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My bike has a set of Shimano BR-RS505 hydraulic brakes and the rear pad axle, datasheet item 10, just won't budge.

The flathead screw stripped a little when I tried to release it and I didn't go any further.

My first thought was to carefully apply some WD-40 (all I have) into the screw then use a heat gun to hopefully loosen it off.

I've also been told that the only other solution would be using a small hacksaw to cut through the pin!

How should I proceed? Thanks!

(I have also bought replacement, seemingly compatible, hex screws rather than flatheads..)

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I've also had this problem and managed to damage the slot head to the point of not being able to get any purchase with the screwdriver. Pad axle totally seized.

My solution was to use a dremel tool with a very fine diamond bit and cut a new slot into the head of the pad axle. A little "liquid wrench" and let sit for 24 hours as well (knowing I needed to replace the pads).

This worked and I was able to remove the pad axle.

I put very light coating of grease on the threads of the replacement pad axle in hopes that this would prevent a repeat of the problem in the future.

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  • Excellent point on the assembly lubricant. Thank you for a great first answer, and welcome to the site.
    – Criggie
    Jan 20 at 22:15
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The axle pin is a combination of threaded (near the head) and smooth (body that the pads move on). It would be hard to replicate that part without removing the threading from a hex headed bolt.

To start at the beginning, did you remove the retaining pin before attempting to unscrew the axle/pin? There is a cotter/retainer at the other end of the axle that would prevent rotation if it wasn't removed first.

If all that has been removed and it is still stuck, I would remove the caliper from the frame and try some break free or similar to free the stuck threading. This will ruin the pads (likely), but you are likely also trying to replace them.

If you use a hacksaw to cut the pin, the threaded part will likely stay in the caliper body. If anything, on my own brakes I may use a cut off wheel (like on a dremel) to deepen the slot for the flathead or to make a cross cut and allow Phillips use. After doing either, I'd likely start looking to order a new pin and retainer (part 9) and perhaps look at cleaning of the threading inside the caliper body.

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  • Yes the retainer clip was removed before I tried unscrewing the axle. Thanks for the advice!
    – fham_526
    May 1 '20 at 9:29
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Had this issue myself a few days back.

My solution is as follows. Mind that it is destructive on the pads and damages the pin, but it is the most gentle idea I could come up for the caliper itself.

  1. Delicately cut the heads, i.e., the part with the hole, of the pads and spring (with dremel, saw, angle cutters or a combination thereof), so that you can set them free of the pin.
  2. Remove from below (disk side) the pads and spring

At this point the pin is fully exposed from the inside of the caliper body.

  1. Use a small vice grip to grab firmly on the pin from the inside of the caliper, and unscrew it.

This last step will likely score the pin, but will give you enough leverage to loose the pin free. It is a quite painstaking process because of the tight space, which will only allows to undo the screw by a few degrees of a turn at a time.

In my case, the pin had a few marks from the vice grip, but I was still able to reuse it till I'll have access to a new one (carefully applying some grease on the threads to prevent from locking again but making sure that the grease stays well away from the pads).

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Normally you would absolutely not put WD40 anywhere near your brake calipers. If you do so you risk contaminating the pads with the lubricants that are in that product. However, if you are prepared to trash the pads and thoroughly clean the caliper with degreaser that approach may work.

I'd definitely recomend against using heat on on anodized aluminum part: a heat gun could mess up the finish. I'd very definitely recomend against using heat on a part with mineral oil hydraulic fluid in it.

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  • Okay thanks, what would you recommend going forward?
    – fham_526
    Apr 28 '20 at 8:45
  • The mineral oil heats up while braking. I don’t see how heat from a heat gun is any worse than heat from braking.
    – MaplePanda
    Jan 20 at 22:11
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    @MaplePanda the heat gun depending on model can reach in excess of 1000 degree C, much higher than normal braking conditions and also the heat gun is a constant heat, it wont dissipate the heat like normal riding conditions
    – Dan K
    Jan 21 at 13:25

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