ASK THE MXPERTS: IS THE CLUTCH SLAVE UNIT ON MY HUSKY FC450 GOING TO FAIL?

This is where the Magura slave unit lives. No need to knock.

Dear MXA,
I know that MXA says to replace the stock Husqvarna FC450’s Magura clutch slave unit’s piston and seal with the KTM parts, but my Husqvarna dealer says that there is no such part. He said that if I wanted to switch to a Brembo slave unit, I would have to buy the complete KTM clutch system—lever, master cylinder, hose and slave unit. Can you help me?

We hear this all the time. In fact, we know a famous motorcycle racer (now a Vet) who had the slave unit on his Husky FC450 go out at the track. He thought that he had burned up his clutch. We looked at his clutch and told him that his clutch was fine but that the seal on the internal slave unit piston was bad. We suggested that he replace the Magura piston with the Brembo piston out of the KTM 450SXF. His dealer told him that it couldn’t be done and to put in a new Magura piston and seal. Of course, a month later, the Magura seal failed again. He eventually went to a KTM dealership and bought the KTM parts and had a different mechanic put them in his bike. We know that a Husqvarna dealer doesn’t have access to KTM parts, even though the two engines are identical (save for the Magura clutch slave unit), but we also know that the Brembo parts fit perfectly in the Magura unit. The Brembo piston has a much better seal than the Maguras. The KTM part number for the slave unit rebuild kit is 5483-2066-000. It retails for approximately $50. 7602 Racing also makes an aftermarket slave unit piston for the Husky FC450.

This is 7602 Racing Magura slave unit piston.

It’s not that every Magura clutch slave unit will suffer a seal failure, but MXA has had three failures in the past two years. How can you tell that it’s a seal failure instead of a burned-up clutch?

(1) When you are riding the bike, the clutch goes completely away. You pull the lever and nothing happens. There is no warning.

(2) A burned clutch smells. A seal failure just loses pressure inside the slave unit.

(3) It is almost impossible to burn up a Husqvarna or KTM clutch that was working perfectly when you went out to ride. Husky and KTM clutches are self-adjusting, which means that the hydraulic pressure compensates for heat and wear. This is why you never have to adjust lever play before a moto.

(4) Often, after a Magura seal failure, the clutch will begin working again once the bike cools down in the pits. Don’t be fooled by this. It will go out again as soon as it gets hot.

As for the 2019 Husqvarna FC450, Magura did upgrade the seal for the new model year, but we haven’t starting testing the 2019 FC450 yet (we start next week), so we don’t know if they fixed the problem or not. We assume that they came up with a solution, but they did not switch to an O-ring as on the KTM slave piston.

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