Goofy brake problem 123 - PeachParts Mercedes-Benz Forum

t walgamuth · #1 07-28-2008, 08:20 PM

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

pawoSD · #2 07-28-2008, 08:37 PM

If no fluid is visibly leaking anywhere and its disappearing then the booster is just about the only place it could be going....

Mustang_man298 · #3 07-28-2008, 09:05 PM

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?

t walgamuth · #4 07-28-2008, 09:47 PM

Is there a check valve? I am pretty sure there is no proportioning valve.

Tom W

seo · #5 07-28-2008, 10:14 PM

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

Ara T. · #6 07-28-2008, 10:31 PM

Thats where my master cylinder leak was. Into the brake booster unit.

pawoSD · #7 07-28-2008, 11:10 PM

Quote:

Originally Posted by seo

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!

t walgamuth · #8 07-28-2008, 11:29 PM

So if that is it I could remove the vac line from the mc and find brake fluid in it?

Tom W

vstech · #9 07-29-2008, 12:19 AM

only if you put a LOT of fluid in there... the lower portion of the booster holds more than the reservoir does...

Whiskeydan · #10 07-29-2008, 12:33 AM

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.

t walgamuth · #11 07-29-2008, 05:39 AM

Thanks, Dan.

Tom W

mobetta · #12 02-14-2009, 04:46 PM

Tom- did you ever sort this out?

thanks...

t walgamuth · #13 02-14-2009, 06:17 PM

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.

mobetta · #14 02-15-2009, 10:57 AM

Thanks for the update- off to get a new MC.......

charmalu · #15 02-15-2009, 07:48 PM

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