Servo brake booster

[Ian45]

During a recent engine overhaul I stripped the whole engine bay and resprayed it. Amongst other things, I removed the servo. I've put everything back together and the engine is running fine. The only problem I have is that the revs increase by 5-600 rpm when I press the brake pedal !

I have checked that the one way air valve is fitted correctly and is working so most people I have spoken to are saying that the servo diaphragm has probably failed. A friend has let me have a second hand servo but it's from another MB model, not a W113, so the rod protruding from the rear of the servo does not have the ball end that goes into the socket inside the alloy casting. Instead it is designed to connect directly to the brake pedal. It may be from a Fintail. Otherwise the two servos are identical.

My question is - can the two different rods be swapped ? Alternatively, can my servo be overhauled or are they totally sealed and designed to be replaced as a complete unit ? Because the 113 servo is unique to that model I will struggle to find a good replacement used one here in the UK and they are expensive to buy new.

[glennard]

Sounds like you not only have brake problem, but an idle one, too.  Enough fuel to idle at 1300 rpm!  Disconnect the FIP rod, then slowly open the butterfly.  If rpms go to 1300, you're really rich.  Stop engine and 'click back' the pump.

[Naj ✝︎]

Hello, Ian,

I believe your servo is not unique to W113s but to RHD cars.

You may be able to source one from a UK W108.

Seems like they are unique to RHD 113s (000 430 5630)

naj

[waqas]

quote:Originally posted by naj

You may be able to source one from a UK W108.

I'm not sure if there's any difference between early and later 108s, but the later 108s use a booster that's too large (I believe the diameter is larger than the 113s). I've actually tried out one of these boosters in a 113 and it just barely touches the hood when closed.

The 111 (fintail) booster is identical to ours and can be interchanged directly.

I had my booster rebuilt a couple years ago for about $160 plus shipping from Power Brake Exchange in San Diego. Perhaps you can find a rebuilder somewhere in the UK?

[waqas]

quote:Originally posted by naj

I believe your servo is not unique to W113s but to RHD cars.

Naj, do you know what exactly is different about the brake booster in LHD vs. RHD cars?

[Naj ✝︎]

quote:Originally posted by waqas

quote:Originally posted by naj

I believe your servo is not unique to W113s but to RHD cars.

Naj, do you know what exactly is different about the brake booster in LHD vs. RHD cars?

Yes, Waqas,

The LHD servos have a yoke at the end of the operating rod. RHD's just have a ball end.
Dont know if there is enough length on the LHD rod to allow cutting off the yoke and grind the rod suitably.

Picture of RHD servo:



naj

[halman2228]

Holy Cow Naj!

How do you come by all this detailed information?

And don't quit! I'm sure you're saving a lot of us untold grief  when figuring things out!

Best regards,
Kevin

[Naj ✝︎]

quote:Originally posted by halman2228


Holy Cow Naj!

How do you come by all this detailed information?

And don't quit! I'm sure you're saving a lot of us untold grief  when figuring things out!

Best regards,
Kevin

Thanks, Kevin, [:p]

Most of the pictures and a little knowhow are from my ex 230SL I did 'some' work on  :oops:   :? . The rest I learnt from guys on this site...

naj

[Ian45]

Thanks Naj. I am nervously considering attempting to cut the two ends off and having the ball welded on to the other servo. Bit worried about the heat damaging the internal seals on the servo.

[Benz Dr.]

I found out something today that might be of interest.

I'm working on a 250SL and the brakes keep locking up - all four of them. The car moves OK when it's cold and sometimes it's OK for longer drives or it will lock up in less than a mile. The fact that it locks up at all isn't good.

So, I movede the adjuster at the back of the booster - no change and only got worse. All new parts in the braking system so no problems there..... humm.... what could it be?

Turns out it has a 280 SL style booster with a 230SL style master cylinder. They don't work together. The  280 push rod is too long inside of the booster for the early master. Go figure.....

[waqas]

quote:Originally posted by Ian45

Thanks Naj. I am nervously considering attempting to cut the two ends off and having the ball welded on to the other servo. Bit worried about the heat damaging the internal seals on the servo.

I wouldn't do that if I were you. There is a large rubber diaphragm inside the booster that will very likely get damaged. See if a local booster rebuild shop can take the two apart and swap the push-rods for you.