Swapping Double for Triple
 

I've gotten a lot of good advice regarding my recently acquired Motobecane Inter Club tandem. I now know that I have TA cranks and have ordered the special puller in order to service the bottom brackets. Since I plan to pull the cranks, I'm wondering what would be involved in installing a triple crank in place of the current double.

Assuming you tandem has TA Cyclotouriste cranks, you'll need a new six chainring bolt kit for the triple (TA ref 86). They've got longer sleeve bolts and extra spacers for the third ring.

Of course, our good friends at pb*bikes eBay have it at about 5 times its normal value. I've seen them pop up on the 'bay for around $25, like this set that ended a few months ago.

Have you checked to see if your BB spindle is long enough for a triple? The triple will require about 6mm more room than a double, possibly requiring a longer BB spindle.

I'm not sure about the spindle length, but that's exactly the kind of advice I need before I get in over my head. Thanks.

With a little luck, someone with specific knowledge of just which spindle is required for that TA crank will chime in eventually. But in general, if you add 6 mm to the drive-side length of an existing double spindle, you'll end up with the right length for a triple. Remove the existing spindle, measure it, and take it from there. If there's a good bike co-op near you, see if they have a box of used spindles you can root through. Assuming that you'll be re-using the original bottom bracket, make sure that the distance between the "ridges" of the new triple spindle matches that of the double spindle.

Here are some excerpts from TA catalogs showing the bottom bracket spindles:

http://www.os2.dhs.org/~john/ta-spindles.jpg
http://www.sheldonbrown.com/harris/i...a-bb-axles.gif

From this I gather the original spindle should be a TA 344 and the desired replacement a TA 374. What complicates this a bit is that both are available in two different overall lengths, differing on the non-drive side (NDS) part. That is not normally an issue however this is a tandem with NDS sync/timing rings, so you'd probably want to match the existing 17mm or 19mm dimension there. I'd guess that the existing spindle measures 19mm NDS so I don't think it will be an issue since all of the TA 374 spindles I've seen are the 123.5mm overall versions with the 19mm NDS length, like this one: T A 374 Bottom Bracket Spindle 123mm for Triple Crank | eBay

Note one of those charts has an even longer "Tandem" TA 375 spindle, but I believe that was for the tandem crankset version TA offered with the sync/timing rings on the drive-side.

Do you know the current spindle size? I spent a looooong time looking for a TA triple spindle for our tandem, ended up not using the TA anyway. Sutherlands lists as something like 127mm or maybe I misremember. Pull your cranks off the spindle, measure its length (not counting protruding threads if it is nutted instead of bolted), and also see if it has a size code like 3N or 5S or something, then check Sheldon Brown or Sutherland for the meaning of those codes. I may have a TA spindle that will work for you. But maybe not.