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brake bleeding. Best method????
https://slantsix.org/forum/viewtopic.php?t=44807		 Page 2 of 2
Author:  olafla [ Mon May 09, 2011 10:31 am ]
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Here's the text on brake bleeding from the '78 manual.

ImageImage

Beware, there may be differences between the brake system on older cars and the one showed here.

When bleeding the system alone, the vacuum method I described earlier is fast enough, and will behave the same as 'gravity bleed' described in the text.
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So to people who are particularly sensitive to their car (or me as a mechanic who feels and notices every slight quiet creak and bump that alot of my customers dont even notice) a vacuum bleeder does provide somewhat softer of a pedal.
:?: :?: :?: :?: :?:

No way! Sorry, but if your pedal is softer after a brakebleed with vacuum bleeding than it is with pressure bleeding, it is not from the method used, but more likely from the person doing the job! The very point of bleeding a brake system is that air is compressible, brake fluid is not. Soft or spongy pedal when the car is not moving, means air in the system. The same feeling only when the brakes are hot, may indicate minute amount of water in the system, that may evaporate and create compressible steam bubbles when heated. The expansion into steam is very violent, so if you have any suspicion of water in the system, bleed it at once!

I have personally had both good and negative experiences with speed-bleeders. For those not familiar with them, they are just a piece of hose with a one-way valve at the end that goes down into the jar. I have had two sets that actually leaked, and one of them that was submerged in the jar, just moved the brake liquid back and forth when pumping/releasing the pedal. Being on the last wheel cylinder, there was already enough brake fluid in the jar to fool me.

64 convert: Sounds like a bad master cylinder bleed, and they may also have pressure bled the rest of your system at a too high pressure, see the text for a possible incorrect procedure used.

Use a manual! if you don't have one, RockAuto has both CD and printed manuals.

Olaf.
Author:  thechristopherh [ Thu May 12, 2011 5:16 am ]
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Sorry, but if your pedal is softer after a brakebleed with vacuum bleeding than it is with pressure bleeding, it is not from the method used, but more likely from the person doing the job!
I am an ASE certified Master Technician at Lexus with a California Smog License. (And this is common knowledge amongst technicians at my Lexus dealership) You are one of the 10% of customers who can't tell the difference. Trust me it is really insignificant but it's there, I test drive 3-10 cars a day, 4 days a week (we work 4 ten hour shifts) to see if we can certify them as pre-owned, this includes feeling the brake pedal and bleeding as necessary. That makes that between 12-40 cars a week. I know what I am talking about.

Sucking air out will take much much longer to get 100%, rather then 98% of air out(if it even does) then pushing it out. And most people can't tell the difference. But at any rate pneumatic vacuum bleeder is plugged into a compressor and has a switch on it. I'm not sure how you can possibly have operator error there, especially when I have done at least a hundred brake flushes since the beginning of the year.

And a quick google search reveals the exact reason why: http://www.veryuseful.com/mustang/tech/ ... eding.html
"Bleeding by vacuum and speedbleeders *depends on* your ability to get a *perfect* seal between the threads of the bleeder screw and the caliper (or brake cylinder). You do that with special grease or coatings."

think about it, if your bleeder screw threads aren't air-tight then a VERY SMALL AMOUNT OF AIR can get in that way, and the only way you can be sure they are completely air sealed between the threads and the caliper is to either close them (in which case you can't bleed it) or have grease on all your bleeder screws...
Author:  olafla [ Thu May 12, 2011 11:07 am ]
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Interesting reading, thechristopherh, I have never heard of such differences between vacuum- and pressure operated professional systems before. Still, the problem is locked-in air in the system after the bleed, and that is bad. The only spongy pedal feeling I ever had, and even after repeated bleeding, was with the earliest silicone-based brake fluids, for unknown reasons. I have bled brakes for 40 years, but not on a professional level like you.

I don't know if you will agree, but I find some of the methods in the link you provided, rather questionable. The often moist and dirty air from inside a tire, is not something I would like to have in contact with my brake fluid. It is hardly a big problem, but even in the small hand operated pressure cans, there can be a surprising amount of water in the compressed air, The air provided for pressure bleeding, should be clean and dry.

I still think the small scale vacuum method I have always used, is a great method for bleeding brakes alone. I feel that this method also provides the least likely way to get air into the system again, as it is suction all the time. After all, we are talking about hobby mechanics working in a garage or driveway, without the resources of a professional workshop. Personally I have never been rushed when doing such a job, and I have always taken great care to do it right. Besides, time spent working with my car is always quality time! 8)
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You are one of the 10% of customers who can't tell the difference.
I am not quite sure what you mean by that.

Olaf.

BTW, I have the old style oval lid on my master brake reservoir, not a screw lid, so I would guess it is not easy to fit a pressure bleeder on it anyway.
Author:  Charrlie_S [ Fri May 13, 2011 3:06 am ]
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Quote:
"Bleeding by vacuum and speedbleeders *depends on* your ability to get a *perfect* seal between the threads of the bleeder screw and the caliper (or brake cylinder). You do that with special grease or coatings."

think about it, if your bleeder screw threads aren't air-tight then a VERY SMALL AMOUNT OF AIR can get in that way, and the only way you can be sure they are completely air sealed between the threads and the caliper is to either close them (in which case you can't bleed it) or have grease on all your bleeder screws...
And that is why I don't like speed bleaders. I tried them once, and had that exact problem, and I could feel the air in the system. What type of grease/sealer would you use on the threads?
Author:  wjajr [ Fri May 13, 2011 5:22 am ]
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Charles you took the words out of my mouth. What dose one use to seal bleeder threads?

Recently I purchased a pair of KH rebuilt calipers by Raybestos. I have run close to 3 pints of brake fluid through them trying to get a firmer peddle using the one man hose & jar method which in the past has yielded good results.

After examining both calipers I concluded the bleeder screws are too loose when backed out, and allow air to reenter when peddle is released when pumping.

My solution would be to get a second set of feet to pump brake peddle while I opened & closed bleeder after each pump. But, I don’t have a brake buddy handy. Grease I can get…

Bill
Author:  emsvitil [ Fri May 13, 2011 1:37 pm ]
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I wrap teflon tape around the bleeder screws to seal them from outside air.


And I use DIY speed bleeders......


Aquarium airline check valve (rubber diaphram type)
Author:  wjajr [ Fri May 13, 2011 2:47 pm ]
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Ed:
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I wrap teflon tape around the bleeder screws to seal them from outside air.
Teflon is good to 6 or 700 degrees F so it probably is ok to use on a bleeder screw.

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Aquarium airline check valve (rubber diaphram type)
I’m not clear on this airline check valve application. Probably because I’m not familiar with Speed Bleeders.

Do you fit the valve between bleeder and jar of expelled fluid to keep backwash of air & old fluid?

I just looked up brake speed bleeders. Interesting device, I’ll consider using them on the Dart.
Author:  emsvitil [ Fri May 13, 2011 4:36 pm ]
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Quote:
I’m not clear on this airline check valve application. Probably because I’m not familiar with Speed Bleeders.

Do you fit the valve between bleeder and jar of expelled fluid to keep backwash of air & old fluid?

I just looked up brake speed bleeders. Interesting device, I’ll consider using them on the Dart.

Bleeder screw, short section of tubing, check valve, rest of tubing.


Fluid (and any air) can only flow out past the check valve. So you don't need to reseat the bleeder screw with every pump of the brake pedal.
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