newly rebuilt front brakes, no pressure

[Guest]

I rebuilt the brakes, replaced pads, replaced caliper seals, replaced brake lines with Stainless lines, rebuilt the master cyl.

bled with no air bubbles left on either side, still no pressure. Rear brakes are grabbing well though.

could this be a bad master cyl kit, it seems to jet a little fluid back up through the reservoir. Or did I maybe just do it wrong?

heres the video instructions I used to do it. https://www.youtube.com/watch?v=6YSldW85ioI

[chuck hahn]

#2 The spring goes in. Then the rubber cup with the "bowl side" facing the banjo bolt end. Then the flat brass washer and then the piston. The little jetting coming up ism the return port and thats normal.

[chuck hahn]

Be sure the fittings are tight and no leaking crush washers.

Bleed the left side first as it is the farthest distance of line away from the master.

Bleed the right side.

Go back and rebleed both of them again to be sure all air is out.

Tie back the lever tight to the bars over night with a bungee cord once you get pressure on the system.

[shameless]

Tie back the lever tight to the bars over night with a bungee cord once you get pressure on the system.

I'll do that, but what does that do? (Never done this before)

[chuck hahn]

Darned if I know just how it works, but by tying it back over night the entire system ..just by some unknown to me magic.. will be like the best brakes youve ever felt on a bike. super solid lever and just an touch with the fingers and they are stopping you.

Pump up the rears and wedge a hammer handle between the frame and the arm to keep the pedal depressed and dont jump on the brakes after that. press with your toe.

[sinkankan]

You can get a 100cc syringe from most auto shops and a clear piece of 3mm ID tube, loosen the nipple and compress the syringe. Put the hose on and draw the syringe back, it'll pull out any nasty air bubbles. You may have to try this on both callipers twice.
If you're using a bottle try putting the bottle under the level of the nipple, (hanging down) this worked for me doing my GS850.
good luck.

[bwringer]

Many people don't realize you have to bench bleed the master cylinder.

You can leave it on the handlebar, or use a padded vise. Either way, make sure it's close to level.

Wrap a rag around everything to catch the brake fluid.

Remove the brake lever.

Remove the banjo bolt.

Remove the master cylinder reservoir cap.

Insert a tight-fitting piece of plastic tubing -- ideally, you have a size on hand that will sort of catch the threads. This is only for a minute or two and doesn't need to be all that perfect.

Hold the other end of the tubing so it's in the reservoir.

Use something blunt -- a wooden stick, perhaps an Philips screwdriver if you're careful not to slip and scratch the bore -- and slowly push the piston ALL the way in and out. A couple of seconds per stroke is sufficient so it doesn't squirt you in the eye. (Basically, the lever can't push the piston all the way in, so you have to use a stick to do it to get the last few bubbles when you're starting with a dry master cylinder or a fresh rebuild.)

Marvel as a few wee bubbles burp out at the end of each stroke.

Keep going until no more wee bubbles burp out of the depths of the master cylinder. Sometimes you can "jiggle" the piston right at the end of the stroke to get those last few bubbles.

Remove the hose, reattach the brake line and bleed as usual.


Tying the brake lever overnight does the same thing, but more slowly -- when the piston first starts to move, it uncovers the relief port (that teensy hole). Tying the lever allows the bubbles to rise to the top and work their way out naturally over a few hours.



The other issue that pops up sometimes is tight seals in the calipers following a rebuild. The seals retract the pistons a bit when you let go of the brake lever, and never contact the rotor. To overcome this, once you've gotten everything bled, operate the brake lever very rapidly so the seals don't have a chance to retract the caliper pistons with each stroke. This will usually get the caliper pistons moving and in position.


When properly bled and with stainless lines and decent brake pads, GS disk brakes work surprisingly well.

[shameless]

Heres what ive been using... I have a shop vac. Attached to a piece of oxygen tubing, (it was readily available,) into the lid of a mason jar, then another piece of oxygen tube ran from the bottom of the mason jar, up through the lid, and to the bleeder screw. Works ok, nice long tubing to make sure of no bubbles.

[chuck hahn]

Not with a Mighty Vac Brian. Maybe just wiggle the lever a tad at first to get the fluid moving. and they make a pneumatic one that you hook to your air hose. Ive never had to prime a master cylinder ever.

Secondly..If hes getting fluid in the jar with his setup and the levels going down in the resivoir the master cylinder is primed by virtue of the fluid being sucked past the cups. And he states lots of line and no bubbles..so that tells ( me at least ) that hes got fluid in the entire system and still no discernable pressure. I would check that the innerds are in the master cylinder correctly and retry it.

http://mityvac.com/

http://www.harborfreight.com/brake-fluid-bleeder-92924.html