Cannondale eccentric BB
 

I have a new-to-me Cannondale tandem, probably vintage 2010 - disc brakes and 700c wheels. I'm trying to eliminate sync chain slack but I cannot figure out how to loosen the captain's bottom bracket. The 4mm bolt will back completely out, so I'm guessing the locking clip is AWOL. I've read posts here that all say to loosen the 4mm bolt and smack it with a mallet but that did absolutely nothing - it still won't budge.

Any other suggestions? It seems to me I should have to remove the cranks too - am I wrong about that?

Thanks in advance!

I made my own removal tool to draw out the wedge from the opposite side. Get a thin piece of flat steel bar (approximately 1/2in wide, 4 inches long). Get a shorter 4mm bolt.
Remove the crank arm on the opposite side you pulled the bolt out of so you can access the wedge. Put the steel piece across the bottom bracket shell over the wedge bolt hole. Thread in the bolt through the piece of steel (you may need to add some washers to take up some length). Then tighten the bolt against the steel piece to draw out the wedge.
I hope that makes sense.

I will get yelled at for telling you this, but here's how I handled the wedge: I backed out the bolt very little at first, put a centering tool in the bolt head to minimize any head damage, and tapped it with a 16oz hammer until it loosened. I wanted as many threads as possible taking the blow, hence barely backing it out. Yes, I knew the risks, but I also knew the wedge was appropriately greased, and that I hadn't torqued it/man-handled it when tightening it the last time. In your case...who knows the current state?

I eventually got tired of the C'dale wedge and replaced it with a Bushnell eccentric BB. With just my little hex wrench, I can adjust out on the road if necessary.

THIS! Don't bang on it with anything!!!!
There's a reason the eccentric has a hole in it opposite the bolt head side - to insert a shorter bolt into the barrel nut from the other side to extract the "stuck" wedge! It's almost like they designed it this way so no hammers would be needed! Wow!!!
A traditional Park cone wrench (short, two-sided) is the PERFECT "piece of steel" to use to extract the wedge. It's compact and can fit behind a crank arm and has a convenient little hole (two actually) in it to run the bolt through. I use this and a water bottle cage bolt with a washer or two and it works every time. No need for me to extract any crank arms (using traditional square taper arms on 122.5mm spindles) in my experience. YMMV.

I REALLY hate hearing the endless and repeated advice to "hit it with a hammer" when it comes to tandem wedge eccentrics. The LAST thing you want to be doing to your captain BB shell is be swinging a hammer at it! Sheesh! It's uncouth and shows very limited creativity when it comes to mechanical things. Some things can and should be hit with a hammer, but others shouldn't. And an eccentric wedge bolt is one that shouldn't be manhandled by ham-fisted people.

Please, no more advice to hit long, thin, "stuck" bolts with a hammer!!!

PS After you do extract it, be sure to apply liberal amounts of quality waterproof grease to everything in and around the eccentric when re-installing. Barrel nut, bolt threads, bolt head, BB shell, eccentric and wedge should be "dripping" with grease! Not really, but you can't use too much. The extra will squeeze out and you can re-use it anyway (assuming you properly cleaned everything prior to reassembly). I don't use anti-seize in mine, but you may wish to add it to your grease. And anti-seize alone is a bad choice - it's too "dry" and doesn't provide the needed lubrication for proper installation, future adjustment and removal, in my opinion.
PPS This has been discussed at length in the past. One reply or discussion even had detailed instructions on how to proceed with wedge removal the proper way. So do a search and you're bound to find it. Or perhaps it's on YouTube - or both!

PUT THE HAMMER DOWN! On Burely uses a similar type of "back out the bolt", and it worked great until one day it didn't and I couldn't figure out why until Mel from Tandems East pointed out that I had lost the outer ring nut that the eccentric wedge assembly pushed against. Have you done a search on the forum, its been discussed before, here's one with your same question.

https://www.bikeforums.net/tandem-cy...djustment.html

This is the way to go. I use a stack of 3 washers about an inch in diameter. I can do it without pulling the crank arm. Washers and bolt live in the saddlebag so I can address this on the road if need be. The wedge will come out. When it's time to put it back in, grease it thoroughly and don't tighten it too much. You'll be surprised how little torque it takes to hold the eccentric securely.