Yet Another Brake Bleeding Thread

[lakecountrydave]

I am having issues bleeding my front brakes. I have pressure, and the piston starts moving as soon as I start pulling the handle. However, I cannot seem to get all the air out of the system. The brakes stop the bike, but I can pull the lever to the bar.

I have a new master cylinder from parts and more, and I rebuilt my calipers. I have bled the master cylinder (3 times as I let it run empty twice ). I get it so no air bubbles are coming out, so I am assume that I am doing that properly. I have bleed the calipers until they are no longer releasing air bubbles. I have tried pulling the lever in and taping it that way over night. I have put a bunch of miles on it thinking that if air was stuck at the fitting behind the name plate that would dislodge them.

Currently, I have removed the calipers and tied them up so that they are the high point in the system. The left caliper seems to be leaking a small amount around the threads again. I have wrapped both sides in teflon tape three times, and after lots of bleeding the tape stops working. I also noticed that if I jiggle the handle bar for a while then pull the lever air bubbles will come up through the master cylinder. Although after a while they stopped. I have the lever taped half way to the bar again. Hoping for a miracle when I get up tomorrow.

What do you think I need to do to rectify the problem? I have pushed 3 large bottle of brake fluid through the lines using a mityvac.

[DGXSER]

Since you replaced the MC, is it the same size bore as the stock one? Hydraulics work on a volume and pressure basis. IF the bore on the new MC is smaller than the stock one, it will take more piston travel to push the same volume of fluid into the calipers. The volume pushed into the calipers is what develops the pressure to squeeze the pads together and stop the bike. JAT.

[crazy steve]

Could be several things going on here...

Beside the above-mentioned master cylinder size, did you install new pads? If so, until those are fully seated you can have 'soft' brakes. Did you check caliper/fork/rotor alignment? Again, this could contribute to the problem; don't assume that they're right, do check. If you're getting any leaks at the hose ends, teflon tape won't help; sealing is done by the copper crush washers. These work-harden in use, remove them and heat them red-hot, let them cool, and they'll seal much better.

I've had much better luck pulling fluid to/through the calipers when using my Mitivac. This is where you want to use teflon tape; apply the tape to the bleeders (so you won't suck air in around the threads) and power-bleed them. Easier to monitor master cylinder level this way...

Alignment procedure for the Special calipers here: http://www.xs11.com/forum/showthread.php?t=37207

[lakecountrydave]

The master cylinder that I got is smaller than stock 16mm vs 17.46mm. Other members had used this master, and reported good results. Although, I now realize that everyone that reported back also switched to stainless steel lines. Do you think that could be the issue instead of air in the lines? I do get pressure, but I can just pull the lever all the way to the bar.

I did install new pads, but I do not think that the new pads are an issue at this time. I say that because I went riding with my buddy on a 13 hour (riding, 15 hr total) shakedown ride.

I used the teflon tape on the bleeder screws, and I am using a mityvac. I did not consider the copper washers. My disk are centered in the brackets.

I will try heating the copper washers, reapplying the teflon tape to the bleeder screws and bleed the brakes again.

I did see mentioned in a thread that after using the mityvac that I would have to do a final bleed by hand. I have not done this, do I need to?

[DiverRay]

Yes, you WILL need to do a "final" bleed by hand. Also, the SS brake lines will make a HUGE difference if you are still using the old, stock rubber lines. I found a set from galfer for the front on the specials, at about $135 from pashnit.com. I'm not sure of the exact site, but a google should bring it up.

[crazy steve]

....Also, the SS brake lines will make a HUGE difference if you are still using the old, stock rubber lines...

+1 on that. I can nearly pull the brake lever to the bars with the stock parts, with that smaller bore master the rubber lines are the problem...

As to a 'final' hand bleed, I've found that you can't quite get all the air out of the front brakes with a Mitivac, but what's left will 'work' its way out after a few days without doing anything.

[Yard Dogg]

On my bike I had to reposition the master cylinder on my bar a couple of times to get the air bubbles out. I sat there for a good hour with the M/C in 2 different positions. 1st position (on side stand, bars turned to the left) to bring the bubbles up the line and out, second position (center stand, bars straight) for getting out any bubbles from the rear of the master cylinder. It helps to pull the lever back 1/2 way and let it flick back to give it a little jar and break the air bubbles loose. Was able to bleed them by hand that way. That's what they mean when they say the bubbles will work their way out. You will see tiny little bubbles coming up over and over again, then all of a sudden a large amount, then small, then more etc... It takes a while.

[Courtney]

Pressure Bleeder?

Has anyone used a pressure bleeder to pump the brake fluid UP the lines to the empty MC?? Just a thought, since I have one here taking up space, and I haven't bled the front brakes yet. I'm thinking that would push any air bubbles that might form up the lines? Then when the MC is full, I could pump the handle and that would seat the pads and push on the pistons. The level in the MC would drop and I could top it up. Sounds good, but the proof will be doing it.