Problem bleeding rear XJ900 brake- advice needed...

:?: Hey gang,
I've rebuilt the rear caliper with new seals, pads, etc, drained all that nasty old brake fluid. I filled the rear brake reservoir with new Dot 3 brake fluid, loosened the outside bleed nipple first (just like RickOmatic told me), attached clear plastic tubing that runs into a jar half full of brake fluid.
Then I started pumping on the brake pedal. The brake fluid in the reservoir didn't go down at all. I checked the brake hose running from the reservoir to the master cylinder and it's clear. I checked the hose running from the master cylinder to the rear caliper. It's clear too.
So I'm figuring that the master cylinder's not pumping the brake fluid but I'm not sure. There are no leaks anywhere. Anybody have an idea why the brake fluid's not getting pumped to the back brake?
Thanks in advance for any advice.
baz

 

I'd say the master cylinder doesn't want to take a prime by itself. My 750's fork mount master wouldn't prime by pumping, I had to get a long clear tube on a bleeder and suck on it. That worked. A vacuum pump would also work.

And I just joined the 900 club ! I won on E-Bay.

 

Or the bleeder screw is full of crud....and might be picking up crud from the piston reservoir area. Remove the bleeder screw and pump a couple of strokes and see what happens. Better yet, remove the hose from the caliper and let it "gravity bleed" itself overnight, and then try again with the bleeder screw. It takes an INCREDIBLY long amount of time to fill up what seems like tiny fluid lines with fluid if they've been fully drained. These tiny master cylinders just don't move much fluid, at all, on each stroke.

 

Take the Bleed Screw out and probe it for open and flow.
Leave it out and put your finger over the hole.

Have someone push down the Brake Lever and hold it down.
Remove finger from hole.
Place finger back on hole.

Release Brake Lever.
Push the Brake Lever down and hold it down letting fluid out of the caliper.
Plug the hole when you release the lever.

If the Master isn't sending fluid down the line pushing out from where you are holding the Bleed Screw Hole ... you need new seals in the Rear Brake Master.

 

Thanks for all the advice. I appreciate the help. I'll try what was suggested and report back on how it all turned out.
thx,
baz

PS- TIMEtoRIDE: Congrats on joining the 900 club.

 

Well, it looks like the Rear Master Cylinder needs a rebuild. The rubber seal at the plunger rod on the bottom has a spring built into it. That spring had torn through the rubber. Once I got the rubber seal off, it was all crusty old brake fluid and thick rust inside the lower master cylinder.
But here's the thing. THIS rear master cylinder isn't the same as the one shown in the factory shop manual. The one on the bike is quite different. The bottom plunger that attaches to the brake pedal hinge, it has a bullet type end on it that inserts into the bottom of the master cylinder. This bullet end moves up into a bowl shaped cavity. I can't tell how that gets the brake fluid to pump up to the brake line that attaches near the top of the master cylinder. There don't seem to be any holes in this bowl shaped cavity going to the upper master cylinder.
If anyone knows what I'm talking about and can explain it to me, I'd be most obliged.

 

Baz... A picture says a thousand words... Got a camera?

 

Well, I've take a couple of pics...

In the first pic: Bottom view of the rear master cylinder body. You can sort of see the inside which is a bowl shaped cavity. At the bottom right is the plunger that fits into the cavity. The other end of the plunger is a threaded rod which attaches to the rear brake pedal pivot. To the mid-right in the first photo is the rubber cap that fits over the plunger and is meant to keep moisture and dirt out of the bowl cavity. What I don't get is what all this does. The bowl cavity doesn't seem to move in anyway. This might sound dumb, but how does the plunger pump brake fluid up to the brake line going to the rear caliper?

The second photo is the side view of the rear master cylinder. On the right is the opening where brake fluid comes down from the reservoir. The round opening at the top is where the brake line going to the rear caliper hooks up. Inside the opening is what appears to be a threaded rod.
As I said, I don't understand how the rear brake pedal pivot pumps brake fluid to this opening. Also, after reassembling, it still doesn't send brake fluid to the rear caliper.
Thanks in advance for any help.
baz

 

Gravity bleed overnight?

I’m puzzled…I would have thought the fluid would ooze out of the hose in a matter of minutes leaving a whole lotta air in the system?

My system is pumping but the lever continues to bottom out despite many repetitions…air bubbles continue in the clear bleeder hose relentlessly

 

Use a vacuum pump £15 off flea Bay job done

 

I've done lots of car brake/rotors before, but I'm a noob to bleeding brakes on a bike, but I'll add that my buddy loaned me a vacuum bleeder that hooks up to a compressor. Wow, it was like magic. Only thing is there is a tad bit of momentum to it so even when you shut it off, some more fluid might flow so keep ahead of the reservoir level.
Piston on my 85 xj650 was pitted and piston needed replacing as part of the caliper rebuild. I just helped a friend with n old 80's KZ1000 and caliper was similar, pitted and needed rebuilding, brake lines etc.