Leaking front caliper - 2018 KTM 790 Duke Forum
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post #1 of 6 (permalink) Old 10-19-2019, 11:08 PM Thread Starter
rft
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Leaking front caliper

Beginning to get a bit frustrated, doesn't
KTM understand how seals work, first it was the sump, then the countershaft now its my front caliper - grrrrrrrrr!!!! never had so many problems with a new bike before.

Never replaced caliper piston seals before, can anyone help pls - dont say dealer as they are 150 kms away and are mostly dirt bikes - the only thing I would trust them with is an oil change.

Done lots of web searching, lots of videos for simple things but nothing for seals, the repair manual says nothing, any help out there.
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post #2 of 6 (permalink) Old 10-20-2019, 03:24 AM
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Changing Caliper seals is a doddle. The key is CLEANLINESS and PATIENCE. Have LOT'S of clean brake fluid to flush rinse parts. I would also suggest finding some very very fine abrasive - CROCUS grade or Jewellers rouge in case you detect any burrs.
Get some Plastic watchmakers tools off e-Bay. That or some dental picks - though you need to round the tips off.Will help get the old ones out - without scoring the caliper.
That said - On a bike in warranty - I would demand a new caliper as it could easily be a casting failure. They are rare but if you replace the seals then you will always be to blame.

The other option would be a Brembo Upgrde.
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post #3 of 6 (permalink) Old 10-20-2019, 10:02 AM
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This one is pretty strange. New bike? I'd take a trip to the dealer and have the faulty caliper replaced.
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post #4 of 6 (permalink) Old 11-05-2019, 02:19 AM Thread Starter
rft
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Bit slack, finally got around to replacing the brake piston seal after couple weeks waiting for parts.
Turns out it was a piece of cake replacing the seals.
But I'm having a problem getting all the air out of the system, I have brake operation but lever nearly back to the bars. My usual basic brake bleeding technique doesn't seem to be working very well.
Any suggestions
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post #5 of 6 (permalink) Old 11-10-2019, 03:24 AM Thread Starter
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Well I finally sorted the air in my front brakes, in the end it was just a 2 min solution.

This is what I did, I removed and replaced rhs brake piston seal that was leaking, started filling system with fluid, bled both front calipers until no air bubbles (takes a while).

At this stage the brake lever still comes back to the bars but the brakes do work - just. I pulled the brake lever back to the bars, fixed with a cable tie and left overnight for any bubbles to rise up the lines.

This is the part that had me stumped. The master cylinder has a very small bleed nipple tucked away on the lhs between the bars and the master cylinder. I simply bled this nipple until the bubbles stopped and hey presto instant hard brake lever.

Never seen a master cylinder bleed nipple before, I'm sure lots of bikes have them but I have never seen one before.
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post #6 of 6 (permalink) Old 11-10-2019, 10:51 AM
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Originally Posted by rft View Post
Never seen a master cylinder bleed nipple before, I'm sure lots of bikes have them but I have never seen one before.
Yes. Most if not all radial M/C have them for years. As they represent the highest point in the system, it is extremely important to bleed them.

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