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Old 09-05-2004, 09:26 AM   #1
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Default Brake Bleeding

I see,

NOw I decide to replace the master cylinder, but I am little worried about the bleeding.

I ve seen one time when mechanics do the job before.
One guyes sitting in the drivers seat, yelling...something. Push..then the other guy did something to the wheel. I rarely understood the bleeding procedure after reading the manual.

But...still skeptical.
Do I have to buy the "Mityvac® Brake Bleeder Kit " or something?.
Any tip for bleeding would be appreciated.

Thanks.
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Old 09-05-2004, 07:36 PM   #2
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OK, The idea is to remove any air bubbles in the brake lines from the master cylinder to each wheel cylinder (rear wheels) or caliper (front wheels).

These directions presume you have a good master cylinder or a new one that has been bench-bled.

You will probably need to remove the rear wheels to gain access to the wheel cylinder bleeders. You may be able to get at the front bleeders on the calipers by turning the wheels all the way left or right. I find bleeding is a lot easier with all the road wheels removed and the car up on stands. Never get under a car supported only by a jack!

Start by filling the master cylinder reservoir and replacing the cap. Don't let brake fluid be exposed to the air - it will absorb moisture from the atmosphere which can cause troubles in the brake lines. What you want is to have a helper pump the pedal a couple of times (press down - release; press down - release) then press down and hold. While he is maintaining pressure on the pedal, you open the bleeder valve on the wheel cylinder or caliper and relieve the pressure by releasing fluid from the bleeder valve. The brake pedal will suddenly go down, at first nearly all the way to the floor. The helper must not allow the pedal to come up while the bleeder valve is open or air will be sucked in through the bleeder valve. At the wheel, when the fluid flow stops, close the bleeder screw and instruct your helper to release the pedal, then "pump and hold" again. After a few times, depending on how much air is in the lines and where the air is located, you will notice as you open the bleeder valve, that the fluid flow is interuppted by escaping air. It kind of makes a "spitting" sound. That is good - that'* the air you are trying to remove. Keep repeating the procedure until the stream of fluid is solid - no air - and clean in appearance.

While you are bleeding each wheel, after about five or six squirts, check the level of fluid in the master cylinder reservoir. If you let the reservoir go empty, you will introduce air into the lines and you will have to bleed the master cylinder and all the brakes again.

I like to place a box wrench on the bleeder screw nut in a position that allows me to both open and close the valve (hopefully) without repositioning the wrench. I then attach a length of flexible vinyl tubing (maybe 3/16" inside diameter) that fits tightly over the end of the nipple on the end of the bleeder. I run the hose into a plastic pan to catch the fluid that comes out. Be careful, brake fluid removes paint. Also, don't use more than a couple of foot-pounds of torque to close these little bleeder screws - they are not solid and they can break off very easily.

There are a couple of inexpensive one-man methods. You can use a vacuum pump to suck out the air from each line, but the problem with that is that you have to open the bleeder screw to open the line and when you do, you usually end up sucking some air through the threads on the bleeder screw making it difficult to know when you have all the air out. An older method is to take the hose described above and put it into a (clean and dry) coke bottle with the end of the hose submerged under a couple of inches of brake fluid. This is not a bad idea, even with a helper, cause if your helper screws up and releases the pedal when the valve is still open, it will suck mostly fluid in from the bottle instead of air. The problem with this method is the same as with the vacuum pump. That is, on the release stroke, if the valve is open, air can be sucked into the system through the threads on the bleeder screw.

Be careful if your bleeder screws are corroded. They will break off in the cylinder or the caliper with surprisingly little force applied, and then you have a real piece of work on your hands. A good plan is to squirt around the bleeder screw (not into it) with a good penetrating oil like power blaster, kroil, or sea foam deep creep (WD-40 is not very good for this). Remove the cap from the screw and give it a couple of taps square on the end of the screw with a small ball-pein hammer, and squirt again to encourage the oil to penetrate the threads. Best if you can let it sit overnight, but give the oil at least 30 minutes to work before you try to open the bleeders.

If your bleeders don't have the little rubber caps on them, make sure the passage is clear to let the fluid out. Sometimes you have to clean them out with a small drill bit.

The traditional method is to start at the wheel farthest from the master cylinder, usually the right rear, and work to the shortest run, i.e., the left front. As you work your way around, the pedal should become firmer and progressively higher from the floor. When you are done, if you have removed all the air, the pedal should be firm, there should be no "sponginess," or softness when depressed.

Good luck!
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Old 09-05-2004, 07:42 PM   #3
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Damned good write up. Techinfo?
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Old 09-05-2004, 07:57 PM   #4
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I'd be pleased to see it in techinfo. This site has been so helpful to me, I'm glad to get the chance to help others.
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Old 09-05-2004, 08:03 PM   #5
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wow, that was very in-depth! I dubb this "techinfo worthy"!


-justin
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Old 09-05-2004, 11:34 PM   #6
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i would be careful using wd-40 around anything rubber. im not sure about wd-40, but most lubricants make rubber expand, which means getting new parts. i would be careful about using lubricants around brakes.
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Old 09-05-2004, 11:49 PM   #7
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I have speed-bleeders installed on all four of my brakes. There is a check valve there that only allows brake fluid to flow out, and does not allow any air in. This allows you to bleed the brakes yourself.
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Old 09-06-2004, 12:20 AM   #8
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If you'll be replacing the master cylinder, then you'll need to 'bench bleed' it before even installing on the car and then bleeding each corner.

If you don't bench bleed the master cylinder, you will never get all the air out of it. You should recieve an instruction sheet with your master cylinder on how to bleed it, follow the instructions precisely.

Cheers,
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Old 09-06-2004, 04:01 AM   #9
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Default Great

Great description.

Now I can imagine how to do that.

Can I ask one more question?.

Beofre this, how to deplete the brake fluid from the reservoir?...
Straw?...

Thanks. again.
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Old 09-06-2004, 09:26 AM   #10
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Well you can bleed for a while till it all comes out the system [if you have time, I say go this route], then keep adding fluid as you go along. If you don't have that kind of time, go for a syphon [sp?].. one with a hand pump will work fine [brake fluid in your mouth can't be good]. But before you start the bleeding process, add in some new fluid .


-justin
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