Broken FD braze-on advice

A buddy of mine (if you need some paint work Brooks Airbrush Studio) was needing a tri bike to use, and mine was collecting dust. I had just picked up an Ultegra SL FD to match the rear from a forum member, I wanted to change it out before I turned it over to him. So while taking the old one off it basically dropped in my hands. Glad it happened while no one was riding. It's a Guru Cron Alu, aluminum teardrop seat tube that I bought second hand.

I have access to a Miller Econo tig, an XL 350 mig with the aluminum set-up. I also have a couple gallons of West systems epoxy, with an assortment of carbon, fiberglass, kevlar cloth, and tow. Any advice or should it live out it's life with a 1x10 drivetrain.

Tim

http://farm9.staticflickr.com/8337/8...d2b6bf_b_d.jpg

Broken FD - a set on Flickr

I vote 1x10 with a wide range cluster in back.

Try to find a front deraileur that clamps below it, if not, 1x10.

I have used metal epoxy to fix various brackets in the past. You can file the old weld off as well and use a clamp on FD. I wouldn't gring it as too much heat will ruin the heat treatment of the aluminum. I haven't used this but plan to in the near future: Aluminum Repair Video using our brazing rod HTS-2000 and a heat source, no welding machine needed!

Broken FD reminds me of the Mitch Hedburg bit about broken escalators :)

Good luck with the repair!

Presumably a replacement rivet on tab would work. Not sure on the size/ shape of the pear tube nor the wall thickness.

Something akin to this:
http://www.cycle-frames.com/bicycle-..._FD_RVT-06.jpg

I guess I should have read that the tube wasnt round.....

Quote:

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Originally Posted by Eric Estlund

Presumably a replacement rivet on tab would work. Not sure on the size/ shape of the pear tube nor the wall thickness.

Something akin to this:

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I am in no way an experienced frame builder but I can maybe chime in with this one as I've worked with many carbon frames in the past.

Many big name manufacturers (Trek, Spec, Cervelo ETC.) uses a similar set up on their aero shaped carbon frames.

While rivets alone are more than strong enough to hold the FDM in place, these have tendency to pull out or break over time as the FDM rocks back and forth with the working of FD.

In order to prevent this, most companies use epoxy to glue the FDM in place. Keep in mind that epoxy is in place mostly to fill the gap underneath the FDM to prevent the FDM from moving about.

Bond strength in the area is not critical, in fact, many companies chose to glue over paint for cleaner look. (5 minute epoxy works just fine)

One important thing is to use steel rivets as aluminum ones generally do not stand up to the force that are being put on them and break.

Just cut off the existing FDM, file down the weld and pop on the new one and voila!

Cheers!


(Edit : I would not worry about the rivets pulling out of the wall as long as you drill the proper sized hole for the rivet. This is more of a problem with carbon frames where there are only 3-4 layers of carbon on the ST. Your Aluminum frame with .8-1mm thick wall would be no problem at all)