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Ducati 600ss brake bleed getting nowhere
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I own a Ducati 600 supersports (money-pit), and have replaced the front
brake caliper as the old one had 3 out of 4 pistons seized. It's a hydraulic
system, master cylinder on the handlebars down to a 4-piston caliper (2
opposite 2) on the wheel. I've checked, double-checked that everything has
gone back OK, and I have spent nearly a day trying to bleed the air out
since the system was sealed, but am still left with no resistance in the
brake lever. I'm using a hose on the bleed valve, I am keeping the res
topped up with fluid (new DOT4), I drained the system before starting, and
am using a jam jar to catch the fluid and keeping the other end of the hose
immersed in this fluid.
I have tried leaving a rubber band holding the lever in while I do other
stuff, there are absolutely no leaks, and I am positive that no air is
entering. The fluid is returning to the reservoir, as it squirts out if I
try pumpimg the lever with the cover off, but I am getting pretty much
nowhere with the bleeding.
I started out getting some big bubbles, but all I get now is either good
fluid, or tiny bubbles like a fizzy drink out of the bleed valve. Am I
missing something, or should I just carry on and the air will eventually
escape? I've got a jam jar with about 3 quarters of a litre of new fluid
that's come out of the system via the bleed valve and hose, but still no
resistance on the lever.
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Look for high spots in the system where air may collect.
You might want the caliper loose instead of mounted.
The master cylinder should be the highest point in the
system with a straight shot from the caliper up to it.
Teflon tape or grease around the nipple might a help. Moving
things around a little might also help dislodge any residual
bubbles.
When I replaced a caliper, I used a syringe to draw out
fluid. After it sat overnight, the last of the sponginess
had gone away.
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Any help much appreciated before I have to re-mortgage the house for more
parts from Italy..... Thanks!
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Here's the trick when getting all the air from the Master
Cylinder/system after the fluid level has been allowed to drop low.
1:Top up the MC with fluid.
2:Undo the master pipe off the front of the MC
3:Get correct spanner ready
4:Have one bleed nipple open at one of the calipers(Right hand
side/OS) is best as you can see it with a 1-way brake bleed kit.Any
cheap one from a high street Auto-shop will do.
5:Place thumb/funger on the MC hole to seal it and pump the
lever.Within a couple of pulls of the lever the pressure/fluid will
come through.
6:Hold lever in and quickly attach back the MC hose/pipe.
Then continue bleed at caliper nipple and finish off.
The MC usually needs a,"Back" pressure to allow the system to pressure
up.Your thumb/finger is this,"Back Pressure".
HTH :)
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Buy a Mityvac and grease the nipple threads before bleeding.
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If desparation sets in, you could try it the other way round and use a
big syringe to pump brake fluid in from the caliper end.
Grease the nipple threads, to stop air being drawn in around them.
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Air being drawn in - that could be the problem.
Is the OP closing the bleed nipple before releasing the brake lever?
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Teflon tape works well on the bleeders as well.
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2 suggestions:
Make sure the two little holes at the bottom of the master cylinder are
clear, poke a needle in or something.
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That's a good 'un. Happens a lot.
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Wgen there's significant air in the system, as when you replace a
component, the idea is to get the air to rise up into the master
cylinder. Position the handlebars so the master cylinder is at the
highest point. With the bleeder on the caliper CLOSED, squeeze the brake
lever gently, you should see bubbles rise out the recently cleared holes,
a bit every squeeze. Tap the lines every now and then to make the bubbles
rise and make yourself feel better.
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Bike on the center stand, turn the wheel side to side a few times too.
Wheel pointed left ought to put the MC at it's highest point. Also
helps
to loosen the bar clamp slightly and rotate the MC and lever.
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I'd be tapping the calipers, too. And the unions, joints etc. all the
way up. I'd be tying the lever back to the bar and leaving it
overnight, too - surprising how often that sorts these nasty bleeders
out.
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Don't forget to close the bleed nipple before releasing the lever.
Check that all the unions are tight otherwise air might be getting
in - you did replace all the copper washers when you rebuilt it?
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Not strictly necessary. Hit them with a blowlamp to get them red hot,
then let them cool.
They're now annealed and nice and soft.
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To be honest I always had problems bleeding brakes until
I followed the exact instructions in the Haynes book and
it worked a treat.
If all else fails I have a good master cylinder for it as I swapped
mine for a twin disk system so fitted a 916 m/c and then swapped
it again for a Brembo radial...
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Could be an air bubble trapped in the line that floats up quicker than
you can pump it down, but doesn't have a straight shot back to the MC.
I have heard of hanging the calipers higher than the MC so that bubbles
float up to them. An other possibility would be to remove the caliper
from the disc and put something thinner than the disc between the pads.
Pump the pistons out to fill the cylinders, then push the pads back in
to force fluid back up to the MC.
Bruce Richmond
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