Brake Bleeding... theres got to be a better way.

[SAmadei]

So... I've been working on a lot of brake lines... basically, I have two cars which have required nearly complete brake line replacements.  Unfortunately, in order to adapt and fit new lines in a car without taking it completely apart, you use unions... and in retrospect, I seem to have gotten some unions that do not seal well... so I've had several cycles of bleed brakes - observe leak - take apart everything and tighten fitting - rinse and repeat.

In any case, I hate doing any work to the car that I cannot do solo... and the one man bleeding solutions out there just suck.

This got me to thinking... How do manufacturers "install" brake fluid?  Its obvious that GM is not bench bleeding master cylinders and then two-manning a full system bleeding.  After some research, it appears that manufacturers do something akin to how they "install" refridgerant... they pull a vacuum then switch over to a source of brake fluid... letting the brake fluid suck into the system without any air being introduced.

So I got to thinking about this and I figure this would not be difficult to implement at home... except for the fact that your system already has some old brake fluid in it.

In AC systems, when you pull a vacuum, all the refridgerant, oils, water, etc. boil off and is pumped out by the vacuum pump. 

My question is what would happen if you did this to a brake system?  Would the brake fluid boil off?  If the brake fluid did not boil off, would the air beyond the brake fluid get pumped out?  If the brake fluid boils off, would it condense once outside the vacuum pump?

Thoughts?

[G. David Felt]

Yea old days of add brake fluid and craw under and bleed and then add more brake fluid and move to the next wheel are really out of date now.

 

Some pretty good brake bleeding products are out there now for DIY.

 

http://www.brakebleeder.com/product-category/brake-bleeders/

 

http://www.summitracing.com/search/department/tools-shop-equipment/part-type/brake-bleeder-kits/?autoview=SKU

 

Both these companies have a good assortment of systems for this.

[SAmadei]

Yea old days of add brake fluid and craw under and bleed and then add more brake fluid and move to the next wheel are really out of date now.

 

Some pretty good brake bleeding products are out there now for DIY.

 

http://www.brakebleeder.com/product-category/brake-bleeders/

 

http://www.summitracing.com/search/department/tools-shop-equipment/part-type/brake-bleeder-kits/?autoview=SKU

 

Both these companies have a good assortment of systems for this.

I've used several of these and they never work perfectly right for me... usually leaking or the plastic parts wear out quickly.  Granted, I have not used the top end kits.  Also, reverse bleeding is reported to potentially damage seals and it seems to me that it would trap air in the master cylinder... which is why it needs bench bleeding in the first place. 

This is not what I had in mind... what I have in mind would not require touching anything but the master cylinder.

[balthazar]

Tho I've done brake line replacements twice, I have no advice here. Didn't have any major issues; did one by myself (bench bleed/ line in mayonnaise jar) and the other I had a helper. The "other" is my '04, so it has ABS and a long chassis; a bunch of unions.

I'm about to bleed my '40, maybe something will occur to me during that process.

[Drew Dowdell]

I was about to do my own brakes on the CR-V, but it needs calipers too and I didn't want to have to deal with bleeding them.... so I just dropped it at Monroe.  I don't have the time to be messing with it.

[SAmadei]

Maybe I need to be a bit more clear.

Unless someone knows better, manufacturers "install" brake fluid by using a vacuum pump on the master cylinder... pull a vacuum, switch to brake fluid... vacuum pulls brake fluid into system, air-free.  No other part of the system is touched.

I could easily build such a tool, however, my brake system has brake fluid and, most likely, air behind some of that brake fluid.  In a vacuum, most liquids will boil off and get sucked out... but I don't know if DOT3 will.  If it does not, would a vacuum pull the air which is behind the brake fluid?  Does anyone know what would happen to brake fluid in a vacuum?

What I really need is some glassware that can withstand a vacuum... so I can see what happens.

What I like, though, is if the DOT3 _does_ boil off, it would be possible to use such a tool to flush the system by removing old fluid.

 

Edited July 19, 2015 by SAmadei

[Drew Dowdell]

How much vacuum are you planning to pull.... and why are you using DOT3?  DOT4 is supposed to be much better. 

 

Minimum DOT4 boiling point is 446F (without a vacuum)

Minimum DOT3 boiling point is 401F (without a vacuum)

Amsoil DOT4 claims to be good to 580F

 

I can't imagine you would be able to pull enough cause it to boil off.  You just need to pull all the old fluid out first and then let the new stuff flow behind to clear out bubbles.

[SAmadei]

How much vacuum are you planning to pull.... and why are you using DOT3?  DOT4 is supposed to be much better. 

 

Minimum DOT4 boiling point is 446F (without a vacuum)

Minimum DOT3 boiling point is 401F (without a vacuum)

Amsoil DOT4 claims to be good to 580F

 

I can't imagine you would be able to pull enough cause it to boil off.  You just need to pull all the old fluid out first and then let the new stuff flow behind to clear out bubbles.

I drive with the gas, not the brake... I've never had a problem with brake temperatures and DOT3 is what the car had... and its cheaper.

Dexcool was supposedly better, too... but its been removed from most of my cars because it seems to be better at rotting the cooling system.

 

Anyway, I'd be pulling the same amount as if I was evacuating the AC system... they go surprisingly low.  Brake system has a smaller volume as the AC.

While you never get a perfect vacuum, even at near vacuum, a lot of liquids' boiling points drop real fast.  I wish I could find a phase diagram for brake fluid or polyethylene glycol... but most searches give me ethylene glycol.