Brake Bleeding - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 14 (permalink) Old 05-12-2015, 07:26 PM Thread Starter
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Brake Bleeding

I installed the dual SS lines for the front calipers. I bled them with a mighty vac hand pump. However they were very spongy. So I rebled them. I get a lot of air bubbles on the right one. Filled the vac reservoir 2 times but still get bubbles. The left side has no bubbles. Once vac is produced it pulls fluid and no bubbles. Is there a trick to blkeeding them? I do not have any leaks so I do not think the left side is pulling air from anywhere outside the system. Any ideas?
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post #2 of 14 (permalink) Old 05-12-2015, 08:35 PM
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Do you have a bleed nipple on the master cylinder? If so, have you bled there?

Make sure the reservoir never gets empty - keep topping it up. You can apply vacuum, then also pump the brake lever. Once you have a little lever pressure, close the bleed nipple whilst holding the lever, then pump to get maximim pressure, then release the bleed nipple whilst still holding the lever & not letting off till you have closed the nipple. Repeat again & again till you get a constant normal brake feel, even after releasing for some time.

Finally, once the lever travel doesn't really change from pumping with the bleed valve fully slosed, get a good cable tie and keep the lever applying plenty of lever pressure overnight. It'll help get rid of any small bubbles. You can also flick the lines to help dislodge any tiny air bubbles.

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Last edited by The Stig; 05-13-2015 at 09:29 AM.
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post #3 of 14 (permalink) Old 05-12-2015, 09:27 PM Thread Starter
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I don't think I have one on the master cylinder. I'll double check tomorrow as well as doing the zip tie thing. Thanks again.
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post #4 of 14 (permalink) Old 05-13-2015, 06:13 AM
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The bubbles may be coming from where the vacuum line attaches to the nipple on the caliper. I had the same problem with a vacuum bleeder, it turned out that, for the device to work, the nipple had to be turned far enough out of the caliper that it would pull air from around the threads. Took me the better part of a day (and a helluva lotta brake fluid) to figure it out. At least the brake lines got thoroughly flushed.

Since then I've stopped using vacuum bleeders, I just use the old fashioned way. Hydraulic brakes use positive pressure to work, bleeding them with the same positive pressure is generally good practice. A motorcycle is easy to to by hand anyway.

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post #5 of 14 (permalink) Old 05-13-2015, 07:50 AM
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Quote:
Originally Posted by BTF/PTM View Post
The bubbles may be coming from where the vacuum line attaches to the nipple on the caliper. I had the same problem with a vacuum bleeder, it turned out that, for the device to work, the nipple had to be turned far enough out of the caliper that it would pull air from around the threads. Took me the better part of a day (and a helluva lotta brake fluid) to figure it out. At least the brake lines got thoroughly flushed.

Since then I've stopped using vacuum bleeders, I just use the old fashioned way. Hydraulic brakes use positive pressure to work, bleeding them with the same positive pressure is generally good practice. A motorcycle is easy to to by hand anyway.
It's true air can be sucked through the threads, or the rubber nipple fitting. This is why I suggested also using pressure from the m/c. That way you're not just using vacuum.
There's a better way to bleed and that's using air pressure on the reservoir to force the fluid through the lines & out of the caliper. Unfortunately bike reservoirs are too small in capacity, but it works very well on car brake systems.

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post #6 of 14 (permalink) Old 05-13-2015, 09:19 AM
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Easy way to defeat the air leak by the threads on the bleeder screw is to use a little plumbers tape. Pull the bleeder screw out, put your thumb over the hole in the caliper. Use your other two thumbs (and fingers) and put a couple of wraps around the threads. I've done this on about 1/2 dozen different vehicles (including bikes) and it allows the MityVac to work Great. It seems to last as well, I've never had to apply more tape on successive bleeds.

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post #7 of 14 (permalink) Old 05-13-2015, 09:26 AM
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Nice - I like your thinking Dave. Simple & effective. Thanks!

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post #8 of 14 (permalink) Old 05-13-2015, 11:43 AM
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We've got Mity-Vac's and pneumatic vacuum bleeders here at the shop and while they are great for complete fluid swaps I can physically bleed the lines by hand in way less time than it takes to just get one of the vacuum set-ups out of the cabinet and set-up and it also eliminates the possibility additional problems from the vacuum itself or the aforementioned leaks from the bleed nipples as you are manually opening and closing them yourself.
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post #9 of 14 (permalink) Old 05-13-2015, 12:04 PM Thread Starter
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Thanks for all the advice guys. I'll do the Teflon tape as well as bleed by hand. I have a feeling I'll have good breaks by this afternoon!
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post #10 of 14 (permalink) Old 05-14-2015, 05:39 AM
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There's a gadget called a speed bleeder, too, that seems like a cool idea. They've been around for ages, numerous companies produce them. Anyone here have feedback on them?

2006 Black Edition SP2
- Stickerless black...giggity
- Assorted stone chips
- Multicolor bug splats, updated weekly
- Custom boot scratches and crash marks on the tailpiece
- Scuffed bar weights & brake lever from asphalt acrobatics
- Road grime under the fender and tail
- Leo Vince exhaust
- Otherwise OEM, not gonna make BOTY any time soon


HOE-LEE SHEE-YIT, the TORQUE!!!
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