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  #31  
Old 02-26-2010, 10:25 PM
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Join Date: Oct 2005
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I got a Motive Products bleeder. It's basically a weed sprayer with a spare master cylinder cap, but it's enough nicer than what I would make that I paid them for one.

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  #32  
Old 02-26-2010, 11:22 PM
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Join Date: Dec 2009
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WHOA, Whoa there. lets not have this thread become snippy. if people want to bicker or act self righteous take it to another thread. that is not advice. I did not ask for help or advice on bleeding. my question was very simple if you care to read it. Please be more careful when responding so that the advice you give is worthwhile. So that 4x4 and leathermang dont get off track i will address your comments one by one.

from leathermang-the viscosity of air is so much less than that of brake fluid... it can be sucked into the system at the threads of the brake bleeding nipple.
from 4x4-Speed bleeders are very different, they seal but have a check valve built in.

leathermang- take time to understand what i wrote before you respond. im not trying to dismiss your idea. however speedbleeders and a regular bleeder hooked up to a reservoir that will only allow new fluid to be sucked back in effectively function in the same way and according to your idea will also introduce air through the threads. as i stated, my experince with speed bleeders has been positive, with no air introduced through the threads. furthermore, as i already stated i only don't close the bleeder when im FLUSHING out the old fluid. after that i BLEED them(flushing and bleeding are different), closing the nipple every time before the pedal is released.

4x4 your statement about them being different is in this case irrelevant. As you state, the problem occurs at the threads, which are the same on regular and speedbleeders. I will say that most speedbleeders i have used have a thread sealing compound on them to prevent the air leakage that you mention and that i have expernced when vacuum bleeding. i tried to include a link to permatex high temp thread sealnt(brake fluid safe) but it wouldn;t let me. it might work to eliminate bubbles from vac bleeding.
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  #33  
Old 02-26-2010, 11:36 PM
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back to the matter at hand. when i removed the m.c this afternoon i found the booster had a lot of fluid in it. the rear seal of the m.c must have been bad, since that seems to be the only way for fluid to get in the booster. i took the mc apart hoping to find something obvious that would cause the seal to fail. there was no rust in the bore and the rear seal and rear piston cup looked fine. this is my question. #1 Do the seals just wear out with age? #2 it seems like that if you push the piston in up to the stop fluid could come from the farthest back port of the m.c. and leak out into the booster. could this have happened because my helper pushed to ahrd on the pedal while bleeding? doesn't seem right but then again the seal looked fine so im trying to figure it out. thanks for your patience
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  #34  
Old 02-27-2010, 12:32 AM
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You don't want to use an actual thread sealing compound on the bleeders, the seal is at the angled face. The material used on the speed bleeders is different and is to prevent the air from getting sucked back in.
The seals do wear, that is what changes the color of the brake fluid. The dark stuff is rubber dust suspended in the fluid.
If you remove the pistons from the MC, and clean the bore with a spray of brake cleaner you can see the corrosion. You may need a bright small light like a compact little LED, but it's usually pretty obvious. An aluminum MC will have a white powdery stuff in it, aluminum oxide, a harsh abrasive.
If there's fluid in the booster then the seal is not fine no matter how it looks.
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  #35  
Old 02-27-2010, 12:51 AM
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Location: Woolwich, Maine
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Guys,

Air leaks in past the bleed nipple threads if you leave the bleed nipple unseated and lift the brake pedal. Unless you liberally coat the bleed nipple threads with a heavy anti-seize lube. In the old days, before I had sons who could help, I developed a detailed procedure for changing brake pads on W123's as a completely solo operation and posted it here. It was a one man operation because, at the time, that is how I did it out of necessity. I still coat the threads with a load of NAPA high temperature anti-seize with aluminum, but I now take advantage of help from the boys, now grown up and becoming decent mechanics themselves. Getting that stuff all over the threads helps prevent stuck bleed nipples, which can lead to broken off bleed nipples, which, besides sounding painful usually leads to more parts and work than I typically plan for when I change pads.

A standard part of any brake service should be a flush and bleed of the brake fluid. It is cheap stuff (I use Castrol-GTX LMA, which is available at most NAPA or other outlets and it is DOT4 - costs me about $6 for two cans and I rarely need more than one) and changing it regularly keeps corrosion down, and thus the dispersion of corrosion particles. It does not take much to damage a seal in a master cylinder or one of the seals in the caliper. So, while there are different terms for the process - flushing and bleeding - they should actually be considered phases of the same task. And, if you flush like you bleed, you don't have two separate operations. I typically bleed until the fluid coming out of the caliper on the particular brake is clear, clean and without bubbles. You need to make sure both chambers of the fluid reservoir are filled when you start, and then when you have bled about half of the volume of one chamber, you refill.

If the brake fluid is really old, then the chances of having a master cylinder failure due to seal abrasion caused by corrosion is higher as you run the pedal to the floor. If you change it every two years, or sooner, that just won't happen in my experience. Worth the $6 max it costs every two years or so as I do the math.

Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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