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Bleeding front brakes

D

drewski

Training Wheels
Have replaced my front brake lines with Speigler Stainless - 2 lines.  1 line from MC to right caliper, and 1 from right caliper to left.  Also rebuilt the MC.  Tried to fill the MC last night and pump fluid through, and no fluid is being pumped down the lines.  There are little bubbles coming fron the 2 holes in the MC.  Also have speed bleeders, and thought they may be screwed up, so I removed the right one to try to get some flow, but nothing.  Is there some trick to getting the fluid going, or did I screw up something in the MC rebuild??
Thanks, Drew
 
Never heard of the two line setup from caliper to caliper but that doesn't mean it isn't correct. So you have both lines connected together at the right caliper connection? When I hear of two lines I alaways assume the two lines are connected at the mc. I would start with the line that comes from the master cylinder to the right caliper and disconnect it from the caliper and put the end in a jar to see if you have flow from mc to the end of that line with slight pressure applied to the brake lever (wear safety glasses). If you have good pressure there that sort of rules out the mc. Next I would connect the lines together at the right caliper and leave it off the left caliper and get the fluid throgh both lines and then attach it to the left and then bleed right and then left caliper. Are you sure the length of the line from right to left doesn't warrant two line setup at mc? Good luck.
 
Either way will work but caliper to caliper is going to be a little more difficult to bleed.

But anyway, what you need to do first is bleed the master. Ideally you would have a very short line from the master back to the reservoir. Then just slowly pump the lever until the bubbles are gone. Make sure the end of the line is in the fluid in the reservoir. You could cut an end off your old line and use that if you wanted just be sure it is thoroughly cleaned.

When that is done hook up the brake lines. Crack the banjo at the master and squeeze the lever, tighten the banjo before the lever is reaches the end of it's travel. then release the lever. Do this slow. Repeat until no air comes out. Make sure you keep fluid in the master. Then move to the caliper. repeat the procedure for the caliper connected directly to the master, then for the one on the other side, and you may have to go back and forth between all three points to get all the air out.

You may still have a spongy lever. So let the bike sit overnight, you might be able to get even more air out. I use a spring clamp on the lever to keep it pulled over night and that seems to help.
 
A couple of thoughts:


If you still have the stock bleeders, start bleeding with those, then final bleed with the speed bleeders. Because the air in the lines compresses, and there is so much air initially on new lines, there isn't enough pressure to move the check valve in the speed bleeder. 

I've found when installing the new brake lines, it helps to "prime" the lines by getting some brake fluid in the lines before bleeding. I actually used a small medicine dropper (syringe style) we got for the pets medicine (and no, I did not give it back for the pets  :eek: ). The goal is to get some fluid through, not try to fill up the hose, it obviously wont stay in while installing. Probably something to do about fluid surface tension.
I primed the lines before installing, it can be a little messy, then installed, bleed with the stockers, then switched the speed bleeders in.

If you have the equipment, with the stock bleeder screws, do a mityvac bleed to pull the fluid through.

Or, "pressure flush" the fluid up from the caliper stock bleed screw (be careful over filling the master cylinder, it will fill up QUICKLY! ) . I have done this with a large syringe, but you have to be careful.

And a final thought, tie back the brake lever, fill the master cylinder and leave overnight. That has been known to allow the air to come up through the master cylinder. Of course that won’t help with the hose going from caliper to caliper, the air will stay at the highest point in that hose, it will take pressure to purge the air from that hose.

EDIT: WillyP has some good advice also, he responded while I was typing  :)
 
Thanks Vic you reminded me of something else I do...

You might not want to do this as once you remove the piston from the caliper you'll need to thoroughly clean the caliper, and probably want to replace the seals too, but this will push all the air out quickly... Remove the second caliper, and remove the piston then fill the caliper with brake fluid. When you put the piston back in it will push all the air back up the line. Put it back on the bike and then do the first caliper. Do this with the bleeders and banjos tight. Leave the cover off the master. Cover the bike with rags and wrap rags around the master as it will squirt fluid out. Watch the fluid in the master you will probably have to remove some so it doesn't overflow.
 
:mad:Your on the right track. Those little bubbles are displaced by an equal volume of brake fluid. Do you get the idea it's going to take a long time.
As suggested I would try to prime the calipers first, then hook everything up and start with the right caliper bleeding it into a clear glass bottle
(not a brown beer bottle, you might forget what's in it) through a tube. Hold the bottle below or above the caliper and watch the bubbles as
you slowly pull the brake lever. I always put some grease on the speed bleeders threads to block any air from back bleeding into the caliper.
Once the right caliper has no bubbles remove the left caliper. move the brake pads back into the caliper as far as you can and put something
between the pads, (about a 1/4 inch) to keep the pistons in place. Once again with your tube and glass bottle in one hand hold the caliper
with the other hand as high as you can over the right caliper and with what's left slowly pump the brake lever. All this while keeping the MC filled.
That's one problem with this setup, you need four hands.
Good luck Richard
 
Bleed the master cylinder first. Vic or Willy gave you the proceedure already. If nothing is coming out of the master cylinder after you've bleed it then you have an issue with the rebuild.  I've always "pre-filled" my lines and calipers after any brake work. Sure fluid flows out of the lines while they are not attached, but they are now internally wet and it is easier to bleed them once they already have fluid through them. Something to do with capilary action I think, but it makes filling and bleeding easier.
 
Thanks for all the help guys.  I left the fluid in the MC last night, and the speed bleeders open several turns.  I came in from work tonight and the brake fluid was gone and a small puddle on the floor under right caliper.  I added some fluid. and it quickly started dripping out of the right caliper, and also the left caliper.  I was pretty surprised because the fluid had to travel from the right to left up over the height of the fender.  I closed the left caliper, and bled the right.  Closed the right, and bled the left.  Plenty of pressure, and the lever feels much better then before all this.  Too bad I ordered the regular bleeder valves to help fix the problem. (must have tossed the originals when I changed to Murph's speed bleeders.)
One last question about zip tying the brake handle overnight - MC cover on or off, or does it matter.
 
I've never understood this how zip tying the brake lever overnight would help. Once the brake lever moves just a bit it closes
the port from the master cylinder. All I think has happened is now the brake lines and caliper are under pressure. Do air
bubbles move easier under pressure? I do know they get smaller but as soon as the pressure is released they return to there
original size. Can someone explain how this helps?
 
RWulf said:
I've never understood this how zip tying the brake lever overnight would help. Once the brake lever moves just a bit it closes
the port from the master cylinder. All I think has happened is now the brake lines and caliper are under pressure. Do air
bubbles move easier under pressure? I do know they get smaller but as soon as the pressure is released they return to there
original size. Can someone explain how this helps?
Click to expand...

+1
 
I think with the pressure on the air may defuse into the oil over night.  The brake feels great in the morning.  By the end of the day the air bubble forms again and you are back to square 1.  No real help.
 
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