MityVac Operation

[mglowe]

My two years are up and I want to replace the brake fluid. I saw Writeme43's howto and thought a MityVac would be neat to have (I love gadgets too) so ordered one. Now here is where it gets ugly...

I hooked up the MityVac and pulled a vacuum but the very second I opened the bleeder screw - bubbles. I mean bubbles everywhere at the fitting. What is going on here? There is a tight seal around the hose and fitting, as I see it, so maybe the air is coming from around the screw threads?

I know it's not coming from an existing condition - my brakes were fine before. It's obviously I don't what I'm doing with this gadget so I simply went with the old method of bleeding brakes. I thought in its operation I could open the bleed screw and brake fluid would siphon out, as long as a vacuum existed, and I could add fluid all in one shot (never touching the brake lever). Am I wrong or have I missed something entirely?

 

[Hellgate]

They can be tricky. 1) Try turning the bleed valve less. 2) Wrap plumber's tape around the base of the bleed valve. This will usually prevent the air from going back in. 3) If all else fails buy a pair of speed bleed valve. They have a ball to prevent the air from going back in. Like: http://www.spieglerusa.com/cfm/bleeder.cfm

When I install my Galfers bleeding the brakes was a total PITA. I've l bleed many bikes and cars and the FZ was the worst.

 

[nlheikki]

I had the very same issue. All I did to fix it was loosen the bleeder screw a little extra and the fluid was flowing with no air bubbles at all.

-Nick-

 

[Fred]

+1 to Pete's suggestions for the Mity-Vac. The bubbles you're getting are from air flowing past the threads.

EDIT: You did have the cap off of the brake fluid reservoir, right?

I've used a Mity-Vac, but frankly, I find it easier to bleed the brakes using the conventional method. It's faster, simpler and more effective.

Here's the method I've worked up over the years. Some of this is taken from the advice of others, and some is my own invention (the lever twitch method). It's based on the fact that air in the brake system doesn't want to go down. It wants to go up, so that's what you should encourage it to do.

First, bleed the brakes until you're getting brake fluid from the bleeder nipple. Then close the nipple and move on to this technique.


Step 1. Use the plastic handle of a screwdriver and tap on the caliper all over it. Do the same on the brake line and all fittings, starting at the bottom and working your way to the top. This will dislodge any air bubbles that are stuck to the walls of the caliper or hose.

Step 2. Tilt the motorcycle and handlebars so that the master cylinder's bore is angled down to the left (viewed as you sit on the bike) The idea here is that the piston end of the master cylinder should be the highest point.

Step 3. Twitch the brake lever. Don't squeeze it, just give it the slightest movement. You should see air bubbles come up through one of the two holes in the bottom of the reservoir. Release the lever and repeat the twitch. Keep doing this until you get no more bubbles. You have now gotten all the air bubbles out of the master cylinder.

Step 4. Bleed the caliper just a touch more to get rid of any remaining bubbles down there.

Step 5. Bleed each banjo fitting. To do this, slightly loosen the fitting while squeezing the lever. Once some fluid leaks out of the fitting, tighten it. Then release the lever. This will get rid of any trapped air in these fittings. Do the bottom ones first and work your way up. Before you do each fitting, tap the hoses below it with the screwdriver again to keep those air bubbles moving up and out of the system.

Step 6. After you've bled the last banjo fitting, do the lever twitch trick again. You may clear a few more small bubbles out of the master cylinder.

Step 7. Do a final quick bleed at the calipers to make sure that there's no air bubbles left in them.

At this point, your brakes should be very firm and functional. If they're not, then something else is wrong.

Also, if you ever replace a master cylinder, you can avoid all the bleeding by keeping the brake hose held vertical, and using the lever twitch and banjo bleed methods to just bleed the top end of the brake system once it's all back together. It's a real timesaver since it lets you bleed your brakes with minimal tools.

 

[jeff in ohio]

put one to two wraps of plumbing tape around the bleeders and screw them back in. This will stop the leaks. Also, when installing new lines, I have always found one of these to work best since sometime you get an airlock and the mighty vac just want do it. get one of these....

http://www.denniskirk.com/jsp/produ...ain&catId=&productId=p28293&leafCatId=&mmyId=

then with some t fittings and line from a auto parts or harware store, you can hook this beauty up to both calipers and force fluid back up thru the system to the master cylinder. jsut make sure you do not overflow the master.....

 

[ddg]

For just bleeding the brakes I think speedbleeders are the way to go. While refilling the system (brake line change), a mityvac works very good to get the process started but I think I would then use the speedbleeders to finish it off.

 

[mglowe]

Thanks to all who responded - great advise. I'm also thinking the next time I go at it I just might go visit Nick as he is closer.

 

[wrightme43]

Hey great ideas here.

Would you mind posting a how to "twitch bleed" brakes thread with photos when you get a chance? It would be good in the how to area. I have never heard of it, but there is just lots I dont know. LOL

 

[nlheikki]

Thanks to all who responded - great advise. I'm also thinking the next time I go at it I just might go visit Nick as he is closer.

Just give me a heads up if you're in the area.

-Nick-