Carrefour
Heard an intermittent crack like a rifle shot - thought some kid had hit the frame with a catapult - on full power near top of hills. Obviously (with hind sight that is) one of the bearings got trapped. Started making a mild grating noise at times. Could not trace it. Thought is was the pedals. At about the 5000 km mark took bike to a shop in Tubingen in Germany - could not trace it. In another 1200 km my wife/stoker said she thought the pedal was getting loose. Was the whole crank shaft. So then we knew at last what it was. She could not pedal at all in the last 80 km into Amsterdam. BB totally collapsed. Replaced it with a new Truvativ bb ie same type. No housing damage - just lucky - or a new frame. The new bb has not collapsed. But now we have the shush shush noise (no cracking). Could not trace this noise which I suspect was there along with the bb noise so we could eventually not hear it. Thought it might now be the front bb. Replaced that - still there. Thought the new back bb may have been defective - put the original front bb on the back. Still there. So now I have just put in new bb on the back. We will test ride tomorrow. (the new Truvativ bb left cup had a defective thread so had to use the old front bb's). I suspect it is the rear hub - when heated expands and touches somewhere - it has a buckled wheel rhythm. Heard from the local bike shop manager that the Truvativ bottom bracket on his single mountain bike (which gets a hammering) does not last long he has been through three in a relatively short distance. So it seems the Truvativ bottom bracket is the Cannondale tandem's Achilles heel. Thanks for the Koolstop tip.