Have I bought a duff front master cylinder / reservoir?

[Asian Boss]

I'm trying to improve one of my old Honda XLs, the one with the weak front brake.

I suspected the front master cylinder seals had failed as the lever came all the way back to the bar without putting much pressure on the brake pads - and bleeding didn't help.

I bought a new master cylinder / reservoir combined unit. A patters one from the states. It looked good. I fitted it, filled it and couldn't get it to bleed or even begin to push fluid or build pressure. I realised I probably needed a new hose too so left it.

I bought a new hose and went to fit it today. I disconnected the old hose from the new master cylinder. I was expecting some fluid to come out of the master cylinder - but nothing came. I looked into the master cylinder connector where the hose joined and it was dry. I tried pumping the lever a little - nothing. I tried pumping it more - still nothing.

Could it be a duff master cylinder? There isn't a cap or something to remove before use is there?

With the top off the reservoir I can see the master cylinder moving through the apertures, which from (distant) memory looks right.

[Asian Boss]

FWIW a pic from above - I took it off the bike.

DSC_0551 (Medium).JPG (338.63 KiB) Viewed 194 times

[Le_Fromage_Grande]

You've got an air lock, pump it slowly with the bleed nipple open, could take an hour or more

[Asian Boss]

How come none comes out of the master cylinder itself with the hose not connected? I'd have thought I'd see it coming out of the port where the hose screws on.

[KungFooBob]

For £500 plus expenses....

[Hairybiker84]

I've had it before where a master cylinder won't draw in the fluid, whether it's an air bubble or assembly lubricant, who knows? If you've got a vacuum bleeder, try and draw some fluid through it first. If not a small syringe with clean fluid and try and force fluid back past the piston into the reservoir. Once the master cylinder has actually got some fluid around the piston and internal seals they've worked ok for me.

[Asian Boss]

I've had it before where a master cylinder won't draw in the fluid, whether it's an air bubble or assembly lubricant, who knows? If you've got a vacuum bleeder, try and draw some fluid through it first. If not a small syringe with clean fluid and try and force fluid back past the piston into the reservoir. Once the master cylinder has actually got some fluid around the piston and internal seals they've worked ok for me.

Thank you.

I don't have a vacuum bleeder. How would you connect the small syringe? I assume to the caliper bleed nipple with some hose?

[David]

Dissconnect the outlet pipe. Apply finger tip to hole. Pump steadily , release finger a little...repeat until you get brake fluid in your eye. Assemble.Bleed as normal.
BE SURE BLEED NIPPLE IS AT THE TOP OF THE CALIPER.

[wull]

[DefTrap]

I always prime these old skool systems by sucking the fluid through with good old fashioned lung power.
You need a longish bit of tube on the caliper nipple, just in case, because brake fluid is foul.

[Mr. Dazzle]

I was gonna say the same.

Put your gob over that 'lid' opening and blow as hard as you can Or use a hose as above, your choice.

The absolute best way to do this is to build everything 'underwater'. A mate of mine used to work at an Ohlins centre, they had massive tanks of hydraulic fluid with the 'rubber gloves through a window' thing. It means you can build suspension units, callipers etc. fully submerged in oil. Absolutely brilliant for avoiding air locks.

Don't have access to that any more

[Asian Boss]

Cheers chaps, I'm going to have a go at a range of these techniques. Once the correct length brake hose arrives. The one I ordered was the same length as the old, incorrect one!

I have a big syringe somewhere in the garage to use rather than my gob.