jadocs

You guys ever seen something like this?

Was in the process of starting a sprint and the front derailleur adapter just snapped in half. (less than 4 months old).

This is a Dura Ace FD-R9150 SM-AD91-L adapter (34.9mm). I was already in the big ring (no front shift) and had just shifted the rear before stomping on it. I ended up ordering a replacement off Amazon and sent Shimano a message to see what they have to say.

Litespud

thehammerdog

Racing Dan

Or it was installed with too much torque.

jadocs

Yeah, I've been searching and haven't found much info. I can't speak to torque as it came assembled from the manufacturer. I think it does look like pot metal, like Litespud mentioned. I only put out 817 watts before it snapped. I can only imagine it being some kind of defect.

jadocs

Well, Shimano said they would warrantee it, but I would have to bring the bike to an authorized dealer and have them look it over, order the part and install it.

Steve B.

Titanium bike with cast aluminum clamp using a steel bolt ?.

The aluminum gives first when over tightened, so likely at whomever assembled.

I can't say I've ever read of this.

jadocs

I agree Steve, I wish I could say that it was overtightened, but can't. I do know both bolts have the same torque specifications 6-7nm.....and the bolt that secured the derailleur to the adapter did not feel overtightened when I took it off.

nomadmax 

I've never seen a FD clamp break but I'd take that all day long over a crushed seat tube on my titanium bike

jadocs

Yep.... Thankfully everything else appears to be fine. As soon as I heard it pop (loud), I knew I broke something and coasted to the side of the road.

jadocs

New adapter clamp is installed. I know the torque is spot on as I did it myself. Will see if this was just a fluke occurrence.

Lemond1985

Maybe it was already broken from a previous front shift made under heavy torque, and was just barely hanging together. The rear shift was enough to knock it loose.

That's a possibility I suppose.

JohnDThompson 

+1 this.

We had a rash of this type of failure with Huret Jubilee front derailleurs at Trek.

jadocs

I could see that being a possibility, but the sound was impressive. Guy that I was chasing heard it and thought someone crashed, that's how loud it was. I made the rear shift just as he was passing on my left and it popped when he was in front of me.

jadocs

Interesting, I agree it has to be this, or a defect.

Sy Reene

Interesting about the too-much-torque theory.. aren't folks always warning against clamping a seatube when putting bike in a stand for fear of crushing the seat tube (ie. always use the seatpost). I can't imagine those workstands with the rubberised clamps would ever exert more psi on the tube than a 1/2" wide metal FD clamp.

jadocs

I think they are talking about the top tube being clamped, especially with respect to carbon fiber bikes.

With regard to the FD adapter, even in the dealers manual, they warn you to check with manufacturers specifications with regard to torque because the stated 5-7 n.m. may be too much depending on the material used on the frame (I assume they are talking about carbon fiber frames), but I could be wrong.

Psimet2001 

800W won't break anything. Definitely a flaw in the material. Could have been exasperated by how tight it was on the frame and if you were/are heavy and putting that 800W in while yanking on the bars for leverage. Tubes flex and *POP*.

Pay a couple of bucks and grab a new bracket and be done with it.

Psimet2001 

Wrong angle completely. Too tight puts strain on the clamp as well and if there is already a defect in the material then it if the frame flexes at all it will help accelerate a failure.

redlude97

I see a Di2 FD, did you adjust the leverage screw on the FD to push up against the seat tube? If not maybe the front shifting fatigued the adapter

jadocs

Already repaired. Those were seated watts (mid acceleration), so I was not torquing the frame (per se) by pulling up on the bars. I agree 800 should not break anything and it must be a defect.

Yes, the support bolt was engaged. I also double checked it when I re-installed the FD onto the adapter...it's tight and the chain guide outer plate is aligned perfectly.

TimothyH

I think @redlude97 is onto something.

It broke exactly where the 2mm support bolt contacts the band clamp.

See page 28 at https://si.shimano.com/pdfs/dm/DM-DA0001-10-ENG.pdf




My guess is that the support bolt was never tightened properly or tightened too much. It only has to be just barely touching the band clamp.

Odd that it snapped when shifting the rear and not when shifting the front. I would have liked to have heard it blow.

Glad nobody was hurt! I'm going to the garage to check the 2mm support bolt on my Di2 bike right now. Its been about 2 years since I touched it.


-Tim-

jadocs

Huh...that's a great point! Just barely touching huh? Dang it, now I have to go back and double check and hope it doesn't mess with the alignment....brb

jadocs

So I backed it out, then turned it back in until I felt it touch, re-checked the torque and made some fine adjustments on the adjusting bolt and trim.

Psimet2001 

True on the support bolt. In which case it was most likely over-tightened (my guess).