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  #16  
Old 03-21-2010, 02:31 PM
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It is not uncommon for a MC to "give up the ghost" during a routine maintenance procedure such as bleeding the system.

As described above, there is a normal operating area for the Master Cylinder (MC). If the seals are pushed beyond that area into a part of the cylinder that may have corrosion or deposits, the seals can easily be damaged.

Another premise here is that if the MC is going to potentially lose its ability to make pressure, it might as well do it during maintenance operations. I wouldnt lose any sleep.
Install a rebuilt unit and move on.

Another thing to consider is the one man bleeding system. Use a bottle, run hose from bleeder into the cap into the bottle. Be sure to loosen the cap during use to allow air to escape. Air will be displace as fluid enters the bottle.

With the car on jack stands, the operator can look under the vehicle at the (clear) hose going into the bottle. This allows the operator to not only see air bubbles if they exist, but also see the colour change and this know when the flush is complete. Close the bleeder and move to the next closest component to the MC.

Note:
It is helpful to use compatible fluids of different colours from one flush service to the next. (ATE blue and gold for example is what I use)
Use a turkey baster to remove all the old fluid from the reservoir before starting.
Do not push the pedal beyond the normal operating range while pumping.
No air will enter via the bleeder. Fluid flows OUT the bleeder simply by gravity.


Best of luck.
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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.
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  #17  
Old 03-21-2010, 02:41 PM
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Quote:
Originally Posted by Renntag View Post
No air will enter via the bleeder. Fluid flows OUT the bleeder simply by gravity. Best of luck.
Try pouring water out of a glass... it will flow by gravity... guess what will replace it ? AIR !!!
If your threads on the bleeder nipple are not air tight... air will enter the system... this is not even a serious question as to the physics.... see the other threads concerning this...
Some might accidentally be air tight... but sometimes people quit without all the air bubbles out of their system and do not realize it...
When the pressure required to suck the fluid out of the bottle exceeds the pressure required to pull air by the bleeder threads air will enter the system.
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  #18  
Old 03-21-2010, 02:52 PM
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Over 20 years of vehicle maintenance and racing championships were all just luck then.

As fluid pushes out the bleeder air will not enter. Your suggestion, defies my understanding of physics. Sorry man. Not buying it. In the course of ONE season of racing, I will effectively have bled the brakes enough times on our cars to just about service a large portion of the street driven cars on this forum. OK, a bit of an exaggeration, but experience by volume none the less.
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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.
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  #19  
Old 03-21-2010, 03:00 PM
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Originally Posted by leathermang View Post
Try pouring water out of a glass... it will flow by gravity... guess what will replace it ? AIR !!!
.

Ok, so lets use your example. Taking a look at our hydraulic system like your glass/water example.

I am suggesting that having an open bleeder will not allow air to enter the system as this is what we call "gravity bleeding."

You are correct, as fluid is removed from a container, if the container is not decreasing in volume, either by a plunger or wall moving, or by the container being deformed, air must enter. But alas, with the cap OFF the reservoir, you have created a way for air to enter.

With out the cap removed, some systems use rubber on the back side of the MC cap that will deform, taking the place of the missing fluid while NOT allowing moist air into the system and thus contaminating it.

Systems that allow air to enter the MC as level changes, I believe should be flushed more often as that exchange of air allows water to enter the fluid. Brake fluid absorbs water.
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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.
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  #20  
Old 03-21-2010, 03:01 PM
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Maybe we should just link this to the previous debate and get back to trying to help the OP. Does he have a MC issue or a bleeding issue? Not sure as he used a bleeding method unfamiliar to us. I'd suggest he redo the bleeding following whatever endorsed method he likes. If he doesn't succeed, I'd replace the MC.
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1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html
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  #21  
Old 03-21-2010, 03:08 PM
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I dont think his method was poor or inadequate. I only question that in his description he doesnt mention "pumping" the brakes but rather:
Push pedal
open bleeder
close bleeder
release pedal
repeat.

A pumping action would build pressure.

I also believe that if the pedal was pushed too far down that the MC may have been compromised.

I think we are all in agreement on this possibility.

How much is a new MC?
how long to install?

If the answers to both of those are small numbers then the solution is clear.
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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.
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  #22  
Old 03-21-2010, 03:11 PM
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http://catalog.peachparts.com/ShopByVehicle.epc?q=&yearid=1983@@1983&makeid=63@@MERCEDES+BENZ@@X&modelid=6207%3AMBC|1510%3AED|10000134@@300SD&catid=241658@@Brake&subcatid=241705@@Brake+Master+Cylinder&applicationid=W0133-1616041&mode=PA

New MC from Fastlane is approx 140$.
2 listings based on chassis Number.
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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.
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  #23  
Old 03-21-2010, 03:14 PM
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Agreed. He didn't pump. He had the engine running to use the power assist (that's the part I've never heard of doing).

I don't know the cost of a MC without checking and I'd replace it as I never compromise safety (stopping power); but some of the forum members are scrapping pennies to keep their cars running.
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  #24  
Old 03-21-2010, 03:15 PM
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All Parts Express is about 60$ for this unit.




I would also mention that 700ml of fluid isnt "too much" for a flush IMHO.
I would expect to go through at least 946ml performing a flush/bleed.
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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.
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  #25  
Old 03-21-2010, 03:23 PM
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Quote:
Originally Posted by Renntag View Post
As fluid pushes out the bleeder air will not enter.
You are not reading close enough.
it will not enter as long as there is pressure pushing it out.. but that is really not gravity bleeding either... that is pressure bleeding... by the MC...
but once pressure is not being applied and you try to use suction from that bottle mounted at the tube from the bleeder nipple...
Then you have a huge , even probable , air into the bleeder situation.
I am saying that the bleeder nipple needs to be closed while positive pressure is being applied to the system...
IF GRAVITY is allowed to enter the equation... meaning you halt the brake pedal travel.. even if you do not allow it to return and suck air in... that GRAVITY escape of fluid from the bleeder will be replaced by air.
Opening the fluid container of the MC does not affect this sitation down at the bleeder ... it only allows fresh fluid to enter the pressurized system after the pedal is allowed to resume its resting position. So if you allow it to return before closing the nipple air will be sucked in... if you do not close the nipple while positive pressure is on the system fluid and any drops out by gravity then it will be replaced by air.
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  #26  
Old 03-21-2010, 08:25 PM
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Whoa! Didn't know I'd stir up such a controversy!

Renntag I think is on point here. The method I've used to bleed the brakes is pretty common, as I just looked up the most common information on the 'net I could find and put it to work. I asked my uncle who's a mechanic and he said the same thing. I definitely had the helper pump up the brakes before we started. However, through all of this I have been holding the bleeder valve open until after the fluid stops coming out.

I'm just about to go give it another try at all four wheels and we'll see where I'm at after. At this point I'm just a little leery to go out and buy a MC on a hunch if it's still just air in the lines. I'm already short on time and money these days as it is, and this has eaten up pretty much all of my spare time for two weekends and a couple of weeknights now. Parts aren't cheap up here (about $200 for the MC) and I already spent over $200 for the new caliper and two used ones off of CL that were NFG. Add in another $200 or more in gas driving 600 miles in the truck this week instead of the car... (I haaate gassers!) and I'm out a fair chunk of change. Could'a taken it to a mechanic for that kinda money...

C'est la vie...
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1981 300SD - 283,000 KM's at purchase, 360k+ now. Engine replaced at 311k. 16" CLK wheels, w126 gen II cosmetic upgrades, late w126 leather interior. Parting due to fire

1987 300SDL - 243K miles and counting. Just getting started!

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  #28  
Old 03-21-2010, 09:06 PM
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Originally Posted by destroy View Post
Parts aren't cheap up here (about $200 for the MC)
Didnt I provide a link to a 60$ MC above? Throw in some fuel/oil filters and what not and hit 100$ and you get free shipping !

Let us know how the additional bleeding works out.
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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.
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  #29  
Old 03-21-2010, 09:36 PM
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Quote:
Originally Posted by Renntag View Post
Didnt I provide a link to a 60$ MC above? Throw in some fuel/oil filters and what not and hit 100$ and you get free shipping !

Let us know how the additional bleeding works out.
You're right, but the problem is I live in the pacific northwest, in Canada no less, and I need this part ASAP. Even if by some rare chance they get out of the door from the place they're ordered from in a timely fashion, things can take a bit of extra time to ship here sometimes from the other side of the line because of the time in customs (UPS/FedEx etc usually is faster because they don't sit in customs), and on top of that AllPartsExpress doesn't ship to Canada and my passport isn't valid currently so I can't go pick it up from my depot in Washington.

I just started with the back brakes and after a few bleeds on the valve there's nothing coming out of them. Before I noticed that the reservoir has two sections kinda, and the front section was still full of dirty old fluid. Now that I'm not getting anything out of the back, that front section of the reservoir is empty and the regular part is still full. Is there something I should know here? The car is still up on stands but the pedal feels soft and wrong now. No pumping or anything seems to be circulating fluid or making a difference.
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1981 300SD - 283,000 KM's at purchase, 360k+ now. Engine replaced at 311k. 16" CLK wheels, w126 gen II cosmetic upgrades, late w126 leather interior. Parting due to fire

1987 300SDL - 243K miles and counting. Just getting started!

2001 Ford F250 Super Duty "Platinum Edition" Lariat 4x4 7.3L turbo diesel, 260k+ miles, various small mods.
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  #30  
Old 03-21-2010, 09:59 PM
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The bleed method I was taught way back involves much the same as others have suggested: put a hose (preferably clear) on the bleed nipple and submerge the other end in a container with enough clean brake fluid to cover the tip of the hose so that no air can get back in, pump the pedal 2 or 3 times and hold it down, open the bleeder and let the pressure out, close the bleeder before releasing the pedal, and repeat until no bubbles, emptying the container as needed, and keeping the MC topped up with clean, fresh brake fluid. Never reuse fluid that was in the system.
The theory behind pumping the pedal is to pressurise the system, forcing the air into solution with the fluid so it will travel with the flow, so an air bubble is less likely to hang up in a union or high spot in the line, or such was the explanation I was given.
As far as the engine on / engine off question, that may be mentioned in the FSM. For example, the Kia FSM for non-ABS power brake systems says to bleed the brakes with the engine idling, which I thought was odd, but that's why you refer to them.
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