Mercedes-Benz Forum banner

Brake booster going out . What can I do and how long do I have?

4K views 10 replies 5 participants last post by  MBL87560SEC 
#1 ·
Pedal is going down to the floor while idling , very slowly .Took it to my local show and was told I need a new booster , about $1200 installed . I only bought the car with 300K on it for $2200 , now I have $3500 in it and really am not interested in putting much more in it . Is it ok to use a used booster? Where can I track down on the net ? What can I expect to happen ? I wanna hold out so I can get a C230 .
 
#2 ·
Hi 4amStudios,

I could be off base here, (but I really doubt it). In my opinion, as a former "Valvo" Tech, the real problem (IMHO) with your car is a BRAKE MASTER CYLINDER that is leaking internally.

The classic bad brake master cylinder symptoms would be the brake pedal slowly going away (towards the floor-ish) at a stop light or sitting in traffic, etc. This symptom would occur with NO external brake fluid leakage at all, just the unsettling feeling that the brake pedal was dropping while under a bit (or moderate) pressure.

If this is what your car is doing, I'd replace the Brake Master & flush NEW fluid to all four wheels.

Afterwards, I'd drive around a bit, to make sure..........

Then, take your MB for a really good cruise! BEFORE the Winter sets in!

It ain't the booster! (IMHO)

Regards, MBL
 
#4 ·
Would be inclinded to agree with 87560 going by your description. I have only ever seen a servo (booster) go once when the internals broke up but that was on a VW, and even then it went fairly dramitacally, rather than slowly like yours.

You can sometimes get away replacing the seals on the master for literally a few dollars and a spare afternoon if the bore in not scratched/pitted, but it may be easier and give you piece of mind to just renew the whole thing.

The master is also a great deal easier to replace than the whole servo unit.
 
#6 ·
Here is a link for a NEW Brake Master. $139. + shipping from AZ. Yes, it could be cheaper to rebuild....... but, if the rebuild fails for whatever reason, you'll end up with a new one anyway.

GermanStar is a supporter of benzworld. he has helped me out several times.

http://www.germanstar.net/126bp.htm

Cheers, MBL
 
#7 ·
Hey! same thing happened to my car! but i only spent Singapore $488.. Made a big difference in the braking feel. my mech said it was leaking or something.
 
#8 ·
Replaced the master cylinder with a new unit . Picked it up from the shop tonite . The pedal is tight as hell , they still think it's the booster . Some of you said that that is unusual . So what to do now ? Replace the booster or could it be something else ?
 
#9 ·
on your SD, first thing to check is the vacuum supply with a guage. a booster requires at least 20 inches of vac. to function properly. your sinking pedal was the master. that part seems solved. the hard pedal is a booster problem. if plenty of vac is there, then run the car, shut it down and loosen the 19mm line off the booster. the check valve in the line should retain the vacuum and removing the line should allow the booster to take a deep breath. (this should hold vacuum for days). if it doesn't, there's a problem. 1st, be sure the o-ring was installed behind the master cylinder. simply remove the 2 13mm nuts and pull the master off the booster. do not touch the lines. this o-ring is a must. if its there, look in the booster with a light. your master (old one) might have been leaking fluid into the booster. if it's full of fluid, you need a new one. the rubber diaphram in there can't handle the fluid. ps.. a leak at the booster will not allow the vac. pump to pull 20 inches.
 
#11 ·
Hey There 4am,

I'll bet the Doc is 100% correct. Perhaps the Brake Master leaked a volume of brake fluid into the booster. You really cannot compress the liquid........

The Booster rubber diaphragm, as BENZDOCstated, cannot deal with the B/Fluid OR a loss of vacuum.

At least the pedal doesn't go to the floor! Press On!

Good luck 4am, MBL
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top