[W126 Coupe] Vacuum Tube Coding

[Dick Spellman]

Hi Dan,

I do not know of the color coding for the tubes but, have had to 
troubleshoot and replace a few of the vacuum circuits in the past.  
Basically you have the 3 or 4 vacuum take-off points on the motor.

Something like,
1.  The large brake booster line.
2.  The line to the emssions controls like egr, purge canister and air 
pump if any apply on the euro in your country
3.  The smaller line to the firewall valve and one-way valve and splitter
4.  The line to the vacuum modulator on the transmission.

It's the line at the firewall (#3 above) that you are concerned with.  
This should feed the vacuum resevoir in the fender and from there you 
have distribution to the various systems under the dash   Like the hvac 
distribution switching valve, the euro elevation lighting control in the 
dash and the seat locking solenoid.  You need to pull the IC and knee 
bolster to determine which color line is entering the cabin behind the 
IC and from there you will see their individual routing to the 
systems/devices.  You should be able to locate the seat solenoid valve 
which will have electrical and vacuum connections down in and near the 
steering column.  As I recall it gets hot so it is on the column clear 
of any material other than steel..  Again, it is controlled by either 
door pin switch which when door is closed, engine on; activates the 
valve so the vacuum to seat-back lock is positive.   When any door is 
opened or you depress the bleeder valve on the side of the seat,  the 
seat back locks are automatically released.

I'd guess you need to check the state change on the appropriate door pin 
switches to be sure the solenoid is being activated electrically then 
move on to a probable vacuum leak from the firewall to the solenoid or 
solenoid vac line to the seats.  Perhaps start with a check for voltage 
at the solenoid connector with engine on, doors closed, if voltage 
present, the solenoid is working. (as in open-allowing vacuum from 
engine to flow past the solenoid plunger and to the seat back locks.)  
Then check the vac line-in  to the solenoid for the presence of vac with 
engine on, if none, replace the line through the dash to the firewall 
valve and.or check the one-way valve at the firewall for damage.  If vac 
is present, solenoid is working (open) then vacuum should be pulling at 
the seat junction under each seat and seat locks should be active.  If 
not, then replace the outbound solenoid vac line to the seat junctions 
which runs in the under carpet plastic raceway along the floor by the 
door sills and comes up from the carpet under each seat.  Last, each pin 
switch can be checked with an ohm meter once isolated from the 
electrical ground circuit wiring.

Good luck,

Dick

On 10/12/2011 11:52 PM, L&D gardner wrote:

> Hi Folks

>

> Does anyone know of a circuit diagram for the colour coded vacuum 

> tubes,I am measuring 60kpa from the ivory tube from behind the engine 

> to the bulkhead junction ,and the seats will lock @ 15kpa with a 

> Mityvac at the same location on the bulkhead but the seats will still 

> not lock as I seem to be getting losses from the dark red and yellow 

> striped tube.Thanks

>

>

>                                                                             

>                                                     Kind Regards Dan 

> Gardner 1986 560 SEC (Euro 220kw)

> The MB Coupes Website!

> W126 SEC Mailing List

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