Author Topic: Another 6.9 suspension light question  (Read 514 times)

raueda1

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Another 6.9 suspension light question
« on: 26 July 2021, 07:41 PM »
A year ago the front spheres and central spheres were replaced.  Thereafter the suspension worked perfectly but the suspension light never went out.  FWIW the suspension worked fine before the sphere replacement.  I did it just because.

Recently I rebuilt all the struts along with replacing the rear spheres.  That's another story, but the outcome was excellent.  Ride remains excellent, though a bit firmer which is actually better.  No dropping at all despite 30 degree day/night temperature swings.  Last but not least I replaced the system pressure sensor.  The old one seemed to be shorted hence light was always on.  Now the light is out!  And it's always out.  Even if the car is started cold after sitting several days it never comes on - but there's also no suspension drop at all.  Wonderful!!  So maybe it's all perfect.  But the light will come on in the raised position but that's because of the dashboard switch.

So how does it all work exactly?  It would be great if the light is staying off cause there's no pressure loss and corresponding pump-up.  But is it possible that the replacement sensor is failed in an open (light off) position?   The light coming on in the high position doesn't count cause its the switch in the pull-knob.  So how do I know I everything is now perfect or if the new sensor is always open?

Doesn't everybody love this stuff?  Comments welcome.  Thanks and cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

UTn_boy

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Re: Another 6.9 suspension light question
« Reply #1 on: 27 July 2021, 02:22 AM »
If the car isn't dropping overnight or over several day/weeks then it would be normal for the sensor not to turn the light on......because there is no pressure drop.  I suppose of you wanted to test the switch you could open one or more of the bleeder valves, allow the system to depressurize, and then see if the light comes on.  Afterward, start the car, allow it to rise again and see that the light turns off. 

Otherwise it sounds like everything is working normal.  The light rarely came on to start with, especially when new.  Only a loss of internal system pressure will cause the switch to turn the light on. 
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tcj

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Re: Another 6.9 suspension light question
« Reply #2 on: 27 July 2021, 07:06 AM »
to be exact: the pressure that is checked by the pressure sensor may drop to 0 bar without the car is going down.
So in turn the fact your car stays up does not indicate that the pressure sensor sees >100bar (this is the limit for the switch on a 6.9).

To check the light without loosing oil:
- push in the knob above your steering wheel to its normal position
- remove the wire cable from the switch disc at the regulator
- turn the switch disc anticlockwise to the last position

This will route all oil in the support system back to the tank and the pressure sensor will see 0 bar which should enlight your lamp.

Now start the engine and note how long it takes at idle speed until the light is switched off
-->if this happens at idle within 1-3min your pump and your regulator works fine.
-->If you need higher revs to switch off the light there is room for optimization...
Regards,
Thomas
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daantjie

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Re: Another 6.9 suspension light question
« Reply #3 on: 27 July 2021, 08:05 AM »
Not to be too nit picky, but in my experience the system should fully pump up in max 1 minute from completely flat.  3 minutes to pump up would be way too long in my opinion.  Agreed no revving should be required, the system should pressurize easily under idle revs.
Daniel
1977 450 SEL 6.9 - Astralsilber

tcj

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Re: Another 6.9 suspension light question
« Reply #4 on: 27 July 2021, 08:18 AM »
Hello Daniel,

agreed - but if it takes 2-3min at idle I would not put time or money into the pump and regulator to go back to 1min. I think 2-3min are still ok and acceptable.
Many cars out there need higher revs, so this is what should be optimized.

Just my opinion.

Regards,
Thomas
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