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I have Quad QHD-4 Axis Disc Brakes that were probably never maintained and are stuck. There was a lot of grime and dirt all over, the pads even rusted a bit. It probably locked due to this and I also pressed the lever after removal before I knew. For the life of me I cannot move one piston all the way in. I used a flat headed screwdriver and applied all my body weight to the screwdriver but still it would not move. Brakes are bled and completely taken apart except from the large torx screw. I even tried spraying WD-40 but it had no effect.

Is there anything else I can try? Would I be able to remove the pistons if I removed the large torx bolt? If so what bit is that? I cannot find any info on how to do this. It doesn't seem like the pistons can be removed without undoing the torx bolt and I think it would need to be cleaned well before use due to corrosion, dirt and WD-40.

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You pretty much have nothing to lose by disassembling the calipers and attempting to free the pistons. They are useless now, so if you break something it does not matter.

You may try contacting the manufacturer (Hayes?) and asking if they have a service manual.

The silver cap with the Torx socket does seem to be the way into the internals. If you can measure the point-point distance with some accuracy (1/10 mm) you can look up what size it is. The Wikipdia page on Torx drivers lists the sizes. If not, take a caliper to the tool store and try different sizes until you get the right one.

It's the inboard piston that is stuck so if you can take the outboard one out you should be able to carefully drift the piston back in with a short length of wooden dowel or brass rod (old door hinge pins work well) and a hammer.

I could not find any info on these particular brakes online but you could look for other videos about how bicycle disc brakes work so you know what to expect when you get in there. Park Tool posted one recently. It's informative, if a bit silly at the beginning.

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  • It looks like T60 bit. I don't have a torque wrench now, do I need one? It does seem like a simple screwdriver would not be enough, maybe L-key would work? I wouldn't mind getting a torque wrench but I feel like it wouldn't get much use, is there something more useful on a bike as opposed to the 40cm length type ones that I assume are mostly for cars? – DominicM May 6 '18 at 11:43
  • @DominicM You only need a torque wrench to do the cap back up, and unless you can find the torque specification, having a torque wrench is no use. You could get a suitably large L-wrench (like a hex wrench, only with a Torx head. - or - you could buy a small socket set which is generally useful plus a T60 head that fits it. – Argenti Apparatus May 6 '18 at 11:53
  • Just FYI there are bike specific small torque wrenches that cover the range or torques used on a bike. Examples are Park Tool's TW-5.2 and TW-6.2. – Argenti Apparatus May 6 '18 at 12:04
  • If you need a torque wrench once, you'll need it again. Consider buying one. If you will never ever use one again, try hiring one or talk to your local bike shop or your car mechanic. – Criggie Jun 4 '18 at 22:51
  • I did actually end up buying a Wera 1-25nm torque wrench. Total overkill as it cost more than the bike :) In fact torque wrench is the wrong tool here too. Torque tool is used to tighten things accurately, breaker bar is used to undo it and is a fraction of the cost. There is also no nm value given for the breaks so it's not even useful for tightening it back up. – DominicM Jun 6 '18 at 9:07

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