Front brake caliper will not "pressurize" ...


XS650 Enthusiast
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Norfolk, VA.
So I'm trying to get my front brake system bled, and I cannot get the pressure built up in the system to get the caliper to compress. I bought a brand new master cylinder, new braided lines, new pads, cleaned out the stock hose junction block, and rebuilt the old caliper. (1979 single front set up)

I seem to have the air out of the system, and I'm getting brake fluid through the line all the way to the down to the caliper, and out of the bleeder. Short of taking the caliper off and going through it again, am I missing something here?!?!

This is the last thing holding me up from getting the bike on the rode, I've been working non-stop for three months now and would love to take her for a test ride to see if I need to work on anything else before it's good to go!

As always, thanks in advance for any advice you might have ...
I have better luck cycling the lever rapidly in half strokes to get some pressure to build with a completely dry system. Once you get it going it's business as usual. I do usually break all the banjo fittings open with pressure in the line to "burp" them out. Sometimes they trap air that won't push out. Normally an issue if they are hollow ground inside, which many are. The My-T-Vac works good if you have one or want to buy one. Your hose connection to the bleeder must be pretty much flawless for it to work it's best though.
Just some of the usual stuff;
1- try to keep the master cylinder as level as possible, usually means bars are turned to the left
2- keep fluid level up and never below 1/4" from the bottom of the reservoir
3- with the lever squeezed, applying brake, just crack open the banjo bolt at the master cylinder, gets rid of air at the joint, when lever moves into the bar, re-tighten banjo bolt
4- continue down the brake line doing each connection point or banjo bolt. Air in these causes lots of problems.
5- hose on bleeder into can that rises up from the bleeder, so brake fluid is being forced up hill and you can see air bubbles in the line if they exist.
6- then it's the usual, squeeze, open bleeder, close bleeder, re-squeeze open/close bleeder until no air bubbles.

Looks like jd750ace and I were typing at the same time and working from the same book of memories.:laugh:
JD if you keep beating your head like that, you are going to have brain damage.:laugh:
Unless I missed others post, got the lines bled both front and back but still have no pressure on the pedal or lever which is not moving the caliber. Yes they both have disc in them Front Caliber is a new one from Mike's XS along with new Magura reservoir and lever and new braided hoses front and back. A new Rear Mater cylinder from Mike's XS which would not pump fluid no matter what I did to it. Rebuilt the old master with the parts from the new master !! But still can't get pressure....lines are bled and air free...any ideas?
It's hard to imagine both master cylinders are assembled wrong, but search here for brake posts because I'm sure one showed the assembly of rubbers and springs installed on the piston before assembly.

Air in the system can be hard to remove and it doesn't take much to ruin a good brake job.

Follow the steps above and be sure the bleeder and hose are a good fit so you can detect air in the system and don't introduce more each time you bleed.

Two people works better. As the hose/bleeder and wrench are easily dislodged as you probably already know.

It's important to pull in the lever, then just crack open the bleeder and as soon as you feel the pressure at the lever disappear or the lever reaches the bar, re-tighten the bleeder. This avoids getting air back into the system. Then repeat.

Stay with it, it will come.

If you do have all the air out and there's no pressrure something would have to be broken, but just in case...there won't be any pressure if you haven't tightened the bleeder screw or if the pads aren't against the rotor yet.

On mine there's a tiny hole that can develop a bubble in the mouth that keeps fluid from going past. After I pop the bubble a few times with a sliver of wire it works ok. There are probably two holes, one for return and one for fluid to go down. There are many ways to get this done but I've never had to use any pumps, etc. If one way isn't working try another for a few minutes.
Don't start with brake lines that are empty. That just means you have a whole lot of air to get rid of.

Start with the new lines on the bench. Use a syringe to pre-fill the brake lines. Make a "U" shape of the line..............fill from one end until fluid comes out the other end. Pre-fill the caliper as well. Carefully keep the line in a "U" and connect the lower end to the caliper. Raise the line up and connect the upper end to the master cylinder. Fill the master cylinder.

Bleeding now takes just a couple of minutes, because there is almost no air to bleed. Very simple and has worked well for me.
I had nothing but bad luck with those after market handlebar Cyl until after the third one I bought I figured it out. They would just not bleed down to the puck. Found that the handle was not the right one for the master. Took it off pushed the plunger in by hand and in 5 mins had break. Had to sand down handle because it was too fat and kept plunger open just enough to suck air. Now I buy from others too much work for brand new parts.
Sometimes, when all else has failed, I've had success by wrapping the bleeder threads with Teflon tape. The bleeder threads can allow air to enter while bleeding due to a siphon effect (I think). Be sure not to cover lower portion of bleeder.



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Well gentlemen, I cracked loose all of the banjo's starting from top to bottom, made sure that my bleed hose was fitting very snug, and kept repeating the process ... squeeze, bleed, squeeze, bleed, etc. All what do you know, the brake works like a champ, and my very first test ride was a complete success!

Thanks for all of the advice, I love this forum! :bike:
I have found that an empty Master won't bleed well unless you bleed just the master. I do this by leaving the line off. Put my finger tip over the hole the line hooks to. Now pump the lever slowly. As the plunger pushes the fluid, it comes out around your finger tip. As you release the lever your finger tip seals the hole so fluid gets drawn from the reservoir. Once you get a good flow of fluid out past your finger connect the line.
Hold the end of your line the same way as you did the master. So your finger tips seal. Now bleed the line. Attach to the next thing in line. A junction or the caliper, Once you get all the lines and such bleed at the caliper.
Filling the lines as RG suggested will speed up the process.