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6.9 suspension light won't go out

Started by raueda1, 12 June 2020, 08:34 AM

raueda1

This is after replacing front and central spheres and uninstalling/reinstalling rear spheres (rear replacements not available).  I also replaced the large o-ring in the pump.  It doesn't seem to be leaking.  fluid level is good.  The suspension seems to work perfectly in every regard, though getting the car to rise again was challenging.  But the light simply won't go out.  I tested the light circuitry and it's fine (sensor illuminates light when sensor is connecting to ground when not under pressure).  Is it possible that the pump pressure is just slightly below the threshold pressure of the sensor?  Seems unlikely that the various repairs would do anything to the sensor itself.  What to look for here?  Help appreciated!  Thanks and cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

TJ 450

If everything seems to work fine, I would check that the knob/ cable are properly adjusted and the it's in the normal position. The light will stay on if it isn't.

1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

daantjie

Dave, check if you are getting return flow back into the tank, this would indicate that you have received cut - over pressure.
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

Quote from: daantjie on 12 June 2020, 10:36 AM
Dave, check if you are getting return flow back into the tank, this would indicate that you have received cut - over pressure.
Hmm, ok.  How do you do that?
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

Just look into the tank with a strong flashlight with car running, you should see a slow trickle of fluid coming into the tank via the filter once cut over has been attained.
Daniel
1977 450 SEL 6.9 - Astralsilber

daantjie

Also check the connection of the sensor on the 5th sphere, from memory I had a leak here when I changed my accumulators, after I snugged it up the light went out.  Sometimes there is some voodoo with the HPF system ;D
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

Quote from: daantjie on 12 June 2020, 11:12 AM
Just look into the tank with a strong flashlight with car running, you should see a slow trickle of fluid coming into the tank via the filter once cut over has been attained.
So if there is no trickle then cut over pressure has not being attained because pump can't reach high enough pressure to attain it?  That's assuming no leaks, which there aren't.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

Quote from: raueda1 on 12 June 2020, 11:38 AM
Quote from: daantjie on 12 June 2020, 11:12 AM
Just look into the tank with a strong flashlight with car running, you should see a slow trickle of fluid coming into the tank via the filter once cut over has been attained.
So if there is no trickle then cut over pressure has not being attained because pump can't reach high enough pressure to attain it?  That's assuming no leaks, which there aren't.

Correct.  Though to be clear that  trickle is very faint and you really need to look hard to see it, but if you do not have return flow then likely your pump is no bueno
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

Quote from: daantjie on 12 June 2020, 11:54 AM
Quote from: raueda1 on 12 June 2020, 11:38 AM
Quote from: daantjie on 12 June 2020, 11:12 AM
Just look into the tank with a strong flashlight with car running, you should see a slow trickle of fluid coming into the tank via the filter once cut over has been attained.
So if there is no trickle then cut over pressure has not being attained because pump can't reach high enough pressure to attain it?  That's assuming no leaks, which there aren't.

Correct.  Though to be clear that  trickle is very faint and you really need to look hard to see it, but if you do not have return flow then likely your pump is no buenoExcellent, thanks.  I'll report back with my findings in due course.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

UTn_boy

I'd pay more attention to what TJ450 says first.  The electric switch on the pull knob is notorious for either being out of adjustment or breaking.  That's not to discredit any of what the other fellas suggest. 
1966 250se coupe`,black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3,papyrus white/dark red leather
1975 450se, pine green metallic/green leather
1973 300sel 4.5,silver blue metallic/blue leather
1979 450sel 516 red/bamboo

raueda1

Quote from: UTn_boy on 12 June 2020, 07:59 PM
I'd pay more attention to what TJ450 says first.  The electric switch on the pull knob is notorious for either being out of adjustment or breaking.  That's not to discredit any of what the other fellas suggest.
Interesting point.  I'm quite certain that the cable is adjusted right.  But it gets a lot of use, probably more than it was designed for (my driveway has a huge dip).  By coincidence, I have a spare cable/switch out of a parts car.  The switch was "repaired" at some point by wrapping it up with electrical tape to hold it together.  I'm going to see if I can't get to the switch socket and rewire the system to take the switch out of the circuit so that it only responds to the sensor.  Thanks,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

I'm returning to this problem with some more info.  As noted elsewhere, the car is driving very well.  The ride is excellent and the suspension goes up and down as it should. 

I've been driving the car pretty gently.  In the back of my mind I had a growing suspicion that it dove more than it ought to, but I had hadn't stopped hard enough at speed to really be sure. Yesterday I did stop hard at speed and confirmed that on hard braking there is indeed very excessive nose dive.   No doubt at all, I'm 100% sure. 

So, can I safely assume that the front leveling valve isn't working right?  I had kind of assumed that the valves either worked or they didn't.  If it is indeed the front valve that means that it can work "somewhat" but not perfectly.  Kind of a surprise, if true. Maybe this would also account for the stubborn light staying on all the time.  Anyway, any ideas would be welcome.  I'll probably get too impatient in the meantime and just go ahead and swap it out to see what happens.  But I'd still like to know how the raising/lowering can work fine yet valve isn't correcting for dive.  Thanks as always, happy July 4th to the Yanks and cheers to the rest,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

UTn_boy

The leveling valves have nothing to do with whether or not the car nose dives on hard breaking.  What you're describing is indicative of bad accumulators, internally leaking rams, or air in the system. 
1966 250se coupe`,black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3,papyrus white/dark red leather
1975 450se, pine green metallic/green leather
1973 300sel 4.5,silver blue metallic/blue leather
1979 450sel 516 red/bamboo

raueda1

Quote from: UTn_boy on 05 July 2020, 02:54 PM
The leveling valves have nothing to do with whether or not the car nose dives on hard breaking.  What you're describing is indicative of bad accumulators, internally leaking rams, or air in the system.
Oh boy, thanks, I think.  But I don't get it.  Accumulators are new, in front anyway, so that's not it (or not likely).  Could be rams I guess, but this wasn't an issue prior to getting car back on the road so something had to have changed.  And I suppose there could be air in the system though I'd think it had bled out by now.  Guess I'll have to work harder to make sure it's purged. :P

Anyway, I just disconnected the front level valve connecting rod to check the valve and play around a little.  It seems to work as it should - F goes up and L goes down.  And "autoleveling"  seems to work.  If I stand on the bumper the car rises to compensate.  When I jump off it goes back down.  The rear does the same thing.  In fact it's kind of interesting how, when you pull up on the bumper it's easy to raise the car a bit but then you feel it getting heavier and heavier as it lowers. There is a small lag time, the system doesn't react instantaneously.  Maybe that's an issue, though there doesn't seem to be anything in the manuals about how fast the system should respond.  Should it respond instantly?  In any case, this does indeed suggest that the valve is working OK, right?

Still, I don't get how leveling valves would not impact dive if everything is working, at least if dive were long enough.  I mean, if the front goes down wouldn't that necessarily put the valve into fill mode to compensate?  That's essentially what's happening when you load the car up and the suspension auto-levels, except it's just happening in the front.  Maybe dive is too fast for the system to react?  I'm clearly missing something.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

I think you need to figure out why the dash light is on before anything else. Either you have a bad switch or too low pressure.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio