740iL with SLS rear suspension - sags/relaxes at rest with engine off (no leaks)

[Legoman]

Just wondering, is it normal for the self-leveling suspension in the rear of a 740iL (SLS shocks only, no EDC), to slowly 'relax' and sink down after a couple of days sitting with the engine off and no additional weight in the boot besides a full (100 litres) of fuel in the tank?

My car does this post full rear Sachs SLS rear shock rebuild with all refurbished mechanical control valve assemblies. There are absolutely no leaks to atmosphere in the system. PAS reservoir is almost over-full and has not moved since shock rebuild nearly 6 months ago. I'm wondering if perhaps I might have a leaking non-return valve in the system somewhere that is allowing fluid to leak back to reservoir from the statically loaded shocks when not being pumped up by the running engine/PAS pump.

Are the shocks supposed to maintain the static pressure they held before the engine was switched off, or is the system meant to 'relax' and gradually sink down while the engine is off to be held on the spring height alone?

[unity]

Are the accumulators new? I had a similar issue with the rear dropping, except it would happen faster. It would always level up. I suspected the regulating valve but I knew my accumulators were shot. Well eventually I did the accumulators as a matter of need. A member here mentioned doing so solved their sag issue. Well, it did for me too.

My theory is that if the accumulators are shot, they of course are full of solid fluid. And I think even a good system does have leaky-by somewhere. So if there is just fluid in the system and a slow leak, the car drops. But with good accumulators one has a source that can compensate, as fluid pressure drops the accumulator bladders expand compensating a bit. Granted I think there is a limit to this too, maybe a week, etc. Again, just a theory as they were the only thing I replaced and never had sag now, even with extreme temperature drops.

[Legoman]

The accumulators were last renewed about 8 years + 65,000km ago. I'm guessing it might be reasonable to assume they are due for another replacement? There is absolutely no leaking on the garage floor, but the internal membranes between the nitrogen & the Febi-Bilstein fluid could be gone. How do you diagnose if this is the case from installed in the car? The ride in the rear is not silky smooth that's for sure, but I was rather putting this down to a side effect of the relatively new (to the car) Continental SSR run-flat tyres I had to put on after swapping to E38 style 61 16" wheels recently. I've never driven on run-flat tyres before, so not sure what degree of harshness is reasonable to expect with such stiff side-wall tyres. Certainly they are harder than the cheap no-name Chinese brand 15" tyres it was on before.

How did you know your accumulators were shot? I have no problems here with extreme temperature drops. It never freezes or snows here.

[unity]

I knew mine were shot due to the harsh ride. And that fact that they were factory original. The only way to test that I know of is to remove the lines and insert a blunt object to see if you can press on the bladder. If the object goes in far/pushes easily then the bladder is shot. As for run-flats, mine are actually smoother than my previous set. I have 18" E65 wheels with Pirelli P7 run flats now and the previous set was Pirelli P6 regulars.

[shogun]

Another possibility is that the regulating valve for LAD, usually when the LAD level is correct, the valve should be at zero position = the valves closed. In that case you can push a screwdriver or similar thru the lever on the regulating valve into a hole of the regulating valve.
In case it is not in zero position, the Pentosin can flow back into the reservoir from the shocks/bombs.
There are 2 valves inside the regulating valve.
Control Valve
The rotary control valve located on the rear suspension has three positions:
• Raise
• Level
• Lower
The control lever is attached to the rear stabilizer bar to sense vehicle loading. When the vehicle is loaded (passenger or luggage) the suspension drops and the stabilizer bar twists.
The control lever is moved in the "raise" direction.
With the engine running, oil flows from the pump to the bottom of the rear struts. The body of the car is lifted and the control lever returns to the level position.
In the level position, the oil bypasses the valve and returns to the reservoir through the return line.
A minimum pressure of 440 Psi (30bar) is maintained at all times. If service is required, a bleed off valve is installed on the control valve to drain the systems pressure.

see pics on my website under systems>>LAD http://twrite.org/shogunnew/topmenu.html

[Legoman]

Yeah I've seen the control lever assembly on the rear stabilizer bar when the car was up on hoist in the workshop. Complicated little system. I'm not overly concerned about it right now. I suspect it might just be the sheer weight of a full tank of fuel. I don't normally completely fill it because it has the V12 100 litre fuel tank and that's a lot of weight to be pulling around on city streets constantly accelerating + braking in a city completely overrun with too many traffic lights. When the fuel load has dropped down to about half, the suspension no longer so obviously sinks down over time with the engine off.

It was satisfying to feel the back of the car instantly rise up when the engine is started though. Made me feel good about the success of my rear suspension overhaul result.

[shogun]

Check once more the regulating valve and lever, when engine is running the lever should be at zero, = you could stick a screwdriver thru the hole on the lever and the hole on the housing. For example this one is not zero, as the 2 holes are not aligned.
$_1.JPG
The pics is from an E38 regulating valve, so just as info pic, same procedure however.

[Legoman]

This check is done with the car on the ground obviously?

[shogun]

Of course with the car on ground and possibly trunk loaded, see Bentley manual.
One way, if you do not have a pit, is to adjust the ride height in the rear is to back the car onto ramps. Loosen both 10mm nuts on the U-bolt on the stabilizer bar. Start the car...raise and lower the car to find the ride height you like by traversing the rod fore and aft..then tighten the U-bolt. Will take some trial an error. The good news is the LAD cannot tell if the car is on level ground...by design...so having the car on ramps will not affect the relationship of the body relative to the suspension...what you want during the adjustment process...the key being the distance from the lower lip of the road wheel to the top of the fender opening.
Bentley's has a table for LAD equipped cars as follows:
Wheels Rear ride height
15 in. 522 +/-3 mm (20.55 +/- 0.4 inches)
16 in. 529 +/-3 mm (20.93 +/- 0.1 inches)
17 in. 545 +/-3 mm (21.46 +/- 0.1 inches)

1 mm adjustment on the bar of the lever is/maybe about 1 inch of the ride height. So adjustment must be very careful is little steps.

Ride height is measured from the lower edge of the wheel arch to the bottom edge of the wheel rim (not the ground).

If you move the lever forward, in the driving direction, you also move the lever on the control valve forward and the result should be an increase in ride height, in reverse, moving the lever backwards, should result in a decrease of the ride height. First thing to do after a repair is to remove all the air from the system. You should raise the car with the wheels hanging free and the engine running, move the lever fully in the ‘UP’ direction and let it sit for 5 to 10 minutes. You should repeat this perhaps 2 to 4 days. Driving also aids in the removing of the air. The air collects at the top of the shock absorber which then in turn is removed by the previous procedure on the car lift. The only way I can tell, in my opinion, that all the air is gone is by repeating the above procedure. Then you can adjust the ride height. The lever on the control valve has in the center ( ‘0’) position, vertical, a small dead zone in the ride height control between raising and lowering the rear. You should check the center position carefully. One should slowly move the lever a little in the direction to raise the rear and listen carefully for the sound of flowing hydraulic oil. Small movements of the lever cause large changes. The trick is to adjust the ride height (with the prerequisite extra weight in the trunk) exactly at the point where you can hear the hydraulic fluid flow. You probably will need a few tries to get this right but you try to get the ride height correct at the onset of the hydraulic fluid noise. Now carefully tighten the lever without moving it relative to the stabilizer bar. Now check the ride height once more without the weight in the trunk, it should not have changed

[unity]

The lever will always be at zero, no way around it. Its the default position. There is no secondary mechanism to determine height.

[Legoman]

Got car backed up on ramps now. Just crawled under and found the alignment holes in the valve/lever assembly. All three holes line up perfectly. The first two might be one and the same thing (either side flange of a U-shaped metal arm bracket. The third hole goes straight through the edge of the cast aluminium valve body. Either way, all three holes line up perfectly. No problem threading a small screwdriver all the way through all three.

So with that check out of the way, is it looking like the accumulator bombs are the most likely source now of the leak down slumping of the rear suspension?

[shogun]

Maybe you make one more check for the regulating valve. In the evening when you park the car, open the Pentosin container and check the level; next morning check again, if the level is higher = the regulating valve let's Pentosin from the rear axle thru to the Pentosin container, so that would then be a leaking regulating valve.

[Legoman]

Hmmm, this is odd. I've just got back with the car and checked the PAS fluid level. Below the gauze strainer. Can't see any fluid at all without removing strainer. This is a big difference to the last time I looked when it was on the brink of overflowing the tank. So, I appear to have a fluid leak somewhere again though there's no evidence at all of that on the garage floor. Just guessing, but I'm going to start looking at the HP power steering line coming out of the compressor and running across the bottom of the radiator. Think it's this line: http://www.realoem.com/bmw/en/showpa...17#32411140932

I've had a suspected leak here before, but conclusion at the time was that it was okay, but maybe it's not.

[Legoman]

Well, have not managed to get to the bottom of this problem yet. Needs professional help, so car is booked for a weekend in at the mechanic soon. Have established conclusively there is no external fluid leak at all. There is however a pressure leak. The fluid must be running back into the Pentosin reservoir under the bonnet somehow. Pressure is not being retained for either brake pedal application or the rear shocks, hence why the car is sinking down on its haunches and the brake pedal being immediately hard from first press when checking Pentosin level.

I'm guessing either a leaky SLS regulator valve or failed rear suspension hydraulic accumulators (or combination of both). There simply aren't enough components in the system for it to be much else without any oil leaks. The rear shocks have been recently rebuilt last year. The brake booster has been replaced a while ago now, but it has been replaced. The accumulators were replaced 8 years ago. Only the SLS regulator valve is original and never been touched.

No errors reported on instrument cluster warning screen. Car behaves and drives perfectly normally albeit with a large rise in the rear on engine start. Obviously the rear shocks are not designed for that sort of duty cycle in movement though, so want to get this sorted before it results in oil leaks from the rear shocks again.

[shogun]

On my website are pics of a disassembled reglulating valve, and also there is a link on my website under links and lots of DIY to the site of Bryan, he has also good pics of all sinle parts of a regulating valve, there you can see that most of the rubber stuff are o-rings.
Translate this from a German language tech info:
Durch Erhoehen der Hinterachslast federt das Fahrzeug ein. Hierbei verdreht sich der Stabilisator und betaetigt ueber eine Stange den Drehschieber am Regelventil in Richtung heben.
Bei laufendem Motor kann nun das Oel zum Verteilerstueck und von dort ueber den Druckspeicher in die Federbeine und unter die Daempferkolben gelangen. Durch diesen Oeldruck wird die Karosserie angehoben und gleichzeitig verdreht sich der Drehschieber des Regelventils zurueck in die Nullage (Konstruktionslage). Mit Erreichen der Nullage schliesst das Regelventil und das von der Kolbenpumpe gefoerderte Oel fliesst durch die Ruecklaufleitung in den Oelbehaelter zurueck. Durch das Mindestdruckventil kann der Systemdruck hinter dem Regelventil nicht unter p = 30 bar fallen. Das Ueberdruckventil begrenzt den maximalen Druck und oeffnet bei p = 130 bar.
Die Abstimmung im Regelventil sorgt dafuer dass die waehrend der Fahrt auftretenden dynamischen Ein- und Ausfederbewegungen nicht ausgeregelt werden.
see drawing below: 1: Drehschieber, 2: Hebel, 3: Ruecklauf, 4: Vorlauf, 5: zum Verteiler, 6: Druckablassschraube, 7: Absteckbohrung

http://www.bimmerboard.com/members/jeffc/DSC03361sm.jpg
http://www.bimmerboard.com/forums/posts/511327
http://www.bimmerboard.com/forums/posts/538941

Control Valve
The rotary control valve located on the rear suspension has three positions:
• Raise
• Level
• Lower
The control lever is attached to the rear stabilizer bar to sense vehicle loading. When the vehicle is loaded (passenger or luggage) the suspension drops and the stabilizer bar twists. The control lever is moved in the "raise" direction.
With the engine running, oil flows from the pump to the bottom of the rear struts. The body of the car is lifted and the control lever returns to the level position. In the level position, the oil bypasses the valve and returns to the reservoir through the return line. A minimum pressure of 440 Psi (30bar) is maintained at all times. If service is required, a bleed off valve is installed on the control valve to drain the systems pressure.

Some more data:
LAD circulation/control/regulating valve
max. pressure 120 +/- 5 bar
min. pressure 30 +/- 3 bar

pressure reservoirs
at 20 degree Celsius 23 +/- 0.5 bar charging pressure

Pump LAD/circulating system
max pressure >120 bar
system pressure 50-60 bar
minimum pressure 30 +/- 3 bar

hydraulic switch / unit
switching point high pressure 110 +/- 12 bar
low pressure 30, + 4, - 2 bar

Pressure of a new LAD bomb gas filling is 23 bar.

Bentley table for LAD equipped cars as follows:
Wheels Rear ride height
15 inch 522 +/-3 mm (20.55 +/- 0.4 inches)
16 inch 529 +/-3 mm (20.93 +/- 0.1 inches)
17 inch 545 +/-3 mm (21.46 +/- 0.1 inches)

Ride height is measured from the lower edge of the wheel arch to the bottom edge of the wheel rim (not the ground).

[Legoman]

Thanks for that. All communicated to mechanic to hopefully limit their time trying to figure out what's going on.

Edit: Car in at mechanic's now. Can see the issue with sagging suspension but no real way of diagnosing the source of the problem. Suggested fix seems to be to just replace items in the system one by one until the problem is resolved. Not very cost effective way of doing things, but there we go.

I have decided to remove the regulator valve and have it rebuilt with all new perishables anyway seeing as how it is the only remaining mechanical item in between the shocks and the oil reservoir with O-rings and moving parts in it. The same shop that rebuilt my rear shocks is willing to tackle the rebuild for me. Another question I have since I'm getting that done: I retained an old brake booster that was leaking one time with the idea of having it rebuilt. I never got around to doing that at the time because the car needed to get back on the road and I didn't have the luxury of the time to rebuild the old brake booster, so a new one was fitted instead. Is it possible to rebuild old brake boosters? Can they be disassembled and rebuilt with new seals & perishables just like the SLS valve regulator & the rear shocks? If so, then I'll get this done at the same time and have a spare rebuilt brake booster on hand for the next time that lets go.

[Legoman]

Resurrecting this thread from the dead because my SLS rear suspension is sagging yet again. I've rebuilt the rear shock valve stems once and they're not leaking, so that repair at least appears to be good. The problem now I believe is the central regulator valve on the sway bar. I've rebuilt this too, twice with all new seals and o-rings and each time it only lasts about a year to 18 months, before it starts bypassing again. This time rather than repeat the exercise again, I need a better idea.

The regulator valve is NLA new for E32's I believe, so has anyone retrofit an E38 regulator valve to an E32 successfully before? I have no idea what's wrong with the rebuilt units I'm getting repaired but it seems they've been designed somehow to be irrepairable. It looks like the only long term solution is replacement with brand new. Any advice along these lines would be greatly appreciated.

[shogun]

Yes, some people have done it, you can use the regulator valve from the E38, BUT the arm/lever must be taken from the old E32 valve. On the German 7 forum we discuss that since 2016, super long thread, 160 posts, take your time and go thru it, with pics
https://www.7-forum.com/forum/showth...regulierventil
In post 138 I posted pics of a new E38 regulating valve 37121090628 and an old one from my parts bin to compare.
In post 155 I posted more pics how to assemble the lever, more in 157

[Legoman]

Yes, some people have done it, you can use the regulator valve from the E38, BUT the arm/lever must be taken from the old E32 valve. On the German 7 forum we discuss that since 2016, super long thread, 160 posts, take your time and go thru it, with pics
https://www.7-forum.com/forum/showth...regulierventil
In post 138 I posted pics of a new E38 regulating valve 37121090628 and an old one from my parts bin to compare.
In post 155 I posted more pics how to assemble the lever, more in 157

Erich can you please e-mail me directly the photos in posts 133 + 155. I can't access them without being logged in as a member of that forum and as I don't speak German I can't fight with a foreign language website to figure out how to register for it just to see six photos.

Thanks mate

[Legoman]

Yes, some people have done it, you can use the regulator valve from the E38

This seems weird. ECS are claiming in their description for it that it's a pneumatic valve rather than hydraulic on the E38? Surely a mistake? I doubt an air valve is going to work very long in a hydraulic system.

[shogun]

ECS desription of pneumatic valve for the E38 LAD is wrong. But on their pic you can see the E38 LAD valve and the difference to the E32 LAD valve, on the E32 valve the lever is straight, on the E38 the lever is curved. Pics sent to you, you can upload them here in the thread so the others can also see it.

[Legoman]

Pics sent to you, you can upload them here in the thread so the others can also see it.

RegV2_1200.jpg RegV4_1200.jpg RegV5_1200.jpg RegV7_1200.jpg RegVE38_1200.jpg

New problem now. Ordered and received the new E38 regulator valve. Car is up on hoist and the existing E32 regulator valve is bone dry and obviously not leaking, but both rear shocks are. Not leaking it appears from their valves in the base (which have been repaired before) but this time from further up. The shock bodies are all wet and the springs/perches are all wet with hydraulic oil.

Not a problem this time with the regulator valve, but it seems the shocks themselves. Is there are procedure for rebuilding the shock bodies and shaft seals top/bottom this time?

Cheers

[shogun]

forum software problem, I asked already the admin to fix it, try a few days later https://www.bimmerforums.com/forum/s...9#post30420289

[Legoman]

Final sixth picture I couldn't upload to the previous post (5 image limit)

Attachment 667617

[shogun]

The hole at the bottom of the LAD shocks is the bleeding hole. If further up it might be the top seal or it is normal, here is some info http://bmwe32.masscom.net/gavin/LAD_strut_rebuild.htm
if your shop can repair a regulating valve, for sure they can repair the LAD shocks, mostly o-rings and on the top is a seal with o-ring. The top seal usually get's damaged when the accumulators are dead and no more gas inside for a long time, then the shocks get hard hits without dampening. In case there is only some Pentosin "mist" outside of the LAD shocks, that is normal according to BMW SI.
Niveaulift Schwitzöl: An den hinteren Federbeinen der Niveauregulierung ist generell ein leichter Oelaustritt ueber die Kolbenstangenfuehrung vorhanden. Die Kolbenstange schleppt einen duennen Oelfilm mit, der sich ausserhalb der Dichtungs- und Fuehrungseinheit sammelt. Diese Oelleckage ist prinzipbedingt durch den hohen Systemdruck gegeben und ist im Gegensatz zu herkoemmlichen Federbeinen, die unter keinem oder geringem Systemdruck stehen, normal. Ausserdem kann beim Anheben des Fahrzeuges mit haengenden Raedern durch Schraegstellung der Federbeine ein momentanes Ueberlaufen des angesammelten Oeles beobachtet warden. Auch dies ist normal. Das uebergelaufene Oel ist vor dem Ablassen des Fahrzeuges unbedingt abzuwischen, um keinen wirklichen Oelverlust vorzutaeuschen! Oelstand im Ausgleichsbehaelter pruefen, ggf. nachfuellen. Federbeine fuer Niveauregulierung mit nach oben ausfahrenden Kolbenstangen duerfen bis maximal ueber die halbe Daempferlaenge am Aussenrohr oelfeucht sein - sie duerfen "schwitzen".

google translate: oil mist LAD: There is generally a slight oil leak on the rear suspension struts of the level control via the piston rod guide. The piston rod carries along a thin oil film that collects outside the sealing and guide unit. This oil leakage is inherent in the high system pressure and is normal in contrast to conventional struts, which are under no or low system pressure. In addition, a momentary overflow of the accumulated oil can be observed when lifting the vehicle with hanging wheels by tilting the struts. This is also normal. The overflowed oil must be wiped off before draining the vehicle in order not to "fake" a real loss of oil! Check the oil level in the expansion tank, top up if necessary. Suspension struts for level control with piston rods extending upwards may be dampened with oil up to a maximum of half the length of the damper on the outer tube - they may "sweat".

rv8flyboy posted on 2016-06-10 - Before u hit yourself up as a bad seal installer...
I been fighting leaking seals for a while myself, here is some food for thought.The shocks are not supposed to have fluid on top of the piston, if fluid is leaking at the top of the shock, you have fluid leaking past the piston, eventually the space fills up and is squeezed past the top shock rod seal whenever the piston needs to move up. Some is also blown back down past the piston seal when external forces, such as the springs, lift the rear up. This is due to the single acting design of the piston cup.For example, when u get out of the car, the back end wants to raise up, the trapped fluid is now compressed against the rod seal. So, if the piston is not fixed the leak will come back. How long you may ask, well that depends on the amount of leakage, for some it may be weeks, for others maybe years. Another thought... how are your accumulators, found mine shot, the back end very hard to push down, if at all, by hand. If you drive around with fluid logged accumulators every time you hit a bump or dip, the hydraulics will get a tremendous pressure shock. The fluid cannot go back quick enough through the ride height regulator valve. The compressed hydraulic fluid has to go somewhere so the rubber seals become the only place where there is compresibility, ergo, your seals are forced to deform beyond their capabilities and eventually will blow out. you can change seals till your blue in the face, if you don't address either the leak past the piston in the shock, or the accumulators, your leaks are bound to come back.
I did an experiment with a shock that leaked from the top and one that did not. I swapped piston and rod between them, left top seal in place, and sure enough after about a week or so, the formerly good top seal developed a leak, the shock with the top leak quit leaking (so far) from the top. on the one that did not leak from the top anymore, I blew the bottom seal, the one inside the 32 mm nut, a little while later, which necessitated a tow home. This is how I found out that every accumulator I had acquired over the years has empty. Just stick a small dowel through the center hole, if it goes in far enough to reach the far end, your bladder is shot. And if both your bladders are shot, the seals in the shocks probably wont be far behind for the reasons stated above. http://www.bimmerboard.com/forums/posts/1260639