B-screw threads sheared on Shimano

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B-screw threads sheared on Shimano
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Posted: Aug 13, 2022 at 20:19 Quote
On a descent today I noticed my chain was loose and skipping gears. Upon getting home and inspecting I noticed an oddity with my b-tension screw. The washer had seemingly worked it’s way up the screw:

Upon removing the screw, some metal shavings came out:

Unfortunately I can’t get the screw to apply any tension on the derailleur any longer without it backing itself out. Any ideas for repairing this?

Posted: Aug 14, 2022 at 0:08 Quote
Can you actually screw it in anymore? Looks like the thread that the b-screw goes in to has sheared. Warranty?

Posted: Aug 15, 2022 at 13:56 Quote
New thread + new M5.. no ?

Posted: Aug 15, 2022 at 14:49 Quote
vcooley wrote:
Unfortunately I can’t get the screw to apply any tension on the derailleur any longer without it backing itself out. Any ideas for repairing this?

Sounds like the derailleur was bouncing around against the hanger and forced the screw backwards through the derailleur material and stripped it clean.
Here's a fix:
If the screw is undamaged (or undamaged enough) to allow a nut to run up and down then:
(1) Get two nuts that will thread onto the screw
(2) Put the nuts on either side of the derailleur material that the screw goes through.
(3) Run the screw through the first nut, through the material and then through the second nut.
(4) Keep screwing the B-screw against the hanger until you get the right tension.
(5) Then tighten both nuts toward each other - with the derailleur material between them - while keeping the screw from rotating.

You should now have a B-screw that won't ever back out again.

Posted: Aug 22, 2022 at 3:40 Quote
Helicoil or tap a larger thread are 2 of the better options.

But tapping a larger thread and using a new hex screw may be the better option, especially with a little thread lock applied to the screw and left to dry to help prevent the screw moving during use.

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