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W220 S320 CDI 2005; W140 S280 1994 (Sold Nov. 2012)
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Discussion Starter #1 (Edited)
My brake pedal has squeaked or groaned on and off for years. Initially, it drove me mad and I sprayed/oiled the cabin-side of the linkage and booster with a range of stuff to no avail: others have tried the same. I learnt to live with it - but suddenly my wife has become aware of it which has made it a 'nuclear' issue.

One of the contributors to the threads on this topic paid a few hundred dollars and changed his brake booster: this was also the solution offered by my M-B main dealer, a route I'm not keen to pursue without a fight.

I looked at a cross-section of the booster/master cylinder assembly and realised that there are a lot of moving parts on the far side of the booster. I disconnected the vacuum connection and sprayed some dry PTFE lubricant inside the booster but this seemed to make no difference. So I backed off the two nuts holding the booster on to the master cylinder, slid the master cylinder forward until there was a small gap and gave it a couple of shots of a light lubricant ('3-IN-ONE with PTFE'). In 11 journeys since, I haven't heard a groan - and the brake pedal's quiet, too.

Mike
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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you are lucky.

i paid 2500 EUR for several "repairs" of my HVAC and non of them fixed vibrations of the blower. Finally I put a 2 x 2 cm piece of foam rubber under the plastic housing which holds the blower (with 4 screws) and since then all is ok.
 

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SL55, 300SE, GL450, Daytona 955i
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If you can add few pictures with explanation, you ll be the first to resolve this issue...

Thanks for the effort...
 

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W220 S320 CDI 2005; W140 S280 1994 (Sold Nov. 2012)
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Discussion Starter #5
If you can add few pictures with explanation, you ll be the first to resolve this issue...
The first pic is an illustration of a brake booster with the region where I think the noise is coming from circled in yellow, i.e. the engine side of the bulkhead. I didn't take pics while doing the job so I've annotated some that I've taken of the normal assembly.

To get access to the nuts retaining the master cylinder you need to remove the air intake and unscrew the vacuum hose connector. Then loosen the two nuts retaining the master cylinder against the face of the booster - I just took them to the end of their threads without removing them 'cos I'm not sure what's inside there. I then slid the master cylinder forward, producing a small gap between it and the face of the booster. I injected a couple of shots of lubricant spray in this gap.

Still no noise today - but if it comes back in future, I'll let you know.

Mike
 

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W140 Mercedes 500 SE, 1992, European, 410.000 km
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excellent. i hardly wait for my brake cylinder to start to "sing" :) ... just to use your recipe.
 

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W220 S320 CDI 2005; W140 S280 1994 (Sold Nov. 2012)
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Discussion Starter #8
So did it work for you too?

Anyone else try this?

I'm going to try it this weekend. I will keep everyone updated.
My brake pedal is still 'squeak-free'.

Btw, when I did this job I assumed that there was a non-return valve for the vacuum line to the booster inside the booster. But when I looked subsequently and traced the black vacuum connection back towards the inlet manifold, I found a non-return valve in that line, quite near the manifold. This leads me to think that it may be possible simply to undo the vacuum connection on the booster (large hex nut) and inject a small amount of lubricant spray straight in - a very much easier job.

See what you think.

Mike
 

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M20
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My brake pedal is still 'squeak-free'.

Btw, when I did this job I assumed that there was a non-return valve for the vacuum line to the booster inside the booster. But when I looked subsequently and traced the black vacuum connection back towards the inlet manifold, I found a non-return valve in that line, quite near the manifold. This leads me to think that it may be possible simply to undo the vacuum connection on the booster (large hex nut) and inject a small amount of lubricant spray straight in - a very much easier job.

See what you think.

Mike
Awesome info Mike (added to knowledge base)

Can you give another diagram of what you just said ^ :rolleyes:
 

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W220 S320 CDI 2005; W140 S280 1994 (Sold Nov. 2012)
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867 Posts
Discussion Starter #10
The first pic is the nut connecting the vacuum line to the booster. When I first tried this job I did put a small amount of lubricant straight into the booster after undoing this vacuum connection. It didn't get rid of the squeak and I didn't pursue this because I knew that there had to be a non-return valve and assumed it was inside the booster.

I have now identified the non-return valve as being in the vacuum line over by the intake manifold (pic 2) so I wonder whether a more sustained injection of lubricant spray straight into the booster would fix the squeak: I don't know but it would be an easier job than the albeit successful method I finally used and detailed in my first post.

Mike
 

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'95 S320
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UPDATE: Sorry. I did do this and I haven't heard that groan in ages. I shot PB blaster into the brake booster through both openings (vacuum hose and partially separated brake booster). No more GROANING!!
 

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Correct ! Just removing the vacuume line and a lil lithium grease squirt did the trick. No more embarassing whuooosh every time you hit the brake. Bravo !!
 

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W123 230E, W140 S320, W202 C220
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Wow! Also correct from here. I have been driving my W140 S320 for 8 years with this annoying groan, and after squirting some lithium grease through the vacuum line connection the brake pedal groan is gone!
 

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E500(1993) E220cdi(2004) SL500(1994)
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271 Posts
Hi.
Does silicon spray work in this case too??
I have this horrible groan/squeak most of the time when pressing the brake pedal even though I already replaced the booster with a very good used one. The noise is less but still present!
I would like to go ahead and try spraying lube into the vacuum line connecting hole. I have WD40 / Z Lube Cyclo / Liqui Moly silicon spray. I always have them in my tools box and wanna know if one of them would work succesfully in lubing the internal of the booster...
Thanks guys!
 

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00' ML55 AMG, 98' E430, 95' S320
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I would think any of those should work. If it doesn't no harm done.
 
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