XJ650J - Need Help Bleeding Brake on a Total Rebuild

I finally got around to totally rebuilding the front disc on my XJ650J. I replaced the lines, rebuilt the master cylinder and caliper, new pads, etc., etc. I buttoned everything with no leaks but am now having a problem bleeding the system. Despite many, many cycles, I'm still not seeing any fluid from the bleeder screw and the master cylinder reservoir is still pretty much full. I just see a bubble or two in the recovery jar about every other attempt. I even borrowed my friend's hand-held pressure bleeder but that hasn't faired any better - still no sign of fluid and the reservoir remains full.

I've bleed the brakes many times on cars but this is my first attempt on a bike so maybe I'm missing something. Are you suppose to bench bleed the master cylinder somehow before you install it? Do I have some kind of vapor lock? I left the master cylinder cover off and didn't really notice any "movement" in the fluid when I applied the brake. I would also think I should see more pressure at the bleed screw apart from the occasional bubbles.

Did I screw something up? I'd hate to start pulling things apart again (and investing in a new set of copper crush washers) if I don't have to.

Help / Thanks!

 

... "still no sign of fluid" ??

Something's not open or seriously plugged-up.

A Vacuum Bleeder will suck the Air out and all the Fluid too.

The System may have NO AIR in it and still not pump-up if the Master Cylinder has failed.
The Master needs to be capable of producing and sustaining Hydraulic Pressure.

If the MC won't "Pump" ... bleeding the Brakes if futile.

 

... "still no sign of fluid" ??

Something's not open or seriously plugged-up.

A Vacuum Bleeder will suck the Air out and all the Fluid you put in and not be successful if the MC's bad.

The System may have NO AIR in it and still not pump-up if the Master Cylinder has failed.
The Master needs to be capable of producing and sustaining Hydraulic Pressure.

If the MC won't "Pump" ... bleeding the Brakes if futile.

 

http://www.xjbikes.com/Forums/viewtopic ... rakes.html

 

Okay, if I hear you guys correctly, sounds like since I was NOT able to pull the fluid from the MC with the pressure bleeder there must be a blockage somewhere. I had pull teflon tape on the bleeder screw so I'll check that first. If that looks okay I'll pull the MC to see what is going on.

More to come....

Thanks for helping me thru this most difficult time. I've been working on this bike all summer and this is the last step before she becomes road worthy..

Cheers!

 

It took me several hours to bleed the twin calipers on my xj650 after a full rebuild. A motorcycle master cylinder piston only moves a tiny volume of fluid in comparison to an automobile. The most effective method I have found is to attach a long length of clear plastic tube to the bleed nipple and suck as hard as you can before opening the bleed nipple and squeezing the lever. This produces a vacuum in the plastic tube and draws the fluid through a little each time. After repeating this process dozens of times I finally achieved a pressurized system. To finish off, tie the lever as close to the handlebar as possible and leave overnight. You will be rewarded with a much firmer feel the next day.

 

I think I'm doing the same basic "suck" technique with my friends pressure bleeder - I created a vacuum with the pump (10 - 15 inhg) and then slowly open the bleeder screw. I never applied the brake however. I thought that would just close off the return to the MC reservoir....

I expected this process to be slow and painful but the fact that I'm not seeing any fluid drop in the MC seems to indicate I have a problem somewhere...

Really appreciate all the replies!

 

I suspect the master cylinder body may have a plugged orifice or two.

Everything else is huge and primitive. You did replace all of the junction/banjo bolts, right? No chance of a corroded-shut passage in a banjo bolt?

 

Are the 650 brake lines straight from the MC or do they go through a brake fluid "tree" on the upper part of the forks under/in behind the headlight?

At first, if the calipers are completely empty, you might just want to sit there with the bleeder valve open and pump away on the MC for a bit until you get some fluid moving. Gravity will help here and keep it all from being sucked back up into the MC. You will have a little more work on the end getting all the air out, but this should at least prime the system and get you going.

It does sound a little bit like you installed the plunger on the MC backwards.
Best of Luck

 

Another common place to plug up is the bleed screw itself.

 

you said that you put Teflon tape on the bleed screw... be sure you didn't cover up the hole

 

Hey 3BadBirds,
Did you get to the bottom of your bleeding problem?

 

Thanks to everyone for their help!!!

The problem turned out to be that the second smaller port in the MC wasn't clear. Not sure how I missed it but once it was clear she bled like a champ.

Just as a FYI, I used a cheap pressure bleeder from Harbor Freight that I had read mixed reviews on. In my case, it worked great and the system was bled in a matter of minutes. I guess I finally got lucky.

Just curious, I've seem some really cheap complete MC units on eBag for under $30 - about what I paid for a rebuild kit. One of them even came with a light switch and extra piston assembly. Sounds awful cheap. Anyone have any experience with them?

Thanks again for the help and encouragement.

Cheers!

 

Awesome!

I have a cheap HF pressure bleeder too. it gets used maybe 5 times a year between the cars, bike, + friends borrowing it.... totally worth it!

I'd buy a better one if I was running a shop or something.... but for occasional use, I've never went wrong with HF.

 

You just have to be prepared to spend some time getting the jar to seal. Even out of the box mine leaked. I ended up using some teflon tape......

Cheers!