ANOTHER brake question

Well, I got everything put back together for the front brakes. Bled the system and have no air bubbles.

Here's how I *understand* the brakes work:
You squeeze the handle and that pushes the MC piston in. This creates pressure that pushes the caliper piston out...just like car brakes. When you release the handle, the spring in the MC and the handle return spring push back, fluid draws back into the MC, and pulls the caliper piston back in.

With that in mind, here's my trouble. When I put everything back together, of course, the piston was all the way into the caliper so that I could fit the new pads around the rotor. After I got all the air out of the system, I can't get the piston to stay out and go further out. What the piston does is come out like it's closing the brakes, and when I release the handle, it draws the piston back in.

Did I put the master cylinder together wrong? I followed the instructions to a T. Is there something else that I'm just not doing? I've searched, and there are lots of instructions on bleeding, but nothing adressing how to get the piston to continue to push outwards with every lever pull until it's seated tightly.

 

try pumping the handle first. it ALWAYS takes a few pulls to pump the brakes back up. just like a car.

the piston only moves so far. it doesn't happen all at once.

 

I understand that part...maybe I'm just being impatient? I have pulled and released the handle a BUNCH of times. Does it just take a bunch more??

 

maybe you haven't got all the air out then.

the easiest way for me is to use a vacuum pump at the caliper bleeder and suck the fluid through the bleeder.

others have different ways that work good for them.

motorcycles are a PITA when it comes to bleeding.

 

nothing pulls the caliper piston back, the pressure is just taken away
the mc springs return the lever and draw more fluid in if it needs it
what your seeing is most likely the seal flexing
you still have a lot of air in it

 

*sigh* I like car brakes better. Is there any way to tell, or does it make a difference, if that air is in the line or the caliper? Or do I just keep bleeding until I've cycled a bottle's worth of fluid in my catch jar?

 

doesn't matter if there's air in the line or the caliper. it still has to go through the caliper to come out the bleeder. to do a thorough job. and there's no way to tell where the air is.

i wouldn't try bleeding from one of the banjo fittings either.

if youi don't have a vacuum pump. autozone rents them for free.

 

it don't matter where it is, first turn the wheel to try to get the line to give any air a path up to the mc (a bubble won't go down by itself)
take of the mc lid, cover the tank with plastic just in case, in the mc there are 2 holes big and small now slowly squeeze the lever, hold it 1 sec, then let it snap back
you should get bubbles from the small hole
if you squeeze the lever fast it might push the bubbles down the line
if you try to bleed like a car, any time your not pushing the fluid down, the bubble is going back up

 

The only way I was able to purge all the air outta mine, after a lot of frustration, was to remove the bleeder screw completely, push my thumb over the hole tightly, and pump the lever like there's no tomorrow, being careful of course to not bottom it out, which can damage the MC....

You feel air spitting past your thumb until eventually the fluid makes its appearance, once it's flowing well put the bleeder back in, do a couple of open/close standard bleed strokes, and it should be good. Obviously don't let the MC go dry during this, or you're back to square one.

Also...calipers have what's called a stroking seal that pulls and slightly retracts the piston after application, in order to reduce parasitic brake drag...but that's not what you're seeing, you just have air...

P.S...some bikes have an issue where the brake hose outta the MC arcs upwards and goes higher than the reservoir, which creates a problem, you have to loosen the MC and move it to a spot on the bar that puts it at the top...not really an issue with XJ's with stock bars though, I think. Just in case you run into this at some point in the future...

 

Make sure the small hole in your MC isn't blocked

 

The Maxims trap air at the banjo bolt on the master cylinder.

Wrap the area where the banjo bolt is with a paper towel. Squeeze the lever. Crack the banjo bolt then tighten it up. Release the lever.

Repeat until you get a good flow of fluid out the joint.