Hey guys, this isnt a frame building question, but a modifying question (this seemed the most appropriate forum). For tire clearance and smaller-than-stock chainring reasons, my top mount bottom swing front derailleur wound up having to be mounted with the derailleur clamp directly on top of a bottle cage boss. the slight bump out of the boss causes the derailleur clamp to not fully contact the tube throughout its circumference, and there are slight gaps between the tube and clamp (on each side of the boss). I was still able to clamp it on snugly, but im concerned the extra stress on the clamp. I was thinking i could grind the boss flush with the frame, but not sure if the threaded portion will then fall into the frame (im thinking its a rivet type of thread insert). What should i do? Leave it the way it is, or grind off the boss (will it weaken the frame?)? I have ridden it once this way, and the derailleur did not move, and is still mounted tightly.
Nickbm3
Since you didn't post any pictures or give us any idea what you have, the best suggestion is to get the correct derailleur.
and if you're not going to get the right derailleur, then don't grind on the frame, grind/file the clamp.
I'll take some pics of the situation when I get home. I like the idea of notching the clamp of the derailleur though, I guess the clamp itself doesn't have a whole lot of stress on it normally anyway. I wasn't sure if grinding off the boss would structurally affect the frame.
Alright heres the pics, i couldnt get any good shots to show the gap though, its a very slight gap.
The bottle cage bolt you can see is the top one, the lower one is covered by the part of the clamp where it says "Shimano". Also the derailleur is a Deore XT FD-M771 FWIW
The bottle cage bolt you can see is the top one, the lower one is covered by the part of the clamp where it says "Shimano". Also the derailleur is a Deore XT FD-M771 FWIW
Attachments
Unfortunately not. My bike came with that style der, but it was originally a dual sport bike with 700x38 tires so clearance between tire and the pull mechanism of the der was no problem... now im running 29x2.0, and with the stock der, the tire rubbed the pull mechanism even at the lowest PSI. I looked at several derailleurs and the only way to solve the tire problem was to switch to the down swing variety. everything was great until i changed cranksets to have better gearing for my style of riding, and the smaller chainrings required the der to move down, and just happened to be right on that lower boss :madman:
The mount feels tight, should i just leave it? or notch the der clamp as mentioned earlier so as not to modify the frame?
The mount feels tight, should i just leave it? or notch the der clamp as mentioned earlier so as not to modify the frame?
since you have a top pull setup would removing (cutting off) the cable pull cam that is used to re-route the cable for bottom pull gain you the clearance you need?
Nah, at least not the stock one. Below is a pic of the stock der. Everything was fine with the old chainrings since the new bottom swing derailleur was higher. I really dont have any budget to be buying any more bike parts right now anyway, the only reason I got the new crankset and cassette was because they were from Santa :thumbsup:customfab said:
please excuse the bug in the derailleur
Attachments
Drill a hole in the derailer mounting band to clear the water bottle boss. The bottle boss can now be referred to as a locating dowel. 
In the event something goes wrong, it will be cheaper to replace a modified derailer than to replace the frame.
In the event something goes wrong, it will be cheaper to replace a modified derailer than to replace the frame.
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
