81 XJ900 Frnt Brake Master Cyl problem

hey folks,
I've tried searching for an answer on the site but haven't found exactly what I'm looking for. The problem is I rebuilt the front brake master cylinder on my 83 XJ900 and it won't pump any brake fluid. I've tried pumping the brake lever about a hundred times and nothing. I took it apart and cleaned everything in there carefully, including the two little holes. I carefully cleaned the piston bore, the piston, spring, rubber cap and rubber washer that goes around the piston. Re-assembled them according to the manual. It feels like there's no pressure at all building up in the piston bore. I fill the reservoir with brake fluid and absolutely none of it gets pumped out. Maybe the piston has worn away too much in the bore? There's nothing blocked. I've taken the thing apart and put it back together a dozen times. Is it time for a new front brake master cylinder? Any help at all would be greatly appreciated.
thx,
baz

 

Perhaps the rubber "piston ring/seal" was installed backwards?

 

Nope, the piston ring/seal is on there right. I put a mark on it with a Sharpie before taking it off and it checks out with manual. Is it possible the bore that the piston sits in is too worn? And I grasping at straws here but the rubber dust seal is not in great shape. I'm guessing that probably has nothing to do with it, right?
thx,
baz

 

If the Bore was pitted badly or had the build-up of foreign matter which forms from Aluminum Oxidation + Moisture ... the Seals might be losing pressure as they pass over the imperfection in the Bore.

The Master Cylinder on the 900 Pushes quite a lot of Fluid to handle the twin Calipers.
The Metal Plunger within the "Guts" of the Master has Fluid Metering Ports drilled through the Plunger.
There is also a thin, flat, Waved Washer which acts as an "Oil Lock Piece"
That Washer sometimes adheres to the Seal when the Seal is removed and it inadvertently discarded.
Check for the Washer.

Examine the Bore.
Hold it to light and look for imperfections.

The MOST Common mistake in rebuilding a Hydraulic Component is placing a Seal on the Plunger -- "Backwords"
The reversed Seal won't allow Pressure to develop.

 

I bought a used master cylinder on my 1100. Took it apart, cleaned everything. Reinstalled it and started pumping. I know I pumped it over a hundred times. I was patient and continued to bleed it out. Eventually I started getting a little air to bleed out. After about 15 minuted of pumping, the fluid started coming. Once the fluid started coming it bled great.. Great pressure.
You could try and "Gravity" bleed for a while. Fill the master and open both bleeders and wait..... Have a cup of coffee and tinker with somewhere else on the bike while you wait. Once the fluid starts leaking out the calipers. close them and try pumping.
Make sure the piston is returning all the way when you release the lever.
It sometimes takes longer than we expect to bleed brakes on a bike.

 

Thanks for the input folks. As for the bore, I wouldn't say it's badly pitted but it's not perfect either.

What caught my attention was Rick's mention of a - Waved Washer which acts as an "Oil Lock Piece" - Do you mean the black rubber washer that attaches to the top of the spring? There's also a circlip that holds the plunger or piston in the bore. Other than that, I'm not sure. Nothing else shows on the manual diagram.

And I checked again. The seal that goes around the plunger is on the right ways round. Actually, I just noticed that I can move the plunger side to side a tiny bit while its in the bore. That can't be good for building up pressure.

Also, I tried a gravity bleed. Tied the brake lever to the handle bar, opened the bleed screws - attached clear tubing running into empty jars. Left it like that all night. Nothing, no brake fluid running through.
Hmm... maybe it's time for a new MC.
Thanks for all the help.
baz

 

Try this:

Remove the MC brake line banjo completely. Fill the reservoir. Put you finger over the end of the threaded hole where the banjo was. Keep it tight against the hole and start pumping the lever. You may feel some pressure. With the lever against the bar, release the build-up of pressure by moving your finger a tiny bit (don't remove your finger completely). Repeat until you get squirts of brake fluid (need I say that you should be wearing protective gear?). Keep water handy to wash the inevitable spills. Once you have no bubbles, replace the banjo (quick as you can) and bleed the system as usual. Good luck

 

Bore is scored or pitted?
Metering Ports in Base of Plunger clogged?
Seals or Kit incorrect?
End Cup reversed or slipped or tilted?
Notch on Body for vent to atmosphere clogged; blocked?
Lever Pull Adjuster too far out to sufficiently move plunger?
Seals contaminated: Fluid in Brake Fluid Bottle NOT Brake Fluid?
(Yes. It's a longshot. But, I know it happens)

 

Thanks for the advice you guys. I'll try what you've both suggested and get back to you. Thanks again.
baz

 

Thanks for all the advice. I installed a master cylinder rebuild kit, seriously cleaned out the calipers, like Rick instructed, then bled out the brake lines like was advised and man O mannequins, have I got a set of front brakes now. Nice and tight at the lever, very progressive. It was such a hassle for so long, I can't thank you guys enough.
baz