gauvins

Is it just me or there is something unusual with the fastening of (Shimano XT) rear derailleurs?

I've had no issues with the first two bikes that I've assembled. But today it looks as if the thread has been stripped, following 30 minutes of unsuccessfully trying to get the derailleur to engage in the mount. This on a new Surly Troll frame. I suspect that some paint had messed with the thread. But is could also be me (I remember struggling to remount my RD at the airport).

Is there a trick? I mean, it looks rather basic.... Could it have something to do with the equipment? (Shimano XT-RD780 on Surly frames / LHT and Troll).

CliffordK

If you are re-mounting the derailleur, then the paint should be irrelevant.

BE GENTLE.

You may need to use a tool to get it started, but don't put any force on it.

Be careful of the B-Screw adjustment tab. Make sure it is behind the notch. Maybe drop the chain while mounting the derailleur.

If you can't see where you're working, figure out how to get it high enough to see what you're doing.

I have a habit of screwing screws backwards until they feel ready to go forwards.

HillRider

+100. Rotating the bolt backwards until you feel the thread leads match is, or should be, standard procedure, particularly with fine pitch threads like these.

wschruba

Looks like the thread is stripped, or actually stripped it installing the derailleur?

If the former, run an M10x1 tap through the hanger from the wheel side to make sure everything is copacetic. If the latter, you'll need to use a 'dropout saver' to fix the problem.

I've almost never seen problems with (male) threaded parts, just the corresponding hole in the frame. If you're 100% sure it's not the frame (thread in a 10mm axle?) then you can use a metric thread file to clean the starting point of the derailleur's mounting bolt.

Clem von Jones

Maybe the derailleur arms and cage are impinging on the hanger. Sometimes you have to straighten the parallelogram with one hand while you thread it with the other.

Bill Kapaun

Are you trying to install it with the chain threaded through it?
That certainly makes things more difficult.

CliffordK

One other thing.

If something isn't working. Stop and figure it out before you make it worse. Don't force.

Aluminum (or Carbon Fiber) dérailleur hangers are cheap and easy to replace.
Steel, not so much.

gauvins

I was installing a brand new derailleur on a brand new frame. No chain yet.

I very much doubt that the male part (the derailleur) is damaged. Looks like the frame has been stripped. Went to the LBS who sold me the frame and the plan is to tap the hole.

I asked because I am always surprised by how finicky this is compared to, for example pedals. (or any of the several screws one needs to tighten when assembling a bike).

I appreciate the back motion to engage the thread. I believe that I do this instinctively when a screw/bolt doesn't want to engage normally.

I also realize that I do not have a bike stand so I am not well positioned for the job. But then again, pedals are never a problem while the RD is always reluctant.

Oh well...

Andrew R Stewart 

I find that using a tool which has a straight section of the hex shaft allows a better visual lining up of the mounting bolt and the drop out. Or in other words a "L" wrench or multy tool can allow too much flopping around that you might not see easily as you try to line up the bolt while turning it. Andy.

gauvins

Interesting. As a matter of fact I used Y-shaped Allen to mount the first two derailleurs, but an L-shaped for the third.

Still does not explain why derailleurs are (for me) a PITA to mount. I'll ask the mechanic...

HillRider

I've built up two Surly frames, a Cross Check and a Pacer, and both of their derailleur hangers had paint in the mounting hole that had to be cleaned out before the derailleur threaded in properly. There was also paint in the other threaded openings such as the water bottle bosses and rack/fender eyelets so plan on cleaning them out also.

Andrew R Stewart 

One thing about replying to these types of threads is that one can't expect some posters to know even the most basic steps in their project. Like cleaning out threads of any paint or other hindrance to screwing in a bolt.

But I forget this and tend to assume some awareness does exist.

BTW one can try threading a bolt in from the backside to help clean up the frame hanger's threads. Andy.

gauvins

Also a good point. I specifically asked the LBS to prep the first 2 frames (surface bottom bracket, install headset and put anti corrosion oil). Assumed this had been done for our third frame. The bottom bracket looked ok. I didn't check thoroughly the rear derailleur hinge.

dsbrantjr

Never assume anything. Look/feel/measure for yourself.

fthomas

I share your frustration. I just swapped out rear derailleurs on a fairly new Jamis Aurora Elite. It was a major PITA getting the screw started for the new derailleur. I guessing I fiddled with it for almost 45 minutes before I got it to lineup and engage. I was working with a work stand and had the thing almost at eye level. I found that using the long end of the hex wrench allowed me the visual clues as to whether or not the attachment bolt was straight. I kept turning it out until I would hear a click and then try to get it started.

Patience and perseverance! Good luck! Hope you don't need to use a tap, which always worries me if it isn't done carefully!