Front brakes won't bleed, even with vac! - Page 2 - PeachParts Mercedes-Benz Forum

83TD · #16 03-20-2011, 10:39 AM

I have tried using a Vacula vacuum bleeder on my 83TD with poor success. I think the horizontal bleed screws on the MB calipers allow air to flow back into the caliper past the threads. So I now use a pressure bleeder that seems foolproof.
The Vacula works fine on my BMW motorcycles which have vertical bleed screws. YMMV
Peter

JHZR2 · #17 03-20-2011, 10:57 AM

Especially on these older cars, lines can be in very bad shape...

Yak · #18 03-20-2011, 12:21 PM

Quote:

Originally Posted by imagesinthewind

So, you may remember that I needed a new master cylinder back in Sept or so.

I had some trouble getting the front brakes to bleed. Took everything off and tried again. The back bled easy. The front still nothing. I bought and tried a mightyvac and while I can draw some brake fluid out of the left front, when the brake is pressed, no fluid comes out on it;s own. The right front has brake fluid coming out, but not shooting out like the back does.

I had a vac leak, but I used black gasket stuff and that is solved.
So, What the H3LL am I to do now? Even the mighty vac doesn't seem to help. And my hand hurts from trying. Is ther a way to get the vac to blow instead?

I can feel the air sucking and blowing on my finger if I hold it over the screw.
YES there is a full front chamber on the res, I pumped it up with the little pump on the top of the res. If I can feel the air sucking and blowing, see a small bit of fluid blow out of the screw, then there is not a blockage.
I am loath to take it all off again, I'd lose the gasket I made.

What can I do, please help! Thanks to all!

Ginny
78 300SD

Going back to the original post: "Can you get the vac to blow instead?" No. Vacuums are low pressure so they by nature "suck" and nature abhores them.

However, depending on the Mity-Vac, you can get the pump to blow simply by changing the orientation of the hoses. If you have an intake hose (the vacuum end on the "front") and an exhaust hose (the pressure end on the "top") you simply swap the lines.

But if you can't get the vacuum to draw fluid from the bleed nipples after hand pumping to the level of pain then something is wrong. Maybe the nipples are gunged up - does the gauge read high levels of vacuum? Maybe they're too loose - does the gauge needle swing a bit but return to zero?

I'd go methodically:

1) Inspect every fitting and line from your MC, through the hard lines, to the hoses, to the calipers, to the nipples.
2) You do have the rubber caps on the nipples, right? If not, and you're in the rust belt then order new nipples for the calipers and replace them. Brake fluid is hygroscopic and it's attracted water into the nipples and rusted and gunged them up.
3) Since your lines are 6 years old AND you've had trouble AND you're bleeding the system anyway, replace them. BE VERY CAREFUL WITH THE HARDLINE/HOSE FITTING. USE THE CORRECT WRENCHES AND LET SOAK WITH PENETRATING OIL OR YOU'LL STRIP THE FITTING OR CRIMP THE HARDLINE.
4) Top off the reservoir with clean fresh fluid from a new bottle.
5) You can use the vacuum to draw the fluid out of the nipple, but expect lots of air early on. DO NOT LET THE RESERVOIR GET LOW.
6) When you're drawing mostly clean fluid and some air, it's time to change to pressure bleeding.
7) You can use a one-man pump; or a two-man pedal technique. DO NOT HAVE THE ASSISTANT USE FULL PEDAL-TO-THE-FLOOR STROKES OR YOU CAN DAMAGE THE PISTON. Short "burps" to get the remaining bubbles out.

Can you post a pic or be more descriptive of the gasket out of the "black gasket stuff"? Homemade gaskets on brakes sounds like a bad idea.

http://www.quotecounterquote.com/2010/02/nature-abhors-vacuum-famous-writers.html

imagesinthewind · #19 03-20-2011, 01:19 PM

The gasket is between the master cyl and the brake booster. It won't effect the way the brakes work, just the vacuum that allows the car to shut off with the key and not keep running.

Getting new tires all around for her today too if I get the brakes done.

leathermang · #20 03-20-2011, 01:21 PM

Quote:

Originally Posted by Yak

....7) You can use a one-man pump; or a two-man pedal technique. DO NOT HAVE THE ASSISTANT USE FULL PEDAL-TO-THE-FLOOR STROKES OR YOU CAN DAMAGE THE PISTON. Short "burps" to get the remaining bubbles out.

Lets be very clear on this part...

for pumping up by the person in the car.. typically a few light pumps will do.. that person HOLDS the pressure on the pedal.. and calls to the person underneath " holding"...

BUT THE RESPONSIBILITY OF NOT LETTING THE PEDAL GO FURTHER THAN IT SHOULD IS THAT OF THE PERSON AT THE BRAKE BLEEDER VALVE.

a QUICK open close... pretty much as fast as you can close it as you get a stream of brake fluid coming out is the trick.... it is ONE MOVEMENT.. OPEN-CLOSE the bleeder... you do it as often as there is bad looking fluid and or air sputtering, etc.. until you get clean solid flow of new brake fluid.

This means the pedal inside the car can not travel further than usual.. with the potential of messing up a seal from a rusted rod traveling too far...
that is the reason behind all this care... you do not need to make more problems than you started out with by maxing out the rod travel. That will serve no useful purpose.

whunter · #21 03-20-2011, 03:37 PM

How to Bleed Your Brakes
http://www.popularmechanics.com/cars/how-to/maintenance/4213448

http://www.youtube.com/watch?v=c0IdNb3hEqI&feature=related

imagesinthewind · #22 03-20-2011, 05:35 PM

FIXED!!!

Thanks so much vtech for all of your private, helpful messages!! All done and they are great. Nice and hard where needed. Now I need to adjust my parking brake. How do I do that? LOL!

Thanks to all who gave me great advice. Car is all fixed, bathed and ready to drive around tomorrow. LOVE IT!

Ginny

compu_85 · #23 03-20-2011, 07:03 PM

A motive bleeder makes this job a snap. With the wheels off it only takes 10min to bleed the brakes. Dump in fluid, pump up the pressure, connect your line going into your catch can, open the valve, and pump the brake pedal a bit to help things along.

If you spot crappy brake lines on your car my suggestion would be to bleed the system now, and order up new lines. When you replace them you'll have to bleed a bit more fluid though, but that can help push out any remaining junk in the calipers the first bleed missed.

-J

Quirky Mercy · #24 03-20-2011, 08:03 PM

Quote:

Originally Posted by leathermang

It may have worked well for you.
but it is not good advice for bleeding brakes...and we have no way of knowing how well it really worked for you... specifically whether it left some old brake fluid in your system....this is also the reason you bleed the longest line first... so that when the others are bled you know that NEW fluid it being run into them....
You need a secure one way function.. new fluid in at the top, air and old fluid and junk pushed out at the bottom with force. Not ' some ( unknown amount ) out at the bottom and sucking back in'...
There is also the matter of the threads of the bleeder potentially letting air back in on the suck as that flows easier than the new ( and lower situated ) new fluid...
The regular system is easy and fool proof. Don't try to get tricky or lazy on Brake items...
And do not think I do not know how much trouble it is to get help for this procedure done right if you do not have a bleeder....as I do not... and train the helper.... 40 years of being a one man operation on mechanicing...

Well someone should tell my Auto Shop teacher and my Grandfather. both of them had shown me this procedure. And they had more knowledge than both of us. They were not lazy either. If You had ever tried it you would know you will go through about a half quart of fluid so i doubt there is any old fluid in there.

I am glad the poster got his brakes fixed, I was just trying to show another method that works when you have no help.

leathermang · #25 03-20-2011, 08:30 PM

Sorry Quirky Mercy, the physics are just not with you...
that is why others are not recommending the procedure that you described either..... there are basic physics problems with it...as I was careful to point out.

vstech · #26 03-20-2011, 08:46 PM

several ways to bleed brakes in a car.
one. open the bleeders, and let fluid flow out of the bleeders. it can work, but it's not a sure thing for getting air out of the steel lines.
two. pedal bleed, pushing pressure into the system and loosen the bleed screws, then tighten them before pedal is released, and repeat.
three, power bleed with pressure tank, full of fluid, filling the reservoir and releasing it out the bleeders.
four, multi line, reverse bleeding, with pressure pushing fluid and air UP backwards into the reservoir.
all other ways are incapable of properly bleeding brakes properly without extreme luck!

leathermang · #27 03-20-2011, 09:00 PM

Quote:

Originally Posted by vstech

...several ways to bleed brakes in a car.
one. open the bleeders, and let fluid flow out of the bleeders. it can work, but it's not a sure thing for getting air out of the steel lines.....

' Not a sure thing' .... you really hate to tell him it is just not proper physics...don't you ? LOL

If you are not putting pressure behind the downward flow... then the release of fluid is going to coincide with the introduction of air from the bottom. There needs to be a reason for the air to not be able to rise inside the tube and be substituted for the fluid as the fluid comes out the bottom.... and some kind of pressure provides that.

vstech · #28 03-20-2011, 09:26 PM

heh, yeah that's true for sure. his method of sitting the hoses in the jar of fluid is NOT one of the methods of getting air out of a system.
the "gravity" method of flushing fluid from a MB system can succeed, but it will not get air out of the brake lines without luck. air wants to rise against the flow of liquid. and the bleeder does not flow enough fluid with only gravity to push against it to keep the air from rising. it will flow enough for changing flex lines, or changing calipers, but it's not a sure thing, and air can get into the steel lines with only gravity.
I have successfully bled the calipers, and flex lines with just gravity. but not on a car with ABS for sure.

Maki · #29 03-21-2011, 03:08 AM

As it happens, I was thumbing through my new Speedway Motors catalog today (did you get yours yet?) and came upon an interesting tool I'd never seen before: a reverse pressure bleeder. Has anyone tried one of these?

http://www.speedwaymotors.com/Phoenix-Systems-Reverse-Bleeder,48050.html

It would come in handy for those of us who work on cars that aren't German from time to time.

vstech · #30 03-21-2011, 08:36 AM

Quote:

Originally Posted by Maki

As it happens, I was thumbing through my new Speedway Motors catalog today (did you get yours yet?) and came upon an interesting tool I'd never seen before: a reverse pressure bleeder. Has anyone tried one of these?

http://www.speedwaymotors.com/Phoenix-Systems-Reverse-Bleeder,48050.html

It would come in handy for those of us who work on cars that aren't German from time to time.

see number four in post 26...