Sticky jammed RF coupling arm in M240

[BryanC]

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Hi everyone. My M240's rangefinder coupling arm has suddenly gotten stuck. It will spring back forward toward the mount if nudged but when moving through its range it's got a sticky, gritty feel hat wasn't there before and definitely isn't normal. It feels like it's rubbing on something but I can't see anything.

It's probable that it's my fault. I adjusted the roller cam (using a hex-wrench) to correct an infinity alignment issue. I was cautious, and I've made adjustments like this before. It was actually successful, or so it seemed. Then I made one last tweak and mounted the lens again, and the RF patch suddenly wasn't moving back after focusing to infinity.

I've heard that the mechanism under the top cover can sometimes require lubrication, but that seems pretty coincidental to say the least.

If I have to send it in for repair I'll bite the bullet. But if anyone has any ideas I'd be grateful. Thanks!

[BryanC]

The problem seems to have cleared itself up. At least for the moment. Some other folks who've had similar problems seem to have reported the same thing. Uneven lubrication, maybe? 

I'll see if it recurs and re-evaluate from there.

[jdlaing]

Sometimes mounting the lens without lining up the red dot can strike the arm and jam it a little.

Glad you got it normalized.

[plaidshirts]

I just had a similar episode. I was mindlessly exercising the focus ring of my Summicron 40 mounted on my M-D 262 when I heard ticking noises as it traveled to close focus. I didn't think much of it, but when I looked through the viewfinder, I saw that the patch would stop then snap into place with the "tick". Thinking it was perhaps the lens, I tried my 50 but with the same result.

I unmounted the lens and noticed the coupler wouldn't bounce back after being pushed down. Somehow, after a few minutes of dickering around, the arm is free and working like it should.

I've googled this and seen a few posts across different M models with similar stories. For those that had this happen, has it reoccurred? I'm hoping this is just a fluke incident...

[a.noctilux]

Yes this was only once, so long ago with one of my M4.

Never had the same sticky roller again.

 

The repair man replaced the spring (or sort of), then the thing worked untll I sold the M4.

[Jean-Michel]

Never had an issue with this for decades, and then it happened with my M-P and that required a trip to Leica. I did see a video on how to get to the mechanism but was not interested in doing all that work, so it ended up in a cla that cost me about $500 Canadian.