SF2 Front Brake Problem

Bikepirate

Bikepirate

New member
Location
Brisbane Australia
I'm still having a problem with the Brembo Front Brake. I have now changed the the seals etc in the callipers and also replaced the complete mechanism in the master cylinder per the procedure obtained from Paul Marx (bless him!). I still can't obtain any pressure. Fluid comes out through the bleed nipples when loosened

I'm using DOT 3 Fluid. Is this OK?

A mate has recommended pumping the fluid back through the bleed nipples to get rid of any air. Any recommendations on this and a suitable pump kit?

Cheers,
 
You could also try removing the calipers, putting a suitable spacer between the pads and bleeding with them in different orientations. I’ve used a 50cc irrigation syringe with a hose slid over the end to back bleed. Any decent pharmacy should carry them.
 
Sounds like air bubbles are still present- did you use new sealing washers and what’s the condition of the lines. My Brembo fluid cover lists Dot 4. There are reverse bleeders from auto parts shops like Mighty Vacs. Air bubbles might be in the line splitter.
 
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A mate has recommended pumping the fluid back through the bleed nipples to get rid of any air.
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Not a bad idea.
But the air might also be trapped in the brake line splitter.
I always dismantle the splitter from the fork and move it
in different directions, when I'm having troubles bleeding
the brakes. So there'll be a position where the trapped air
will be released.
hth
Ernesto
 
Have you made sure that no air is trapped in the master cylinder? With it removed from handlebar, 1/4 with fluid tilt it lever up and lever down while jiggling the lever to move the piston just a mm or so. Often there will come a stream of bubbles out of the small holes.
 
Tippie said:
Have you made sure that no air is trapped in the master cylinder? With it removed from handlebar, 1/4 with fluid tilt it lever up and lever down while jiggling the lever to move the piston just a mm or so. Often there will come a stream of bubbles out of the small holes.
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Exactly as above, and another go-to is to set the steering to left lock on side stand if you have one to get a good path for air bubbles, then strap the brake lever tight to the throttle grip and leave overnight. This can make a huge difference.
 
Most of all, that the master cylinder has two clear holes below the reservior, one to release back pressure and one to supply fresh fluid from the mechanical movement of the master piston. One hole is so tiny, i use very fine stiff mandolin string to clear, this problem has happened on 3 master cylinders in the last few months, plus the usual angle the master by leaning the bike left to slow crack the master ie not fully engage to bar, only about 10m/m of slow movement to release air at the master banjo, akin to a slow limited pump action.

Reverse fluid via syringe at the farthest caliper bleed nut to the master, ie no fluid in the master at first, reservior. This confirms one of the above holes as clear if not fully clear.
HTH j
 
A big advantage of the Brevetatto "Jota" bars is that you can uncouple the right hand outer sections of the bar from the centre piece, turn it, lever ball up and squeeze the brake lever, gently, several times. This will, unless something else is seriously amiss, give you a firm lever.
Last time I changed a top hose, I bled it entirely using only this method.
Also works well on hydraulic clutches.
 
While you are working on the brakes consider adding a bleed nipple to the manifold (see photo) it expedites the removal of air bubbles trapped higher up, and works a treat.
Years ago I had a problem getting the lever to firm up after changing fluids I found that after pumping the lever and opening the nipples with the lever pulled in got the air bubbles out. When I was certain the air bubbles were gone I pumped the lever cracked open the nipple released the lever before closing the nipple, a couple of times repeating this action and pressure came right up, give it a go.
I assume you are using a clear plastic hose attached to the nipple being bled so you can see the air bubbles or lack of.1708462021226.png
 
since I bought a vacuum brake tool I have no problems to bring pressure in the systems. Sometimes the rear brake is a bit difficult.
Those simple tools are nor expensive maybe 20 €.
 
I use a 50 ml syringe with a short length of windscreen washer pipe to suck fluid through the system from each nipple in turn. I find this works better than pushing fluid back into the system. It works on Guzzi linked brakes so should work on anything😀
 
Normski said:
I use a 50 ml syringe with a short length of windscreen washer pipe to suck fluid through the system from each nipple in turn. I find this works better than pushing fluid back into the system. It works on Guzzi linked brakes so should work on anything😀
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Sorry, but how does this work? I assume that each bleed nipple has an integral ball that only allows a flow one way i.e. reverse flow. I check that fluid is present by loosening the nipple and fluid comes out from the base of the thread.
Or have I got it completely wrong?
 
Tippie said:
Have you made sure that no air is trapped in the master cylinder? With it removed from handlebar, 1/4 with fluid tilt it lever up and lever down while jiggling the lever to move the piston just a mm or so. Often there will come a stream of bubbles out of the small holes.
Click to expand...
Thanks Tippie, I'll give it a go. Also I will check the small hole is not blocked as suggested by iis_iis.
 
Bikepirate said:
Sorry, but how does this work? I assume that each bleed nipple has an integral ball that only allows a flow one way i.e. reverse flow. I check that fluid is present by loosening the nipple and fluid comes out from the base of the thread.
Or have I got it completely wrong?
Click to expand...
A bleed nipple doesn’t have a ball. It allows flow in either direction. That’s why, in normal bleeding, you close the nipple before allowing the lever/pedal to return after squeezing.
 
No ball valve, fluid flows both ways.
What he's suggesting is rather than push fluid through the nipples your using the syringe to suck it through.
Start with the nipple furthest away.
 
There is the old trick of leaving the lever pulled overnight with a bit of inner tube.
In the morning, it's bled.
The bubbles work their way up progressively and slowly.
No acrobatics.
Paul
 
"I assume that each bleed nipple has an integral ball that only allows a flow one way"
very sorry (and brutal) but have to say this state,ent by you shows a lack of general hydraulic motorcycle brake systems, I apologise again becaise I want you to gain knowledge on this, Hamish is absoluetly right the bleed nipple is just a taper end bolt with a hole to atmosphere above the tapered end which is its seat/seal.

iiS John is very likely right, strip the master cylinder to its bare bones, use brake cleaner and an air line to clear that tiny (of the two) holes of clag, which you have very likley missed, I use gas welders nozzles and a strand or two plucked from a wire brush, this will mean fitting (another) seal/piston kit to the master, since it is held in place by a crush washer which is not re-usable, to get the gubbins out. remove the hydrauluic hose union to reveal a female thread in the body, remove lever (obvious) and then, holding it gently in a vice (avoid crushing the cylinder) use a long pin punch to drive the kit out, no doubt as Points Marx previously advised you. Having two people on hand to bleed is helpfull, in, in, out, out, in, in, out, out. should be heard as the lever is pulled in the nipple is open, as the lever is let out the nipple is closed.
CLEM
 
CLEMTOG said:
"I assume that each bleed nipple has an integral ball that only allows a flow one way"
very sorry (and brutal) but have to say this state,ent by you shows a lack of general hydraulic motorcycle brake systems,
Click to expand...
They are ACTUALLY available 9-)
 
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