Confused - My 1980 Shimano ISO Sq Taper is bigger than JIS..

mightymidget Posts: 74
edited July 2010 in Workshop
Hi all,

I'm a little confused. Please help..

I have a old Shimano BB dated 1980, think it might be a BB-7500 as it came with some NOS Dura-Ace FC-7200's cranks (Dyna Drive dated 1980) that I recently purchased.

Apparently Shimano used to recommend and sell them with the BB-7500 bottom brackets in widths of 107 and 109mm (but mines 112mm). This got me thinking it might be a GB-100 but the date codes doesn't correspond as the GB-100 stopped production in the late 70's.

Anyhow, regardless of the BB model It appears to be of an old Shimano ISO type before they went to JIS tapers. What's confusing is that the square tapers on the BB appears to be bigger than JIS BB square tapers.

This doesn't make sense as King Sheldon Brown clearly states on his site that ISO tapers are smaller than JIS tapers. But he seems to be making a comparison between the newer Campag ISO vs JIS.

So, does anyone know if the older Shimano ISO BB tapers are bigger than the newer ISO standard adopted by Campag and Euro manufactures and more importantly bigger than the JIS. And if not how come my 1980 Shimano BB is bigger (fatter) than the newer JIS standard tapers.

Unfortunately I don’t have a Campag ISO BB to compare but I've compared my Shimano ISO to 2 JIS bottom brackets and in both cases the old ISO tapers are fatter than JIS..

Sheldon can't be wrong so please can anyone advise..

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