6.9 suspension light won't go out

[daantjie]

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.

Yup I agree.  Also the system in my experience does not react instantly during dynamic conditions.   There is always a bit of a delay where the valve catches up with the axle movement and then adjusts accordingly.   When front end dips then thereafter in my experience it will pump up more than is needed and then drop down again slightly as the valve adjusts to center.

Check it again at a red light, hard on the brakes, then observe the nose right after.  Mine always drops down a bit at the nose after a hard braking event.  Maybe mine is buggered too but this is how I have always understood the system adjustment to work.

[raueda1]

OK, ok, ok.  I'll go back to figuring out the light.  It makes sense that a red, glowing warning light is trying to tell me something, much as I hate to admit it.  I'll swap the pressure sensor (thanks Robert!) and see what happens.  I've been avoiding just cause it's a PITA.  So let's assume that doesn't help.  And recall, when I did all the other work I installed a spare pump instead of the original.  After the red light stuff I swapped the original pump back in, which had previously worked fine.  Didn't help, so I'm assuming (yeah, I know about "assume") that it isn't a pump problem.

Earlier Aaron proposed doing a systematic pressure check on everything.  I did look for a hydraulic pressure gauge kit but couldn't find one that seemed entirely suitable.  Recommendations welcome. 

Anyway, what else can cause low pressure other than a bad pump?  Some kind of fault in the regulator or up/down switch?  A stubborn speck of dreck on a ball valve seat?  And is it possible that low pressure would contribute to the dive issue?  This is slowly grinding me down.....   

[TJ 450]

Worn valves can cause a low pressure issue when they start bypassing internally. It's probably caused by wear between the disc and main body. I've had a valve fail in this mode. When it fails completely the car will either not raise at all, or will partially and the detents at the control disc will be weak as a result of the pressure loss.

Tim

[TJ 450]

It could indeed be that some dirt has entered a valve, but I would check everything else first including the o rings at the block/ main valve and all that stuff if not done already.

I'm sure you'll get to the bottom of it, but I would be surprised if it was the pressure switch.

The valves can be made like new @600 Air Suspension.com if it has to be done.

Tim

[TJ 450]

If any of that is the case they you will have a lot of fluid returning to the reservoir however.

Tim

[daantjie]

One thing I need to caution is to only work on 1x component of the system at any given time.  I have found that the HPF system, probably more than any other is EXTREMELY dependent on all components working in harmony.  So if you fiddle with multiple components at any given time, then you will never know which one gave you the condition in the first place, thus at the very least you will gain learning as you go, which then should make future problems easier to deal with.

In general the struts are the more robust component of the system, and faults usually lie with the pump, pressure regulator and leveling valves in my experience, in that order.  Of course your accumulators also need to be in good shape, that is always a given as baseline.

[Punker]

Hello, Dave,

in case you want to deal with the level valve: out of interest I disassembled it some time ago and then also overhauled it. Here are the links ( translate it with google or deepl):

https://www.w126-wiki.de/index.php?title=HPF-Höhenregler_überholen

The dimensions of the O-rings can also be found in the forum (or from me). After that the valve works fine. I have to say, however, that the car dives a little bit into my body when you brake hard. But stop only a little (noticeably). It is then within a fraction of a second up again or better on normal level.

Good luck.
Björn

[Punker]

If the link does not work: go to W126 Wiki, than to HPF than to "Höhenregler überholen". All information are there.

Björn

[raueda1]

Hello, Dave,

in case you want to deal with the level valve: out of interest I disassembled it some time ago and then also overhauled it. Here are the links ( translate it with google or deepl):

https://www.w126-wiki.de/index.php?title=HPF-Höhenregler_überholen

The dimensions of the O-rings can also be found in the forum (or from me). After that the valve works fine. I have to say, however, that the car dives a little bit into my body when you brake hard. But stop only a little (noticeably). It is then within a fraction of a second up again or better on normal level.  Good luck.
Björn

Hi Bjorn -- Thanks very much!  By coincidence I found that link and it's a gold mine.

Hi Everybody --  Minor update.  I just swapped the pressure regulator/switch assembly for another from a parts car.  That car rose properly but accumulators were shot and owner sold it after getting a US$15,000 repair estimate.  Anyway, it seems to be fully functional.  The nose dive question might actually be an improvement, but will need more driving to confirm.  Light is still on. 

So, to recap, 2 different pumps and 2 different regulator/switches all gave the same result:  working suspension but light stays on.  None of this is 100% conclusive, but the odds of all these elements showing the same symptoms strikes me as pretty small.  And that points more conclusively to the sensor itself.  I'll swap in a substitute later, I'm getting sick of messing with it.  Depending on the results I guess I'll have to find a pressure gauge kit.  Recommendations welcome.  Thanks and stay tuned....    Cheers,

[daantjie]

Dave I'm sure we've covered this (too lazy to read the whole thread ) but are you 100% sure your height control switch is adjusted to match your cable settings?  Pretty sure you have but might be worth another look.  The dash knob has 3 distinct "clicks" which should then have the corresponding control disk settings to match.  From memory some members have had to fine tune the cable to get it in the sweet spot to make the warning light go out in the "N" setting.

[raueda1]

Dave I'm sure we've covered this (too lazy to read the whole thread ) but are you 100% sure your height control switch is adjusted to match your cable settings?  Pretty sure you have but might be worth another look.  The dash knob has 3 distinct "clicks" which should then have the corresponding control disk settings to match.  From memory some members have had to fine tune the cable to get it in the sweet spot to make the warning light go out in the "N" setting.

Unfortunately yeah, in perfect adjustment.  I had to readjust slightly for the new regulator.  I'm going to drive it around a week or so to get a handle on it - ride quality, height, dive, etc.  Then

I did make an interesting discovery though.  My original regulator was from 1976 model year.  The filter has a rubber gasket on the top and bottom.  It's held together by a stout spring.  The newer one (1977) has no gaskets.  The filter just sits on the bottom of the valve held on by a screw/bolt/washer attached to a spring.  It can't possibly be as fluid-tight as the older design.  Quite odd.