Brakes won’t bleed

[Nobby the Bastard]

If you don't know how to fix brakes (and you clearly dont) why risk someone's life?
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[Bhud]

Get it checked over by a mechanic before trying it out on the road.

[Weisse Schlange]

There is a leak.
It's letting air in, as demonstrated by the vacuum pump losing pressure when you open the nipple.

Find the leak, and fix it.
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Hing Oan

[Bhud]

It's easy to draw in air through the bleed nipple if it's too loose, or if the threads around the bleed nipple are damaged. That's why I say, just bleed the brakes the normal way. I've done this lots of times, but I'm not a mechanic. I prefer to do this the normal way, i.e. pump it from the lever or pedal. Once you've got some pressure, you've got a starting point and you can do whatever you like.

[bikenut]

Nice clear picture of the res floor...

You should see two holes in the floor, one larger one near the pedal end, and a tiny one nearer the hose end, the pressure end of the MC.

The larger hole you will see the piston below.

The tiny hole you will see nothing apart from a column of tiny bubbles rising when the MC is filled with fluid initially, and the unit pumped.

There is white crud or something where I would expect to see the larger hole.

The tiny hole would be in the "countersunk" hole as seen in the picture.

You ultrasonically cleaned the unit, but is that very important tiny hole absolutely clean and clear !

It must not be blocked else the system will not work properly. This tiny hole is about 0.4mm diameter.

You have a guitar ?

Compressed air is good, so is hydraulic pressure using the caliper, but be weary of a "her or stream" of fluid coming out, and spraying onto the workshop ceiling !

The hole is tiny so needs hi pressure to clear...

The light method is good to "see" that the hole is clear.

Fluid will pass through this tiny hole by gravity/Syphon, the initial stage of bleeding.

Bleeding can be started via gravity method, to fill the hose and caliper, but an assistant is usefull unless you have a third hand.

With system initially bled/primed, move onto the pumping procedure...never let the fluid level in the res get too low.

Pump up the pedal say 5 times then hold down the pedal, open the caliper bleed nipple quarter of a turn and watch fluid and bubbles flow out, then tighten/nip the nipple.

Then let go of pedal, count to 5, time for the MC system to "refill", then repeat process.

Good communication is needed between you ( you are giving the orders and in charge !) and your assistant. Commands like pump up, down and let go are good.

Yes an air leaks at the nipple can be problematic, as can air drawn in past the MC open end piston seal.

That tiny hole must be clear, and your assistant obey orders given, only letting go a the pedal when ordered to do so.

You could back bleed, fluid entering the red by that tiny hole, or pressure bleed via an airtight fluid tight Res cover, tube and outside fluid Res, or similar.

So, caliper clean with all components as they should be, fitted to bike. MC unit clean with all components as they should be and fitted.

Res full, pedal used to prime, allow to gravity bleed. When bubbles from tiny hole and nipple tube are no more, bleed via pump up, holding pressure, opening nipple and watching fluid/bubble flow, untill no more bubbles.

You did "wet" the MC bore and seals during assembly ?

Learn the procedure etc., or get a wig.

Ps don't break a probe in that tiny hole !
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nuts about bikes

[Farmingstock]

Thank you for the responses especially bikenut, I’d say the brakes are 99 percent there now and will be taking the bike for an mot so I’m sure they will tell me if the brakes are right now, if not I will get them to fix! Thanks again

[steve the grease]

See that scrape on the side of the piston? I wonder if there is a similar scrape on the inside of the cylinder- it looks like some grit or something has got in there. If the cylinder is damaged, then the seals on the piston in the master will always let a bit of air in. You could try honing it with some ( very fine) wet and dry wrapped around a pencil, if it is scored. I spent a fortune on getting a Bedford master cylinder lined in stainless, within a year it was leaking due to some moisture causing corrosion between the piston and the bore.
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All the above is my personal opinion, you can see my lips move, but I'm talking out of my arse.
I've been riding, and fixing , bikes for 50 years, in that time the more I learn, the less I am absolutely sure of.....