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I am trying to unmount my rear derailleur. However it seems to be seized and I am unsure how to proceed.

See the pictures below.

The current state of the derailleur is as follows:

  • The screw inside the frame (C) is not seized and can be moved a bit
  • The B-limit plate is not stuck against the derailleur, i.e. the gap at (A) is not seized.
  • The 5mm hex key (D) is in good condition, so I can get a relatively good grab there
  • However, the gap at B is seized - feels like it's welded together :-(

I already tried soaking everything in WD40 and applied lots of force on the screw at (D). However, I can only wiggle the derailleur unit as a whole for a few degrees, before I can no longer do anything.

What would be the next steps to try unmounting the derailleur?

Top View Inside View Outside View

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  • Can you say why you're taking the rear derailleur off? And the exact model of derailleur?
    – Criggie
    Apr 15, 2023 at 12:47
  • 1
    I'm taking it off to replace it. The current one is a SRAM Apex 1, I'm replacing it with a SRAM Rival 1. Apr 15, 2023 at 12:50

2 Answers 2

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It appears that the pivot bolt is corroded solid with the body of the derailleur.

WD40 doesn't do much for aluminum oxide corrosion. You could try a torch on the affected area. Direct it near the pivot bolt head and the outside of the derailleur body where the pivot bolt runs through.

If saving the derailleur isn't important, you could just section off the corroded area with a dremel cut-off wheel. Make one cut like so and another on the other side. Find a line where you won't run into the frame. By taking off pieces in that area, you'll likely be able to get the pivot bolt moving.

enter image description here

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  • I'm accepting this answer, as this is pretty much what I did. I cut off the B-limit plate and the adjustment screw with a hand saw. After that I was able to rotate the whole derailleur and unscrew it that way. Apr 16, 2023 at 16:05
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Well that's a puzzle ! I am not familiar with this derailleur, so here's my guess:

You appear to have a bike frame with an integrated hanger, as in not easily replaceable. So any damage could write off the frame. This means you need to be careful.

In your first photo, the green paint is part of the frame, and all the black parts are part of the derailleur, that junction is what should separate. So all the black parts are coming off and should be in one connected piece. B does not separate from the derailleur.

The hanger will have a conventional right-hand threaded hole, with a M10 thread on the inside. That is what holds the derailleur to the frame.

I think you need a 5mm hex driver inserted from the right hand side, through into D and then a lot of force in an anticlockwise direction. However avoid using so much pressure that the hex strips.
You might be able to put the 5mm hex tool in from the wheel side, but remember that flips the rotation too.

Causes I suspect some of the paint has bound up the thread, or perhaps a bushing has been tightened excessively and is now binding.
This looks like a newer groupset on an older frame, so its possible some fettling was needed to fit it in the first place.

Also, it's not impossible that whoever fitted this unit used threadlocker. You could try heading the bottom of the hanger with a hot-air blowing gun for ~1 minute, or a hairdryer for 3~4 minutes. If someone used high-strength threadlocker then you'll need 400-600 degrees, which will burn paint and risks damaging anything not metal. Penetrating oils do nothing to threadlocker.

If the hex strips out, then you'll have to use a reverse bolt-remover, or drill the center bolt out, and the derailleur will be unusable. Do NOT damage the hanger-area of the frame at any cost.

Most quality hex drivers are made from tool steel and can take a hammer to get them started. I've also had good luck using a manual impact driver (the sort you hit with a hammer) but the whole dropout area would have to be supported from behind. I've never used a powered impact driver on a bicycle (Don't own one) but that level of power is likely too much.

Good luck!


Here's a parts-kit for a SRAM Apex 1 mech where it goes into the frame:

enter image description here
From https://www.sjscycles.co.uk/gear-spares/sram-gx-1x11-b-bolt-limit-screw-kit-for-11-speed-rear-derailleur/

So the main chunky pin has the M10 thread on it for hole in your frame's hanger area. This is labelled B in your photos, supporting the need for a 5mm Hex driver.

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