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BB length for Dura Ace 7400 cranks, 8 speed

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BB length for Dura Ace 7400 cranks, 8 speed

Old 11-26-20, 10:42 PM
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klasse
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BB length for Dura Ace 7400 cranks, 8 speed

Wondering if anyone is running 8sp brifters with Dura Ace 7400 cranks. So, here's my experience:

Sheldon Brown says it should be 113mm with +3mm offset (3mm longer) on the drive side. I ordered a Phil Wood bracket to this spec. I could not get it to work with 7400 cranks, 8 speed. So, I just decided to go with Shim 600 tricolor cranks, 113mm symmetrical. Phil was kind enough to move the bearings over for me, no charge!

My sister's bike, 7sp friction shifters, has DA 7400 cranks with a Phil 112mm bracket, some offset on the drive side. Works beautifully.

Just wondering if someone out there has some insight, experience running 7400 with 8sp. What size bracket are you using? thanks
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Old 11-27-20, 12:58 AM
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Originally Posted by klasse View Post
Wondering if anyone is running 8sp brifters with Dura Ace 7400 cranks. So, here's my experience:

Sheldon Brown says it should be 113mm with +3mm offset (3mm longer) on the drive side. I ordered a Phil Wood bracket to this spec. I could not get it to work with 7400 cranks, 8 speed. So, I just decided to go with Shim 600 tricolor cranks, 113mm symmetrical. Phil was kind enough to move the bearings over for me, no charge!

My sister's bike, 7sp friction shifters, has DA 7400 cranks with a Phil 112mm bracket, some offset on the drive side. Works beautifully.

Just wondering if someone out there has some insight, experience running 7400 with 8sp. What size bracket are you using? thanks
So the obvious question is why not just buy the matching DA 7400 BB off of ebay? Also, do you have 7400 or 7410 crankset? 7400 BB has 112 spindle but the 7410 uses 103 as the 7410 crankset is most definitely not compatible with the ultegra BB from the same year.
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Old 11-27-20, 08:24 AM
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7400 English = 112mm, Italian = 113mm. I've ridden 7400 cranks with both and as 7speed (downtube) and 8 speed (7400 STI). I used the DA bottom brackets, not Phil. Never had any chainline issues.
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Old 11-27-20, 08:02 PM
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Are you running a double or triple and what gear range it will make up to 6mm difference in ideal BB length on this crank ranging from 110-116". Yet I would think for the front less than ideal it should run fine on the front. Have you tried running a 1 or 2mm spacer on the drive side which is often needed when using a different brand BB on a crank?
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Old 11-27-20, 08:17 PM
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And what era is the other 112 mm Phil unit...
Way back they made at least 4 permutations.
AND
There were different outboard tip dimensions...

the Mod Phil may not set the arm far enough in or have too much engagement.

most are 2 degree in taper but that is just the start.
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Old 11-28-20, 06:05 AM
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I have both the 7400 and 6400 on hand (and could find them), so I measured them for you, I hope it's of some use.

BB-7400 Italian 113mm, 2mm longer on the drive side

BB-6400 Italian 115mm, symmetrical. The 113mm BB-6400 is British threaded, and I don't have one on hand to measure.

I think the implication is that, using the same FC-7402 crankset, the drive side would be in the same position with either BB, and with the BB-6400 the non drive side would be 2mm outboard of the designed position.

Last edited by Seanaus; 11-28-20 at 06:14 AM. Reason: More detail.
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Old 11-28-20, 03:01 PM
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Lots of questions: Was using double ring, 7400 cranks (the shiny ones) on a Bridgestone RB-1. Ultimately, as mentioned above, I just switched to the Shimano 600 cranks using 113mm symmetrical and all is gravy.

My sister's bike is the same year/model, using an old school PW 112mm bracket with some offset on the drive side, works great with her 7sp, DA 7400 (double) cranks.

I'm guessing that I needed a longer spindle, longer than the 113 (+3 offset on drive side) I was trying to use! Thanks for the responses.
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Old 11-28-20, 04:06 PM
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I reference this with some frequency.
https://www.sheldonbrown.com/bbsize.html
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Old 11-28-20, 04:39 PM
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I'm curious what dimension didn't work using the "offset" Phill 113mm bb?

Did the chainring(s) contact the right chainstay?

Did the front derailer run out of travel in one direction or the other?


I was always troubled by the terms "offset" or "+Xmm" when describing spindles, because this is subject to imterpretation.

For example, offsetting a symmetric bb spindle 3mm makes the right end protrude 6mm further than the left end.

And saying "113 +3mm", does this mean that the spindle is 113mm symmetrical with an extra 3mm added to the right end for a total of 116mm?
Or does this mean a symmetrical 113mm bb that is then moved 3mm over toward the right?
Or does this possibly mean that the symmetrical 113mm spindle is actually moved over 1.5mm to make the right end protrude only 3mm further than the left end?

I have always measured and labeled bb's and spindles by measuring how much further that the right end protrudes than the left end, dividing this by two and calling the result the offset.
So, a 119mm spindle that is actually offset 1mm is described as such!
Like this broken one:


Thus the "offset" term refers to the cup spacer thickness I would use to similarly offset a symmetric 119mm spindle.

Last edited by dddd; 11-28-20 at 06:15 PM.
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