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Old 12-27-2016, 09:34 PM   #19
CoryM
 
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Originally Posted by dogsridewith View Post
Last two posts sound great. There are several ways to move brake fluid through the system. I do it w/o assistant using a MityVac (suction device, w/ gauge, also used for testing various vacuum diaphragms). Ever encounter or hear trusted account of the Mity Vac pulling in air around wheel cylinder or master cylinder seals...thereby, of course, ruining the bleed job.
I've never seen air pulled into the system except for when master cylinders fail (or when someone lets the fluid level get too low). The suction will cause air to pull past the nipple threads and into the system but it immediately goes out the nipple. This is why you will see bubbles in the mityvac even though its well sealed to the nipple. The amount of air that remains is not enough to cause issues for street cars or even be noticeable when testing. On a high end racecar you may want to give it a few manual bleeds, but I've not found that required on the ones I've played with. Professional brake flush machines are just vacuum suckers on each bleeder, and several PSI of fluid on the master cylinder. It's probably a bit better than just vacuum, but mostly it's probably just faster. We also put 2L of fluid through the system which is probably excessive for most cars, but some sure need it.

One day I should do a write-up or video about brake servicing. Very few people do it properly.
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Old 12-27-2016, 09:46 PM   #20
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Interesting I would really like to see a good write-up or video on brake bleeding I think that's a great idea. You're right being as that it really hasn't changed a lot and over a hundred years there are a lot of people who still must understand it and the whole notion is sometimes a little mysterious as to when and how. It seems the same is true of disc brake servicing. I have seen a lot of brake jobs done and I've seen as many different ways of doing it as I have seen technicians to do it. Some technicians Grease the pad Hardware. Some people put silicone lubricant grease oil whatever on the back of the pad and swear by it. A lot of people misunderstand what a pad shim is what it does. Getting straight answers to these questions has been sometimes difficult. Even out of the manufactures themselves. I of course have some strong opinions on it being in the automotive service business an automotive parts business my whole life. But as strong as my opinion on what to do I still get a lot of people who disagree. Take the pad hardware for example I get people who swear by lubricating the pad Hardware. I strongly believe that grease and oil attract dust and debris. I don't lubricate them. Not to mention all the ones I sell these days come with a pre lubricated Teflon coating to them. But there are many varied opinions on how to do this and what works.

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Old 12-28-2016, 12:27 AM   #21
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Quote:
Originally Posted by dogsridewith View Post
Last two posts sound great. There are several ways to move brake fluid through the system. I do it w/o assistant using a MityVac (suction device, w/ gauge, also used for testing various vacuum diaphragms). Ever encounter or hear trusted account of the Mity Vac pulling in air around wheel cylinder or master cylinder seals...thereby, of course, ruining the bleed job.

I have tried the mighty vac and no matter what it pulls air in through the bleeder for me. That is even with covering it with grease as well as using thread sealant tape.

I just use the 2 person method which is cheap. Quick and woke well.

Down the road I'll likely buy a pressure bleeder but for now the 2 person works fine
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Old 12-28-2016, 09:35 AM   #22
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I'm not buying the fact that the mighty vac is pulling air with grease and thread tape. That does not make coming sence. Think about that. You think because you see air in the line it came from ambient air? Not likely. What is more likely is the mighty vac is in a vacuum. All matter and it's state are affected by atmospheric pressure or lack thereof. In other words you don't find a lot of water 4 brake fluid for that matter in its liquid form in a vacuum. The reason being without the atmospheric pressure of the Earth's atmosphere water becomes a gas. When you use the Mighty vac it pulls a vacuum a strong vacuum with the bleeder being the orfice tube in the system. Anything behind that or forced tube is in a strong vacuum. What you're seeing is air. But likely where it came from his lack of atmosphere causing vapor to boil. This is called Boyle's Law

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Old 12-28-2016, 09:58 AM   #23
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I have tried the mighty vac and no matter what it pulls air in through the bleeder for me. That is even with covering it with grease as well as using thread sealant tape.

I just use the 2 person method which is cheap. Quick and woke well.

Down the road I'll likely buy a pressure bleeder but for now the 2 person works fine
I agree mityvac is overkill. Spend your money on something useful!
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Old 12-28-2016, 03:48 PM   #24
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Mityvac nipple bubbles

Mityvac instructions say you will see big spurty bubbles when air is coming out of the system, then steady little bubbles (which are no problem) of air being pulled through the loosend nipple's threading (from ambient air) and mixing with fluid being pulled through the system...into the cup...until the nipple is closed...all the while with the operator paying attention to the gauge and squeezing the vacuum pump handle enough to maintain some vacuum.
There's no vacuum diaphragms to Mityvac check on Yaris? People would have saved millions of dollars tuning the late 1980's Tercel fleet finding broken diaphrams in distributor advances and emissions gizmos instead of buying new or rebuilt carburetors.
---
I can see using some grease on bleeder nipples to prevent rusting, but grease or Teflon tape can't be expected to seal straight threads. The seal is at the end of the nipple.

Last edited by dogsridewith; 12-28-2016 at 04:30 PM.
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Old 12-28-2016, 04:26 PM   #25
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Air will pull past the coarse bleeder threads when using vacuum on the bleeder. Especially on rebuilt calipers with poorly machined threads. The threads are not designed to seal at all, and are loose enough that even fluid can pass through them readily when the bleeder is loose (which is annoying because it means when I do flushes, brake fluid drips on the hoist). Just make sure to close the bleeder while there is a vacuum still on it and you shouldn't have any air problems. If you loose vacuum while the bleeder is open, it will pull air back into the brake system. The mityvac may be harder to use than a flusher because of this. The best way to use the mityvac for the final bleed is probably to pump the hell out of it with the bleeder closed, crack the bleeder and then close it again before vacuum runs out. Otherwise you may keep getting air sucked back into the system.

Do not use any petroleum based greased where it can contact your brake fluid or rubber. It will swell the seals and destroy them.
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Old 12-28-2016, 05:00 PM   #26
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The problem I had was that not enough fluid was being drawn down to the bleed nipple to do an adequate flush and bleed. The vacuum was being maintained without issue but I find putting pressure at the main reservoir always flushed way more fluid through the system. I would have a small drop with the mighty vac and a full rush of fluid with the 2 person method.

As long as you have a helper and a block of wood to stop the pedal from going all of the way down it take very little time and gets everything through the brake lines and out.
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Old 12-28-2016, 05:59 PM   #27
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Why you should not hit brake pedal to the floor ??
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Old 12-28-2016, 07:05 PM   #28
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Why you should not hit brake pedal to the floor ??
Because the master cylinder piston only moves around 1/2 stroke in normal use. The bore wears, which leave a ridge at the end of it's normal stroke. So when you bleed and go all the way to the floor, the rubber piston seal has to go over that ridge and it tears. Then you have to replace the master cylinder.

Never go more than 1/2way to the floor when bleeding (unless master cylinder has just been replaced).
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Old 12-29-2016, 12:48 AM   #29
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So like said ... pedal to the metal !!
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Old 12-29-2016, 02:12 AM   #30
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Originally Posted by tmontague View Post
The problem I had was that not enough fluid was being drawn down to the bleed nipple to do an adequate flush and bleed. The vacuum was being maintained without issue but I find putting pressure at the main reservoir always flushed way more fluid through the system. I would have a small drop with the mighty vac and a full rush of fluid with the 2 person method...
Then your problem was unclogging the system BEFORE being able to bleed it.
I've only seen this level of clog--rusty dirt-- happen inside the tip of the nipple, or maybe just inside the wheel cylinder...resolved by removing the nipple completely and clearing nipple/cylinder with a drill bit(s). Stomping the pedal would certainly produce more system pressure to clear rust in the lines, sticky proportioning valves, etc.
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Old 12-29-2016, 09:59 AM   #31
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Originally Posted by CoryM View Post
Air will pull past the coarse bleeder threads when using vacuum on the bleeder. Especially on rebuilt calipers with poorly machined threads. The threads are not designed to seal at all, and are loose enough that even fluid can pass through them readily when the bleeder is loose (which is annoying because it means when I do flushes, brake fluid drips on the hoist). Just make sure to close the bleeder while there is a vacuum still on it and you shouldn't have any air problems. If you loose vacuum while the bleeder is open, it will pull air back into the brake system. The mityvac may be harder to use than a flusher because of this. The best way to use the mityvac for the final bleed is probably to pump the hell out of it with the bleeder closed, crack the bleeder and then close it again before vacuum runs out. Otherwise you may keep getting air sucked back into the system.

Do not use any petroleum based greased where it can contact your brake fluid or rubber. It will swell the seals and destroy them.

Sounds like an excellent reason not to use a mityvac.
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Old 12-29-2016, 11:22 AM   #32
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Which reason are you addressing? Air pushing past bleeder threads is irrelevant. I never come close to loosing vacuum with the bleeder open. The gauge is right there to watch and I'm just cracking the bleeder w/ an 8 mm wrench while watching the fluid/bubble mix run through clear tubing...very easy to stop in an instant w/ a tiny movement of the wrench. MityVac has enough vacuum reservoir to do this easily. It helps if everything is attached (the tubing to the bleeder nipple, and all other tubing pieces) and hung/placed (the pulled-fluid receiving cup) sufficiently.

Last edited by dogsridewith; 12-29-2016 at 12:47 PM.
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Old 12-29-2016, 12:45 PM   #33
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Which reason are you addressing? Air pushing past bleeder threads is irrelevant. I never come close to loosing vacuum with the bleeder open. The gauge is right there to watch and I'm just cracking the bleeder w/ an 8 mm wrench while watching the fluid/bubble mix run through clear tubing...very easy to stop in an instant w/ a tiny movement of the wrench. MityVac has enough vacuum reservoir to do this easily. Lots of auto mechanic work takes two or three hands. This, just one, if everything is attached (the tubing to the bleeder nipple, and all other tubing pieces) and hung/placed (the pulled-fluid receiving cup) sufficiently.
CoryM says one thing and you say the opposite. You guys settle it.

As for me I can bleed my brakes all by myself without a mityvac and usually without help. Ive bled the brake system of the ST1300 motorcycle alone, a VERY Rube Goldberg system with TWO master cylinders one lever actuated one front brake rotor actuated! Very complicated and very nuts!

How nuts? The front wheel has two discs each with its own caliper. When its pads grab the disc, the left caliper pivots actuating a secondary master cylinder, which applied the rear brake. Actually, it applies one piston of the three pistons on the rear caliper. Totally CRAZY! VERY complicated!

I can always get someone to help if needed.
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