KTM Clutch Slave Cylinder Rebuild Fail

SeaClassExpert

Hi All,

Rebuilding a brembo slave cylinder with all new piston and o-rings, but I cannot get the damn piston and spring to rebound! I've done it probably 50 times, but can't seem to get it working. I swear, something is out of whack and I cannot seem to figure out why this rebound is not happening.  Anybody have any thoughts?

 

For reference; https://youtu.be/a1TNqI2puH8?si=-7jmPoaZnrYgyFb5&t=337

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ithinkitsbroke
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ithinkitsbroke 6/17/2025 10:17am
6/17/2025 10:17am

OEM repair kit or aftermarket? I had an All Balls kit with a seal that wasn't sized correctly - caused the same problem. I would suggest trying the piston that was removed (assuming it's in good shape) with the new seals and see how it works. Definitely check that there are no burrs or scrapes anywhere on the sealing surfaces too.

SeaClassExpert 6/17/2025 11:40am
6/17/2025 11:40am
ithinkitsbroke wrote:
OEM repair kit or aftermarket? I had an All Balls kit with a seal that wasn't sized correctly - caused the same problem. I would suggest...

OEM repair kit or aftermarket? I had an All Balls kit with a seal that wasn't sized correctly - caused the same problem. I would suggest trying the piston that was removed (assuming it's in good shape) with the new seals and see how it works. Definitely check that there are no burrs or scrapes anywhere on the sealing surfaces too.

OEM straight from Rocky and the mating surfaces are pristine. I think I got a bad piston or something that was oversized.

ithinkitsbroke
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ithinkitsbroke 6/17/2025 12:10pm
6/17/2025 12:10pm
SeaClassExpert wrote:

OEM straight from Rocky and the mating surfaces are pristine. I think I got a bad piston or something that was oversized.

That's what I would suspect as well. Not much else there to cause issues like that. Good luck!

erik_94COBRA
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erik_94COBRA 6/19/2025 10:13am
6/19/2025 10:13am

Have you compared sizes of pistons and o-rings (new vs old)?

Also, using the right fluid?  Some use brake fluid, some use mineral oil.

Sometimes o-rings will swell slightly when exposed to brake fluid.

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