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Vacuum check valve musings

Started by daantjie, 17 February 2023, 11:53 AM

daantjie

Hi guys

I have been experiencing loss of vaccum on my door locks whereas before it would hold vacuum for months.  I traced it down to the "secondary" check valve under the dash behind the cluster, the white/black one, part number 1238000078.  So I was wondering why we have this type of check valve in there as opposed to the blue/black ones, part number 1168300078?  These ones you will find all over the car, mostly you will see them in the engine compartment if you have the US spec ACC system, also they use them downstream in the ACC system as well.

Not sure if all 116's had this check valve in this location.  Also I think there might have been a supercession from the 116 to the 123 number.  I am pondering why this was done.

Anybody know why you cannot just use the blue/black ones under the dash?

Pics attached.

Cheers
[attach id=13733]1238000078.PNG
[attach id=13734]1168000378.PNG
Daniel
1977 450 SEL 6.9 - Astralsilber

daantjie

Just to add some context, here is a pic from one of Robert's (rumb) earlier posts:

Daniel
1977 450 SEL 6.9 - Astralsilber

rumb

I would suppose the insides are different and the behave differently.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS

daantjie

I might have to do an autopsy on the old unit to see what is what.
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

Quote from: daantjie on 18 February 2023, 01:36 AMI might have to do an autopsy on the old unit to see what is what.
I eagerly await your findings.  Got a similar problem.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

OK, time for show and tell kids ;D   I had to cut them open with my Dremel, they are very well stuck together, obviously as they need to be air tight.  The black/blue one seems to be more robust, with thicker vacuum diaphragm as well as a return spring of sorts.  The black/white one has a very thin diaphragm and a completely different design.  I know nothing of vacuum and such, so not sure what you guys make of this?

Daniel
1977 450 SEL 6.9 - Astralsilber

rumb

To late now but measure vac to open each one. Maybe top one is more of a regulator?




The top one  1238000078 is avail from dealer so just buy new one?
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS

daantjie

Yup I've got a new one on order.  I'll compare once it comes in.
Daniel
1977 450 SEL 6.9 - Astralsilber

Jenno1981

This was a timely post for me. I was making an attempt at diagnosing my central locking (or lack there of...) and located a broken Blue/Black.

Apart from the dealership, anywhere is Australia that would have these? Tried Bursons and Rare Spares but only got strange looks 🤷�♂️

Any local ideas?
1978 450SEL - Green
1999 ML430 - Also green 🤷�♂️