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Old 06-10-2002, 08:31 PM
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Post Bleeding Brakes with a Mity-Vac

Bleeding Brakes with a Mity-Vac
by Michael Hart

A Mity-Vac tool can save you time and effort when bleeding your brakes.

They are available at most auto parts stores, WalMart, and many online outlets.

It is beyond the scope of this write-up, but if you haven’t already done it, clean your brake system first. See the cleaning tip at Master Cylinder "Spooge Holes" and get the spooge out of your calipers too.

If you are already familiar with bleeding brakes the conventional way, here is the quick version of the quirks of using the Mity-Vac:

The tubing that comes with the Mity-Vac will allow some air in around the bleed screw, so you need to use a tie-wrap, or insulated wire, to snug the tubing. Air leakage around the threads of the bleed screw is common also, I've got the best results by wrapping the bleed screw threads with a couple layers of teflon pipe tape to seal them; I can't stress how much this can help. Take care not to pull air in through the master cylinder – the Mity-Vac can draw a lot of fluid through pretty quickly, so keep refilling the master cylinder. Open the bleed screw, secure the tubing on it, and pump the Mity-Vac until no air bubbles are evident, refilling the master cylinder as needed, close the bleed screw, and onto the next caliper.

Sometimes I find the need to finish the job off by hand in the conventional way. See Brake Bleeding Tip for good advice on that.

The splitter (horizontally mounted joint under the triple-tree) can trap air, even using the Mity-Vac. You can tap on it with a rubber mallet or screwdriver handle and may see some bubbles come up into the master cylinder reservoir.

Step-by-step version:
If your brakes feel spongy, if you find the lever creeping closer to the bar after you give it a good squeeze, you need to bleed your brakes. If you haven’t done it for over a year, you need to flush all the old fluid out. See Why Does Brake Fluid Need to Be Replaced Periodically?

DOT3 and DOT4 are compatible, if you don’t know what’s in there already. It’s highly unlikely a previous owner put in silicone DOT5. DOT4 is getting harder to find, being replaced by a synthetic (NOT silicone) that is also compatible.

Put your XS / XJ on the center stand.

Brake fluid is nasty stuff that will eat your paint and plastic, so take preventive measures in case you spill a little around the master cylinder. Wrap and secure a damp rag around the base of the front master cylinder, put a damp towel on your gas tank.

Do the front brakes first. XJ owners, the master cylinder on the handlebar goes to only the right front caliper. The XS front master cylinder goes to both front calipers.

Remove the master cylinder cover, put it someplace it won’t get dirty or wet.

The tool of choice for turning the bleed screw on the caliper is a six-point 8mm closed-end (box) wrench. If you use anything else, take care not to round off the bleed screw.

Loosen the bleed screw about to of a turn, and put the tubing from the Mity-Vac on the bleed screw, securing it by twisting a small piece of insulated wire around it. This is to keep air bubbles from entering the tubing from outside the bleed screw and misleading you into thinking you are still getting air bubbles from the brake system.

Pump up the Mity-Vac, it will start drawing fluid through the system. Check frequently to make sure the fluid in the master cylinder reservoir doesn’t fall below half-full – you don’t want to pull more air in. After a few fillings of the master cylinder reservoir, you should be getting no more air bubbles appearing in the tubing. You want to keeping pumping fluid through until all the old fluid is out of the system and you’re drawing clean fluid with no air bubbles. If you’ve filled the Mity-Vac’s reservoir more than once and are still getting air, it might be that you didn’t really get the tubing secured around the bleed screw.

While the Mity-Vac is drawing fluid with no bubbles, close the bleed screw. (The torque spec is 4.3 ft-lbs – don’t crank this down like superman, okay?)

Remove the Mity-Vac tubing, empty the fluid from its reservoir.

If you have an XJ, you’re done with the front master cylinder at this time, you can replace the master cylinder cover and whatever you used to protect against spillage.

XSives move on to the other front caliper. The single line from the master cylinder goes to a splitter under the triple-tree. After bleeding the second caliper tap on the splitter with a screwdriver handle or something and look for air bubbles appearing the in master cylinder reservoir. In stubborn cases, you might have to let things sit overnight (secure the master cylinder cover to prevent moisture in your fresh brake fluid!) and do some more tapping (or even bleeding) in the morning.

If the lever feels anything but solid and firm when you give it a squeeze, you may need to finish the job using the conventional method outlined at Brake Bleeding Tip

Follow the same steps for the rear brake. It can be more troublesome as its master cylinder is not elevated like the front one. Spillage is not as problematic, but the location can be a bit awkward, take your time.

XJ owners: Your rear master cylinder actuates the rear caliper and the front left caliper, through the splitter under the triple-tree. Bleed the front left caliper first, then the rear. You may need to do the front a second time after the rear.

Do this once a year, flushing out all the old fluid, and you’ll probably never have to clean out spooge again.

Bonus tip:

Speed bleeders make brake bleeding an easy and quick one man job. They have a one way valve and sealed threads that prevent air from being sucked into the system during the brake/clutch pedal up stroke. If you are installing Speed Bleeders (highly recommended) just completely unscrew the original bleeder nipple and screw in the speed bleeder. You will feel resistance when the thread sealer starts to screw into the caliper. Torque the speed bleeder to only 32-40 inch pounds (about 3 foot pounds). That's like having a one foot long wrench with a 3 pound weight on it (not much torque). Go easy on them. You don't need to know the size of your bleeder nipples when you order speed bleeders, just tell them the year and model of your car/motorcycle, they know what fits.


For more info check out the Speed Bleeder Website

Last edited by crazy steve; 04-03-2012 at 12:51 PM.

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