on these DA cranks..samo for shimano 600 of the same era.

[auto_rock]

Thanks, Old Potatoe.

So I am still wondering why it was ever done differently for DA 7400.

Was it just to "prevent" interchanging parts?

[oldpotatoe]

Thanks, Old Potatoe.

So I am still wondering why it was ever done differently for DA 7400.

Was it just to "prevent" interchanging parts?

Who knows. shimano has tried to institute 'standards' for years, like octalink for example. All of DA 7s/8s, 7400 series, was unique, like the RD, not compatible with '600' shifters and the like, the 7s uniglide and 8s hyperglide freehub body and how it bolted to the hub, etc.

[auto_rock]

Huh, just like the tall splines on early 10-speed.

Silly Shimano.