Brake bleeding headaches

[Skinner]

1982 GSX750S Katana - dual front discs, anti-dive forks.

I dismantled, cleaned and re-built the entire system over the winter. All rubber seals are new, brake lines are new SS braided, speed bleeders (with teflon tape), new OEM master cylinder piston/cup set, new OEM master cylinder cap seal.

Because of the anti-dive each side has 2 bleeders - one on the caliper, the other on the anti-dive. The manual states that bleeding should start with the anti-dive then the caliper, which I did for both sides. I wasn't happy with the results from bleeding the standard way so I purchased a vacuum bleeder kit. This worked well and seemed to suck out all of the air bubbles. However, I still had a mushy brake lever. So I proceeded to wrap the lever tight to the throttle and leave it for 12-24 hours. This did firm up the lever but not enough, so I did it again 3 or 4 times, but still have a mushy lever.

I've vacuum bled the crap out of the system and have gone through quite a bit of brake fluid as a result. To me there is obviously still some air trapped somewhere in the system but I'll be damned if I know how to get it out. Can anyone offer any tips or suggestions? Is there anything I'm doing wrong? Could it be the speed bleeders? They've worked well for me in the past without teflon tape, but I added it just to be sure.

This is the last item on my to-do list before I road test and get the safety inspection done, so I'm anxious to get the brakes working properly.

K

[Nessism]

Did you rebuild the calipers and if so did you use K&L seals?

[Skinner]

Did you rebuild the calipers and if so did you use K&L seals?

Hi Ed,

The calipers were disassembled and cleaned. I did not replace the seals because they were in good condition. That said, I can't way whether or not they were OEM to begin with. I did replace the rubber boots on each front caliper with OEM's.

[Sandy]

Sometimes depending on hose and banjo configuration I've had some air stuck inside the banjo bolt area, vacuum bleeder should have gotten it all but who knows. Try gentle pressure on the lever as you just slightly crack open the banjo bolts one at a time until you see a bit of fluid come out then tighten. Wrap a cloth around them because if there is a bit air they'll spurt a bit, if the fluid just sort of oozes out there was no air trapped. Might help, might not but only takes a few minutes.

[Skinner]

Sometimes depending on hose and banjo configuration I've had some air stuck inside the banjo bolt area, vacuum bleeder should have gotten it all but who knows. Try gentle pressure on the lever as you just slightly crack open the banjo bolts one at a time until you see a bit of fluid come out then tighten. Wrap a cloth around them because if there is a bit air they'll spurt a bit, if the fluid just sort of oozes out there was no air trapped. Might help, might not but only takes a few minutes.

Thanks, I'll check this.

[mmattockx]

To me there is obviously still some air trapped somewhere in the system but I'll be damned if I know how to get it out. Can anyone offer any tips or suggestions? Is there anything I'm doing wrong?

If the banjo bolt into the master cylinder is pointing upward this makes it the high point in the system and it will sometimes trap air. Try cracking it under pressure as Sandy describes below.

Try gentle pressure on the lever as you just slightly crack open the banjo bolts one at a time until you see a bit of fluid come out then tighten.

+1. I have had banjo bolts trap air as well. OP, don't forget to re-torque all your banjo bolts once you have gone through them clearing the air bubbles.


Mark

[bwringer]

Who's Blake and why is he bleeding?

You might need to bench bleed the master cylinder.

Since it's already mounted, you don't need a bench or vise -- remove the lever and carefully push the piston all the way in with something blunt. You may need to use a rag or towel and crack the banjo bolt open a little.

This often gets that last damn bubble of air in the master cylinder to burp up.