Bicycle Mechanics - Aluminum frame repair?

The moron who sold me my all-aluminum-frame Cannondale 400 didn't have the stops adjusted on the rear derailleur. This moron, who rode the bike without checking it on the stand first, stuck the derailleur into the spokes, tore the derailleur apart, and snapped the aluminum derailleur mounting tab off of the dropout! Fortunately, the bike kept rolling and I wasn't in traffic. Lesson learned: CHECK THE BIKE BEFORE RIDING IT!

Questions are these:

1. Is it feasible to epoxy the bottom half of the derailleur mounting tab back onto the frame, chase the threads with a tap, and go to riding again?

2. Is it feasible to use a steel "derailleur mounting plate" after grinding off the remains of the existing tab? This would, obviously, move the rear of the chainline outboard by about 1/8", but it shouldn't matter that much. The bigger problem I see is that the steel mounting plate requires both a small "anchor" bolt and a bolt-on-axle sized wheel axle to keep it from shifting. Perhaps I could weld, glue, or rivit on the plate?

3. Is it feasible to TIG or MIG weld the remains of the existing aluminum tab back onto the bike and then recut the threads?

4. I understand Cannondale has a "trade up" program. Would this bike qualify in the shape it is in?

Thanks.

The moron who sold me my all-aluminum-frame Cannondale 400 didn't have the stops adjusted on the rear derailleur. This moron, who rode the bike without checking it on the stand first, stuck the derailleur into the spokes, tore the derailleur apart, and snapped the aluminum derailleur mounting tab off of the dropout! Fortunately, the bike kept rolling and I wasn't in traffic. Lesson learned: CHECK THE BIKE BEFORE RIDING IT!

Questions are these:

1. Is it feasible to epoxy the bottom half of the derailleur mounting tab back onto the frame, chase the threads with a tap, and go to riding again?

2. Is it feasible to use a steel "derailleur mounting plate" after grinding off the remains of the existing tab? This would, obviously, move the rear of the chainline outboard by about 1/8", but it shouldn't matter that much. The bigger problem I see is that the steel mounting plate requires both a small "anchor" bolt and a bolt-on-axle sized wheel axle to keep it from shifting. Perhaps I could weld, glue, or rivit on the plate?

3. Is it feasible to TIG or MIG weld the remains of the existing aluminum tab back onto the bike and then recut the threads?

4. I understand Cannondale has a "trade up" program. Would this bike qualify in the shape it is in?

Thanks. Cut your losses and go for # 4, or make it a beater single speed. Cdales trade deal is good even on kids trikes from a dumpster. Some dealers don't even require a frame. Some will try and stick you up for a good Cdale frame they can resell and make a $$.

Yeah, cut your losses and ditch the frame.

I'm not sure if you can even weld steel to aluminum.

If you do weld on the frame, it will lose its T6 temper (At least, that's what my Cannondale is). The Heat Affected Zone (HAZ) from welding may extend into the rear dropout. Now the side you welded is (maybe) T0 and the other is T6. Sounds bad to me.

Did you just buy it?? From an LBS? If so I would take it back and RAISE HELL. If not, you are possibly screwed.

Here is another idea. Without seeing it, I don't know how feasable it is. Some bikes have replaceable hangers. You could get one of those and maybe, just maybe, you could get whats left machined to use the new hanger. It might cost too much though.

Depending on the hub spacing you can get a new rear derailleur from Shimano. The Saint or Hone bolts onto the axle of the wheel. This would mean no more QR and the hub spacing will have to be either 135 or 150mm. They are spendy too.

Did you just buy it?? From an LBS? If so I would take it back and RAISE HELL. If not, you are possibly screwed.

Unfortunately, I bought the bike from a pawnbroker on e-Bay. I have only myself to blame for not checking before riding - I know better. Unfortunately, enthusiasm got the better of me...

I'll look into repair options. Conversion to a track isn't feasible with aluminum - the alloy doesn't take well to cold-setting like steels do.

I've seen "bolt-on" derailleur hanger plates on steel frames. I'll look for one of those on a garage sale bike.

Thanks for the reply!

Cannondale road frames made after 1991 have a replacable derailluer hanger that is the bottom half of the dropout. I don't know if the "400" you have a road bike.

There is a letter prefix to the model number 400, I'm pretty sure. This would allow better help as we would know better what bike we are dealing with..

Our only Cannondale, a 2003 MT800 tandem, has a replaceable derailer hanger and I suspect most all of their frames do if made in the last several years. Our frame is blue and the hanger is black.

Otherwise, I would think getting another frame and stripping the components would be an alternative to the trade up program.

Good luck,
Doc

My 'dale MTB (from the 80's) has a replaceable hanger, so I'm sure that your newer frame has one too. Any Cannondale dealer should be able to get one for you- they might even keep them in stock.

If it isn't a replaceabel hanger. Try JB Weld. It's worth a shot. That stuff is amazing. If you can get the part cleaned and clamped in place JB Weld will hold it.

I have some pictures of an axle I made for a bike trailer. It is a hollow qr axle glued into a piece of 3/8" u channel aluminum. It the first picture I have twisted it to show the strength. The second one is a close-up.

You can see the JB Weld inside the u channel holding the axle in place, I have had several hundred pounds on this axle with no signs of fatigue.

Epoxy and things like JB Weld usually won't work for a butt joint, which is what you would have for a tab that snapped off.

It is fine for sleeve joint like that axle in a channel, but for face to face stuff not worth it.

This 400 was NOT made with a replacable hanger - just flat aluminum plate with the hanger below. What I **did** find out at the LBS, though, was that the existing plate can be filed away, drilled, and tapped to accept the replacable hanger! The LBS even had a hanger in stock. Now all I need to do is get out the file and go to work. Happy, happy!

My 'dale MTB (from the 80's) has a replaceable hanger, so I'm sure that your newer frame has one too. Any Cannondale dealer should be able to get one for you- they might even keep them in stock.
Most Cannondale hangers can be bought from any LBS. Wheels Manufacuring makes aftermarket replacments that are available in one bike shop suppliers catalouge that I have at work.

For anyone interested, there's a website devoted to derailleur hangers (http://derailleurhanger.com/index.htm). When I return to the US, I will be donating some obscure ones I have floating around.

If it was an LBS that you purchased it from, then do what others have suggested, take it back for a replacement or refund. But, if the purchase wasn't from an LBS then I see two morons in the picture.

Um, he's already admitted that at the start of this thread, no need to rub it in.

One moron sells the bike, one moron messes up the bike, one moron calls a second moron a moron after the third moron doesn't read the second moron refer to himself as a moron.

Q: Who's the BIGGEST moron?

:D

Uh, George W?