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

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..

Thanks,,

maybe put a micrometer/vernier onto the early axle you have and see how it compares to the "later " 7400 axle ? I thought shimano were always JIS from reading Sheldon Brown.

latman":32hbd7mc said:

I thought shimano were always JIS from reading Sheldon Brown.

Click to expand...

Um, I always thought that they used ISO square taper up to about 1981/82 then swithched to the new Japan Idustry Standard. Certainly looking on velobase ( http://velobase.com/ViewSingleComponent.aspx?ID=2338c300-aa3c-4d07-9e85-98ebc6c74ac3 ) it shows all the early shimano stuff as ISO square and a transistion to JIS in the early 80's.

As for the BB-7500, as far as I know it was really a track fitting (NJS standard) see here http://velobase.com/ViewSingleCompo...4505-4401-85B1-FFADA5DBF76A&Enum=119&AbsPos=7 which was ISO standard. Sheldon lists these NJS components as the same as Campag ISO. But I have my doubts as that would make them slimmer not fatter than JIS.

This is my problem, there seems to be no information about the size of the early shimano ISO square taper. At the moment I starting to think that they must be a different size to the ISO size campag and european manufactures have adopted.

Certainly the BB I have is Shimano, is 1980, and fatter than the newer Shimano JIS. Where as the Campag ISO, from what Sheldon quotes, is smaller than JIS.

As of yet I can't confirm the model of BB I have. Possible BB-7500 or maybe a GB-100 early Dura-Ace.

Still very confused..

Yep , it is ISO ,at least you have the BB you need

Ignoring the axle, what's the shell ?
English (Their default), Italian or French ?

and back to the axle, what's stamped on it ?

IOfmega - > Zeus -> ISO -> Campy - >JIS read out from Sutherland's 6th Edition on the tendencies from smallest to largest end sizes.

JIS standard is 12.65mm (tolerances unknown ?)

Only defined one is ISO
12.6mm +0.02 - 0.05 across flat 1.5mm from end


Also form same book in it's many lists
BB-7300 (7500 AX) = JIS (closest size)
BB-7600/7400 Campy (closest size)

BB-7200 came in 112mm length (ISO) and '68 W 111' on the axle (classed under 'old-double')

BB-7400 came in 112mm length (Campy) and should have '68 W 112' or '68-W' markings on the axle

Thanks for your detailed reply, which unfortunately confirms my confusion as it contradicts what I'm seeing.

FluffyChicken":2coo7wjd said:

IOfmega - > Zeus -> ISO -> Campy - >JIS read out from Sutherland's 6th Edition on the tendencies from smallest to largest end sizes.

Click to expand...

This is what confuses me, from the above that would suggest that if it's ISO then it should be smaller than a JIS BB, but it's not. When I put one of my newer DuraAce FC-7410 JIS crank arms on it and then put the same crank on a JIS BB then is goes on further by 2mm on the JIS BB. On the Old ISO Shimano BB the crank arm sticks out 2mm more in comparison. Therefore the ISO BB must be bigger as the crank doesn't go on it as far. It doesn't tally with what is written in book and on the web :?: This is why I question if the older Shimano ISO is in fact the fattest BB.

FluffyChicken":2coo7wjd said:

Ignoring the axle, what's the shell ?
English (Their default), Italian or French ?

and back to the axle, what's stamped on it ?

Click to expand...

Well, the shell is 68mm, French 35xP1, Axel 68=w=112. Date code is FL which is 1981/Dec.

FluffyChicken":2coo7wjd said:

BB-7200 came in 112mm length (ISO) and '68 W 111' on the axle (classed under 'old-double')

Click to expand...

Could be this but has 68=w=112 on the axle.

FluffyChicken":2coo7wjd said:

BB-7400 came in 112mm length (Campy) and should have '68 W 112' or '68-W' markings on the axle

Click to expand...

BB-7400 was 1985..( http://velobase.com/ViewSingleCompo...C7B4-4B22-B6DE-821D7D7B7B97&Enum=119&AbsPos=8 ) Can't be that, it's too new.

Ultimately I'd like to get a sealed cartridge BB to replace this odd cup and cone, something nice like a Royce or Phil wood. But at the moment I can't order anything as I'm unsure what to ask for. If I order ISO I'll get something that resembles Campags ISO tapers, which from the above would be way too small...:?:

Here's a few pics of the little blighter:

Links to photobucket:

http://i476.photobucket.com/albums/rr128/thehotone25/Shimano BB/attachment-4BNBGV.jpg

http://i476.photobucket.com/albums/rr128/thehotone25/Shimano BB/attachment-0LG3FV.jpg

http://i476.photobucket.com/albums/rr128/thehotone25/Shimano BB/attachment-M7G5FV.jpg

http://i476.photobucket.com/albums/rr128/thehotone25/Shimano BB/attachment-IJA4FV.jpg

After trying different cranks and BBs, I get the idea that manufacturers in the past largely use their own taper standards, even one manufacturer might have more than one taper size and shape.

Eg, Stronglight 49D is really small, the crank hardly goes onto a 1980s Campagnolo axle, although it is a very old model of cranks so Stronglight might have kept with an outdated taper to maintain compatibility with existing cranks and BBs.

I once tried a Omas cartridge BB (Italian co, maybe 90s) with a Campag NR crank but it wasn't a good fit, the crank didn't go on far enough.

I think it's only relatively recently that tapers have reduced to 2 standards. Also, different tapers in the past was not really a problem, cranks always came with its own model of BB. Spare BBs were sold by model and number of rings, whereas nowadays people seem to mix and match cranks and BBs and just spec an axle length.

...B-7200 came in 112mm length (ISO) and '68 W 111' on the axle (classed under 'old-double')...
Could be this but has 68=w=112 on the axle.

My bad a typo, 112 not 111

I happen to have the 1982 catalogue in picture format.

Talking of bottom brackets.
Shimano where using what is now Octalink back then as well, not just the splines

If you want to go nutty with tapers look here
http://www.icelord.net/bike/sutherland.pdf
(big download but well worth it)