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  #1  
Old 07-28-2008, 08:20 PM
t walgamuth's Avatar
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Goofy brake problem 123

My trusty 240/300's brakes are acting funny.

Yesterday I discovered in the morning that the brake level was low. I filled up the rear res and decided maybe I have a leaky clutch slave. I have not noted any fluid running out but the pedal has been low and then high the same day. I thought it was fluid level somehow.

So today I let it run for about fifteen minutes with the ac running at idle while I went into my house and when I came out the pedal was tight up top and very hard and the brakes were dragging.

Now I am wondering if its a booster problem. Is the fluid escaping into the booser?

What do you all think?

Tom W

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  #2  
Old 07-28-2008, 08:37 PM
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If no fluid is visibly leaking anywhere and its disappearing then the booster is just about the only place it could be going....
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  #3  
Old 07-28-2008, 09:05 PM
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Though I've never heard of a bad booster causing the pedal to stay up stiff (not to be confused with just getting hard to push) and drag brakes, it does make sense that your fluid could be going in there if it keeps going down. Could it possibly be a sticking check valve inside the master or the proportioning valve perhaps?
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  #4  
Old 07-28-2008, 09:47 PM
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Is there a check valve? I am pretty sure there is no proportioning valve.

Tom W
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #5  
Old 07-28-2008, 10:14 PM
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With a gasoline engine that operates the brake booster off manifold vacuum, I have seen a faulty booster being the cause of Disappearing Brake Fluid Syndrome. I don't know how that would work on an MB diesel with its little vacuum pump. Wouldn't any liquid sucked in through the vacuum system get spit (spat?) out of the vacuum pump discharge? Wherever that is.
SEO
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  #6  
Old 07-28-2008, 10:31 PM
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Thats where my master cylinder leak was. Into the brake booster unit.
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  #7  
Old 07-28-2008, 11:10 PM
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Quote:
Originally Posted by seo View Post
With a gasoline engine that operates the brake booster off manifold vacuum, I have seen a faulty booster being the cause of Disappearing Brake Fluid Syndrome. I don't know how that would work on an MB diesel with its little vacuum pump. Wouldn't any liquid sucked in through the vacuum system get spit (spat?) out of the vacuum pump discharge? Wherever that is.
SEO
The diesel vacuum pump empties into the crankcase....so that'd not be a good thing if it was depositing brake fluid in there!
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'17 Metris(VITO!) - 29k - wifes (OC-34k)
'09 Sprinter 3500 Winnebago View - 61k (OC - 63k)
'13 ML350 Bluetec - 82k - dad's (OC-86k)
'01 SL500 - 98k(km) - dad's (OC-94,000km)
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  #8  
Old 07-28-2008, 11:29 PM
t walgamuth's Avatar
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So if that is it I could remove the vac line from the mc and find brake fluid in it?

Tom W
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..I also have a 427 Cobra replica with an aluminum chassis.
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  #9  
Old 07-29-2008, 12:19 AM
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only if you put a LOT of fluid in there... the lower portion of the booster holds more than the reservoir does...
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  #10  
Old 07-29-2008, 12:33 AM
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Tom, A several years ago I had a similar problem with a W123. Dragging brakes, stiff/high pedal. I could unbolt the MC from the booster and solve the problem. Measuring the protrusion of the booster to MC rod revealed it was slightly greater than another W123 I had at the time. No adjustment that I could find.
It was a wierd problem that would come and go and I never did figure it out. I eventually parted ways with the problem.

It had to be the booster as just about every thing else was replaced.
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  #11  
Old 07-29-2008, 05:39 AM
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Thanks, Dan.

Tom W
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #12  
Old 02-14-2009, 04:46 PM
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Tom- did you ever sort this out?

thanks...
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  #13  
Old 02-14-2009, 06:17 PM
t walgamuth's Avatar
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Indeed. It was leaking into the booster. I changed the mc and sucked as much out of the booster as I could and now all is well.
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #14  
Old 02-15-2009, 10:57 AM
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Thanks for the update- off to get a new MC.......
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  #15  
Old 02-15-2009, 07:48 PM
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What long term affects of leaving brake fluid in the vaccume booster ?
No way to get all of it out. will It deteriate the rubber diaphram in time?

I had this problem a few yrs ago, and replaced both at the same time fearing a problem later on.

Charlie

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