Sjtaylor

I’ve got the rear wheel off of the new to me 1984 720. It’s a seven speed with a bent axle. I’m headed to my LBS for the right freewheel removal tool and possibly a replacement axle. I hope the bearing races are okay as I’d like to finish the rebuild and put some miles on this bike. I think I hear bearing noise so a bit concerned about what I’ll find.

id like this to be a temporary fix and come up with a permanent/stronger rear wheel setup. I’ve been reading and learned that a cassette hub replacement with a modern nine speed cassette would require a crank change so the thinner chain wouldn’t fall between the chain rings. Things suddenly get more interesting. I guess my first thought is to find a modern solution that wouldn’t require cold setting the dropouts wider and keeping the period correct 48/44/28 setup. I’m willing to invest some $$ in the solution. Any suggestions?

i have a 2013 Trek 520 that will be replaced by the 720. Would it be crazy to make the 520 a donor for the 720? I just now thought of this. If I bought a quill stem adaptor I think I could just swap parts. Save the original components and I could always go back.

What have others done? Thanks.

canopus 

Is it the helicomatic hub you have?

Don't assume you will have problems. Just be aware you could have these issues.
You don't need to cold set these frames for 130 hubs. If you want to be a stickler and have a way to control the frame bend then by all means but it isn't necessary. Between my Treks and Canondales, I only align them and shove my 130 Campy's in with my compact double cranks. If you want a 9 speed cassette, then get one. Don't worry about the crank/chain to much. Although the possibility exists that the chain could slip, it likely won't. It isn't like you're racing this particular bike, right?, I think for those few times it might slip it is easy enough to work it with the shifter while pedaling and you can always get a crank later if needed. If you want to keep the traditional 1/2 step setup then keep track of your gears and make sure the changes work for it whatever you do (cassette hub or freewheel). If not, Boulder Bicycles got in some IRD 30/46 cranks that I would love to have for a 10s/11s setup.

Bill Kapaun

While experimenting with different length cranks, I installed an old cottered crank from an early 70's 2X5 speed.
No issues with the chain dropping between the rings, with my 9 speed chain & cogs.
This was a friction shifter at the time, so I can't comment how well it would have indexed, especially since I normally use a triple.
Don't make it a problem unless IT makes it a problem.

Sjtaylor

I got the removal tool and removed the cluster from the hub using the tool in a vise. Worked great. I removed the bent axle, chucked the axle in a drill press and sure enough the bent axle was cracked. It snapped off in my hand. I also got a new replacement axle so lm good there. When I was cleaning up the hub I noticed a crack in the flange. I guess I can complete the axle installation and try the bike out. Still thinking about where to go with this.

Turns out the hubs are Shimano Dura-Ace First Gen High Flange 36 hole hubs. It looks like I can purchase a replacement hub but I’ve still got the broken axle worry with my weight on a loaded tour. I’m still researching.

WizardOfBoz

A crack in a hub flange is generally not something you want to ride on. Especially if you're using this as a touring bike with rack and panniers. Picture of crack might help but my default advice is to find a new (or vintage on ebay) 36t hole hub suitable for your cluster, Alternately, sometimes a new wheel is cheaper than relacing a new hub into the rim.

If it were me, I'd try to find the same hub on ebay, in good condition.

Sjtaylor

I found a replacement hub on EBay. The crack in my hub is through a spoke hole so a spoke will let go at worst I think. I have the wheel hub greased, reassembled and back in the dropouts. I have a longer stem, replacement brake hoods and new bar tape to go on before the first ride.

Still on the fence about the EBay hub. For now I’m happy to check out the ride.

icemilkcoffee 

Assuming you have 126mm rear spacing. You can use a Shimano 7 speed cassette hub with 126mm spacing. With the 7 speed cassette hub you can run 8, 9 or 10 speed cassettes- you just have to leave out one cog (effectively turning them into 7,8 or 9 speeds).
I favor the 10 speed drivetrains because they come with the Hollowtech II cranksets and external bearing bottom bracket- light and strong and easy to maintain. The other advantage is that you can get compact cranksets for it.