525i Touring self levelling.

[ss2115]

I had the right-hand rear wheel and inner fender off over the weekend trying to find the source of a petrol smell when the tank is full (only).

While looking around, I noticed the sphere with ridgid steel line to it and larger flex line to the base of the shock strut.
Mine is wet with oil - although not dripping.
I put a spanner to the small steel line but it was already quite tight.

Where is the oil supply for this self-levelling system?
I'm not aware of an oil reseviour under the bonnet.

Is there a test procedure for this self-levelling system?

Is there a service schedule and service procedure for this self-leveling system?

How does the suspension check its height? - ie: is there a height switch somewhere. Perhaps on the sway bar?

Any advice on checking, servicing and common problem repairs would be much appreciated.

best regards,

[MicahO]

The self-levelling system draws it's hydraulic fluid from the power steering pump,which is why you need the CHF11 for steering fluid on most tourings. there is a lever that rides on the sway bar (iirc), attached to a valve, which allows some flow and pressure increase as the rear-end squats.

Bavarian has Self-Level Delete kits, their instruction pages have a reasonable diagram of the various components involved, minus the shocks.

http://www.bavauto.com/Assets/inst_pages/ins254.pdf

It's a decent system, though the replacement or even rebuilding the shocks can be very expensive, hence the reason for a lot of people to swap the system out and move to standard springs/shocks when it ages.

[shogun]

The sphere is completely made of metal outside, and here I have especially for you
cut a sphere and made some video to explain it.
http://twrite.org/shogunnew/upgrades&fun/cutestuff.html

The oil is Pentosin, older cars have Pentosin CHF 7.1 and the rest has Pentosin CHF 11S.
And the oil in in the power steering reservoir. http://www.bimmerboard.com/forums/posts/493140/
The power steering pump is a dual vane pump, one part for the power steering and the other part for the LAD.
The regulating valve is located on the rear axle, the detailked pics I have shown here http://www.7-forum.com/forum/24/komp...age-84467.html
you might need to register on the German 7-forum first to enlarge the pics.

System drawing http://s71.photobucket.com/albums/i1...mSchematic.jpg

Hydropneumatic Rear Leveling System
This module pertains to the hydropneumatic rear suspension system with the engine driven piston pump. The earlier system using the electro-hydraulic pump will not be discussed.
The self-leveling suspension system is designed to maintain vehicle ride height under loaded conditions.
The system is fully hydraulic, utilizing a tandem oil pump to supply pressure to both the suspension system and power steering system.
The system is installed on:
• E32 - 735 iL, 740iL and 750iL
• E34 - Touring 525i and 530i
• E38 - 740 iL and 750iL

System Components
The system consists of the following components:
• Tandem Hydraulic Pump
• Oil Reservoir
• Pressure Reservoir (2)
• Control Valve with Regulating Linkage
• Camber Warning Switch (E32 and E34)
• Rear Shock with LAD Module
• Expansion Hose, Pressure Lines and Distribution block.

Tandem Pump
The tandem pump consists of a vane pump for power steering and a radial pump for selfleveling suspension. Both pumps are driven by the same shaft and have separate oil feeds for each system.
The radial pump has the capacity to pump 102 liters of oil per minute. The maximum pressure is limited to 1900 Psi (130bar) by the pressure regulator located on the control valve.

Oil Reservoir
The single reservoir stores fluid for both the self-leveling and power steering systems.
Incorporated in the reservoir, is a reed type level warning switch. If the fluid level drops and the contact closes, a signal is sent to the check control module and a warning will be displayed
in the instrument cluster matrix display.
The hydraulic fluid required for the self-leveling suspension system varies between models and installed equipment. The following fluid is used:
• Pentosin CHF 7.1
• Pentosin CHF 11S
• Power Steering Fluid (BMW)
This type of fluid is used because of its low viscosity and low noise characteristics. It cannot be mixed with other fluid
types.
The self-leveling system fluid type is always marked on the top of the hydraulic reservoir. Always use the correct fluid never mix with another fluid.
When filling the system, be aware of the status of the level control system. If the vehicle is loaded, the level will appear to
be low. Do not fill the system unless it is in the resting state. Otherwise, an overflow situation could result.

Pressure Reservoirs
The oil pressure reservoirs (2) on each strut incorporate a membrane and are nitrogen gas filled. They are designed to absorb the oil which is expelled from the struts during downward movement, the gas in the reservoirs is compressed and pushes the oil back into the
struts during upward movement.

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.

LAD Module

The load dependent module is a control valve that regulates the flow of oil between the strut and the pressure reservoir.
The control piston in the (LAD) moves in relation to the pressure applied from the pump.
This movement will regulate the tension on the inner spring of the module. With only a low pressure applied, a small amount of tension
will be applied to the spring. Little flow resistance will be developed between the strut and pressure reservoir. The damping force is soft.

With a high pressure applied to the control piston, the flow resistance is high and the damping force will be stiff.

Camber Warning Switch (E32 AND E34 Touring)
The self-leveling suspension systems used in the E32 and the E34 Touring are equipped with a camber warning switch. The switch is mounted on the right rear axle support and connected through a rod to the semi-trailing arm.
The function of the switch is to warn the driver of an overload condition or an unsafe driving situation.
If the switch detects a rear wheel camber of -3.5 deg. A signal is sent to the check control module and displayed on the dash.
A time delay of 8 minutes is incorporated to prevent the warning from being displayed while driving through turns.
The E38 does not use the camber warning switch due to the design of the rear suspension.

Ride Height Measurement
When checking vehicle ride height with EHC, measure from the lower edge of the wheel opening to the center of the wheel hub.

More with drawings on various BMW models here, in total 53 pages
ftp://bmw-wiki.org/PDFs/selflevel.pd...=selflevel.pdf


and then see the rear axle I have disassembled
http://www.bimmerboard.com/forums/posts/272552/
you can see the alarm switch on the right

If it leaks, then you have to find a hydraulic shop which recrimps the new hoses, or buy new ones.
Here the not very professional way of a hydraulic shop
http://www.bimmerboard.com/forums/posts/269769/
A good hydraulic shop will cut the crimped part off and will use a new hose and crimp the sleeves on again
Here is a cut off sleeve and the old hose from my parts which we remade
http://img50.imageshack.us/img50/765...lauch136mn.jpg

what else you can buy instead of Pentosin from your VW dealer
http://www.bimmerboard.com/forums/posts/654628/


The ride height is adjusted to a predefined height (distance from the edge of the rim to the edge of the wheel well) with the pre-define weight in the trunk. Both values can be found in the TIS. Here is a trick from my own experience that should make the job easier. You should loosen the lever on the stabilizer so you can change the adjustment. 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, It took 4 days before I felt the car was stable again in cornering and driving, and I did not have sudden changes in characteristics. After a few days 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 Note: Theory and real world are two different entities and there is no sure method to remove the air. I removed the air 5 times on the same day and re-adjusted the ride height , then I would find the car the next morning sunk uneven again. the abnormal drive characteristics disappeared at the same time the pentosin level stabilized. Note: The car stood lower in the right, but the left side would also sink over night, as measured with a ruler. When the car started the rear would pump back up, but the pentosin level would be permanently a little lower unrelated to the control valve and the new bombs. Mainly the right side maintained a lot of air in the shock absorber. I have a special test corner and the car would go soft in the rear, something that never happened with the olf shock absorber. But luckily now the right shock is okay.

[shogun]

in case you want to eliminate the LAD warning complete, here how to modify the CCM
http://www.bimmerboard.com/forums/posts/667920

[ss2115]

What a fantastic amount of information from everyone - thank you.
If I can't work it all out from this, then I should hang up my spanners for good!

[ss2115]

Actually, I do have something to ask.

This system is very much the same as the Citroen suspension system.
What you call "bomb", they call a "sphere", but they are the same function and construction.
In the Citroen spheres, they occasionally require re-pressurising with the Nitrogen gas. Some of the older spheres are serviceable so you can replace the inside rubber membrane that seperates the gas and oil - later ones are throwaway & replace if they won't re-charge (which means the rubber membrane has ruptured).

What is the service life of the BMW units?
Can they be re-charged / or / do they lose pressure over time at all?
Is there an on-car test for them to determine their serviceability?

Would a valid test be as follows -
Run the engine and manually operate the height control switch and observe the suspension raise & lower.
Then switch off the engine and after a minute or so operate the height switch manually again. If the spheres (bombs) are in good condition, the suspension should raise at least one or two times evenly before the residual pressure is extinguished.
If nothing happens, then the spheres are duds and the suspension was operating on the pump pressure only.

This would only work if there is not some device that releases residual pressure once the engine is turned off. But if this is so, then the back of the car should sink quite quickly if its loaded and the engine is stopped.

Appreciate comments and more testing info.
best regards,

[shogun]

Hi Shaughan
I know that you have the Citroen. I also have one, one of the last produced 2CV Charleston with only 1.200 km on the clock. Bought new and put into my shack.
But that is another story.

What is the service life of the BMW units?

20 years so far and still doing o.k. That means about 160.000 kms driven on excellent roads.

Can they be re-charged / or / do they lose pressure over time at all?

cannot be recharged, I checked that because I know the Citroen system. The one we cut off has on one side a spot weld, apparently they add there the gas and then close it

Is there an on-car test for them to determine their serviceability?

yes, but quite complicated, see the pics in above link from the German 7-forum. http://www.7-forum.com/forum/24/komp...tml#post952281
You need some special equipment. We have discussed that in our group of DIYers, the best way to test a bomb is to push a screwdriver in (no worry there is the plastic piece) the hole where the connection for the hose goes. If you can push it in, it lost gas already = the inner sphere is leaking. If you cannot push the screwdriver in, the bomb is o.k.
The pressure inside is 23 Bar! Probbably you cannot push that in, I found that out in January 2009 in this thread
http://www.7-forum.com/forum/5/nivea...rt-105597.html

Would a valid test be as follows -
Run the engine and manually operate the height control switch and observe the suspension raise & lower.
Then switch off the engine and after a minute or so operate the height switch manually again. If the spheres (bombs) are in good condition, the suspension should raise at least one or two times evenly before the residual pressure is extinguished.
If nothing happens, then the spheres are duds and the suspension was operating on the pump pressure only.

This would only work if there is not some device that releases residual pressure once the engine is turned off. But if this is so, then the back of the car should sink quite quickly if its loaded and the engine is stopped.

such a test is not necessary. If the gas is partly or all gone, all the space inside the bomb is filled with Pentosin, and the outer shell of the bomb is steel, nothing can escape = instead of gas is now Pentosin to fill the space. To find out a dead bomb in installed condition: the rear is dead hard, no suspension at all. Because the bombs are actually the dampers for the shocks.
If you run the engine that the rear is on correct level, and then the next morning it is down on the rear, there can be only 2 reasons:

1. the regulating valve is not set at zero point (or leaking) and lets Pentosin flow overnight from the rear to the engine room back. Easy check is to have a look into the Pentosin container when you stop the engine and another look next day when/before you start the engine. If more Pentosin, it comes from the rear thru the return line = regulating valve problem.
2. might be air in the system, but basically it bleeds itself in most of the system, but when there is air in the shocks, you must raise the rear that the shocks are extended, then the little bleeding valve at the bottom of the shock is bleeding. See pic in the German link.

[ss2115]

Hi Shaughan
I know that you have the Citroen. I also have one, one of the last produced 2CV Charleston with only 1.200 km on the clock. Bought new and put into my shack.
But that is another story.


20 years so far and still doing o.k. That means about 160.000 kms driven on excellent roads.

cannot be recharged, I checked that because I know the Citroen system. The one we cut off has on one side a spot weld, apparently they add there the gas and then close it


yes, but quite complicated, see the pics in above link from the German 7-forum. http://www.7-forum.com/forum/24/komp...tml#post952281
You need some special equipment. We have discussed that in our group of DIYers, the best way to test a bomb is to push a screwdriver in (no worry there is the plastic piece) the hole where the connection for the hose goes. If you can push it in, it lost gas already = the inner sphere is leaking. If you cannot push the screwdriver in, the bomb is o.k.
The pressure inside is 23 Bar! Probbably you cannot push that in, I found that out in January 2009 in this thread
http://www.7-forum.com/forum/5/nivea...rt-105597.html



such a test is not necessary. If the gas is partly or all gone, all the space inside the bomb is filled with Pentosin, and the outer shell of the bomb is steel, nothing can escape = instead of gas is now Pentosin to fill the space. To find out a dead bomb in installed condition: the rear is dead hard, no suspension at all. Because the bombs are actually the dampers for the shocks.
If you run the engine that the rear is on correct level, and then the next morning it is down on the rear, there can be only 2 reasons:

1. the regulating valve is not set at zero point (or leaking) and lets Pentosin flow overnight from the rear to the engine room back. Easy check is to have a look into the Pentosin container when you stop the engine and another look next day when/before you start the engine. If more Pentosin, it comes from the rear thru the return line = regulating valve problem.
2. might be air in the system, but basically it bleeds itself in most of the system, but when there is air in the shocks, you must raise the rear that the shocks are extended, then the little bleeding valve at the bottom of the shock is bleeding. See pic in the German link.

Thanks Shogun.
I understand it a lot better now.

I thought the bomb was an accumulator for the oil pressure to reduce the work of the pump, but you are saying that they are actually the suspension - just like the Citroen.

So in this case, I don't think I have any problem then because my suspension stays the same height if parked overnight, the car is level whenever I see it front to back, and it doesn't sag on one side.
Also the ride is nice - sometimes too soft with just me in the car on my own.

I just need to check why it is damp around the bomb.
I have no warning about low oil in the steering system, but I will check the level to make sure.

Yes - I have a 1974 Citroen DS23 Safari wagon with BVH.
There are few Safari's with BVH, so mine is a little bit rare, but not extraordinary. It also has many Pallas features, but is not a Pallas. It was a special order from the factory.

Thanks again.

[shogun]

Usually the 'damp' or 'sweat' starts from the crimped hoses, that is the first sign that you need to do something, especially where the hose is crimped with the crimping shells. As you are not in a hurry, look out for a hydraulic ship or a repair shop for agri equipment/road construction machinery/ship repair service, they can crimp you new pressure hoses on the original steel connections.
Much cheaper than buying new ones from the dealer, and much cheaper if you live in Australia.
The hoses and crimps sleeves come originally from Cohline in Germany, which is a subsidiary of Continental now.
I am trying to get a small hydraulic press for high pressure hoses/sleeves and then do it for our club members. Here in japan the hydraulic shops refuse to handle such stuff for cars, similar in other countries. So tell them it of for off road or for you tractor on the farm.
If you find a source for the sleeves and hoses in AUS, as well as a small hand crimping press (the the cheap stuff for aircon hoses), let me know, I might also buy then there.

Another problem for leaks are too much tightened banjo bolts for example on the power steering pump hoses, if tightened too much, they break around the hole/thread inside the threaded area, so you cannot see a broken banjo bolt till you remove it. Do not tighten too much, and have some spare banjo bolts and these copper washers as spare.

[ss2115]

Usually the 'damp' or 'sweat' starts from the crimped hoses, that is the first sign that you need to do something, especially where the hose is crimped with the crimping shells. As you are not in a hurry, look out for a hydraulic ship or a repair shop for agri equipment/road construction machinery/ship repair service, they can crimp you new pressure hoses on the original steel connections.
Much cheaper than buying new ones from the dealer, and much cheaper if you live in Australia.
The hoses and crimps sleeves come originally from Cohline in Germany, which is a subsidiary of Continental now.
I am trying to get a small hydraulic press for high pressure hoses/sleeves and then do it for our club members. Here in japan the hydraulic shops refuse to handle such stuff for cars, similar in other countries. So tell them it of for off road or for you tractor on the farm.
If you find a source for the sleeves and hoses in AUS, as well as a small hand crimping press (the the cheap stuff for aircon hoses), let me know, I might also buy then there.

Another problem for leaks are too much tightened banjo bolts for example on the power steering pump hoses, if tightened too much, they break around the hole/thread inside the threaded area, so you cannot see a broken banjo bolt till you remove it. Do not tighten too much, and have some spare banjo bolts and these copper washers as spare.

Thanks again.
There are a couple of hydraulic franchises in Australia - Enzed being very popular. They are all quite happy to make lines etc for cars and Enzed will make up brake lines in steel or flex, braided/non-braided etc without any fuss.
They usually carry just about every possible type of hose and also a huge range of fittings in brass, stainless etc.
Usually they make it up for you while you wait. They also have on-site trucks etc for mobile repairs and will come to your house and make up lines for your car with you as long as your willing to pay for their time.

Can you advise the correct procedure for disconnecting the lines to the wheel for replacement without being sprayed by 23bar pressured oil?
I guess it would be something like jack the back and leave the wheels hanging. Leave for a few hours or days to remove residual pressure and then disconnect and plug.