LAD problems

[cmk]

The back-end is riding like there are no shocks.
I've read all of (shoguns) links and still can't decide if the accumulators are gone.

While the engine is running and i push down on a (rear) corner:
- it moves down
- it could just be springs being loaded
- i can't tell if shocks involved
- resisitance feels same as front corners
- front corners are EDC ... and may be bad as well (sigh)
- while holding it down with my weight (200lbs) i don't feel it rise
- when i release it goes back to previous position

So, to me, i would think, if it was just the accumulators, i would still feel the back end rise when i load it, as the LAD kicked in.

If so, then how do i determine if it is the pump or the regulator valve that is gone ?

[shogun]

O.k., let's try this.
When you park the car in the evening (best is always same place to measure) measure the ride height from edge of fender to middle of the BMW emblem in the center of the wheel. Try to have always about the same fuel inside.
Next morning check again.
If it goes down, it cannot be the pump, but the regulating valve.
Also, after you parked the car in the evening, open the lid of the Pentosin reservoir and check the level. Open it again in the morning. Probably it will be higher = the regulating valve lets Pentosin flow back from the system.
It is not that difficult to eliminate one after the other possibilities to pin down the real one.
Others: load the trunk while engine is off: then start engine, rear should go up again to normal level. Again measure ride height in all steps.
Usually the bladders of the bombs are gone when you have the feeling that the rear sus is stone hard. because the 'cushion' from the bladders is no longer there.
Let me know what you find out.
I have checked so many E32, and I have presently 5 750 E32 in my 'scrapyard", but only one of the 5 has a prob with the LAD.
And that was an exploded 'bladder' inside of the bomb. My daily driver is from 1988, not any drop of Pentosin comes out from the shocks. I only had to replace the hoses in the engine room.

[cmk]

Ok, i'll measure the heights and today/tomorrow.

The ride is stone hard, but that could be either the bladders are gone, or there is no pressure and the 'lifts' are bottomed out (i.e. no movement for bladder to absorb).

Thanks.

[shogun]

Check the Bentley for the normal ride height. It is today online as you see from another posting, if you do not have one. Also depends in the wheel size. They indicate for the 32 for 3 different wheel sizes.
If you say stone hard, my bet is the bladders.

[Bill R.]

rear strut mount will flex quite a bit when you push down on the rear of the car giving you a misleading feeling and also the strut will allow some fluid to go back into the pressure accumulators even when they are bad, its just that there isn't enough pressure in the bladder to really absorb and supply fluid to the strut.. Also since your car has edc front and rear then if the edc has a fault in it then it automatically defaults to the middle shock firmness setting and if there's a fault in that system then with the solenoids not energized it will default to the firmest shock setting which won't help the ride to be any softer either..






The back-end is riding like there are no shocks.
I've read all of (shoguns) links and still can't decide if the accumulators are gone.

While the engine is running and i push down on a (rear) corner:
- it moves down
- it could just be springs being loaded
- i can't tell if shocks involved
- resisitance feels same as front corners
- front corners are EDC ... and may be bad as well (sigh)
- while holding it down with my weight (200lbs) i don't feel it rise
- when i release it goes back to previous position

So, to me, i would think, if it was just the accumulators, i would still feel the back end rise when i load it, as the LAD kicked in.

If so, then how do i determine if it is the pump or the regulator valve that is gone ?

[cmk]

I measured when i went out (it was sitting all night), again after letting the car idle for a couple of minutes, and then again after driving around for a while.

All the measurements for a given wheel stayed within 1/4".
I also measured the PS fluid level, and it didn't move at all.

Measuring from center of wheel arc to center of hub:
- front left/right 14" / 14 1/8"
- rear left/right 13" / 13 3/8" (back right fender has had body work, i assume that's most of the 3/8" difference)

Bently's has a 15" wheel from center of wheel arc to bottom of wheel rim:
- front 22 1/8" ( -7 1/2" to get to center of hub = 14 5/8")
- rear 20 1/4" ( -7 1/2" to get to center of hub = 12 3/4")

So it seems my fronts are riding 1/2" low, and the rears maybe 1/4" - 1/2" high.

[cmk]

I had thought the struts in the back were more or less 'lifts'.
That the actual 'shocking' effect was handled by the accumulators.

How does EDC on the rear alter that ?
Do the struts now perform some of the shocking (via EDC), or was i incorrect in my original assumption ?

[Bill R.]

the lifting cylinder, but they still have an orifice to control the rate at which the fluid flows through the strut just like a shock and they still have the edc portion of it which is a couple of larger orifices controlled by a solenoidhttp://www.bimmer.info/%7Ebill/Selfleveling.jpg






I had thought the struts in the back were more or less 'lifts'.
That the actual 'shocking' effect was handled by the accumulators.

How does EDC on the rear alter that ?
Do the struts now perform some of the shocking (via EDC), or was i incorrect in my original assumption ?

[cmk]

Ahhh.
Thanks, a picture is worth a thousand words.

[High Compression II]

This is just a pure guess, as Im not familiar with the BMW set-up. Looking at the diagrams its a little like the Citroen BX/Xantia set up which I do know. The part you call the Accumulator, in the Citroen is called the Sphere, and acts as the suspension spring/shock absorber combined. The fluid transferring the pressure/motion to the high pressure gas above the diaphragm in the sphere. Over time, the Nitrogen gas will leak out, a common problem with Citroens with hard suspensions. My guess is the same has happened here in the BMW set-up The nitrogen gas in the Citroens is at a Very high pressure, commonly around 30-50 Bar, and this is why it leaks out over time The gas permeates through the membrane/diaphragm and through the metal walls of the sphere.................
This set up of Hydro-Pneumatic Suspension was first used on the Classic Citroen DS of the late '50's and 60's, where they had huge problems of gas leakage untill better diaphragm materials were made available such as neoprene and others.........
Variable-rate shock-absorbance is effected by the valving of the fluid into and out of the sphere, just as described above in the Citroen as well.....

Figure on a life of around three years for a Sphere/Accumulator with average use, and say two years for hard use. Some Citroen fanatics change these things every year, for that perfect ride Citroens are renound for........

For a better description of the Citroen set-up, check out this link--
http://www.tramontana.co.hu/citroen/suspens/suspens.html

[Bill R.]

charging pressure of 23 bars on the spheres or bombs as they are commonly called.... and they typically last about 10 years on these... I start to see a number of them when they get close to 100k miles or 10 years or so time..









This is just a pure guess, as Im not familiar with the BMW set-up. Looking at the diagrams its a little like the Citroen BX/Xantia set up which I do know. The part you call the Accumulator, in the Citroen is called the Sphere, and acts as the suspension spring/shock absorber combined. The fluid transferring the pressure/motion to the high pressure gas above the diaphragm in the sphere. Over time, the Nitrogen gas will leak out, a common problem with Citroens with hard suspensions. My guess is the same has happened here in the BMW set-up The nitrogen gas in the Citroens is at a Very high pressure, commonly around 30-50 Bar, and this is why it leaks out over time The gas permeates through the membrane/diaphragm and through the metal walls of the sphere.................
This set up of Hydro-Pneumatic Suspension was first used on the Classic Citroen DS of the late '50's and 60's, where they had huge problems of gas leakage untill better diaphragm materials were made available such as neoprene and others.........
Variable-rate shock-absorbance is effected by the valving of the fluid into and out of the sphere, just as described above in the Citroen as well.....

Figure on a life of around three years for a Sphere/Accumulator with average use, and say two years for hard use. Some Citroen fanatics change these things every year, for that perfect ride Citroens are renound for........

For a better description of the Citroen set-up, check out this link--
http://www.tramontana.co.hu/citroen/suspens/suspens.html

[shogun]

I have not changed the bombs and shocks on my E32 750iL from 11/1988. No leaks, bombs are fine. The only parts I changed in the system were hoses/pipes in the engine room, going down from the Pentosin reservoir tank. That was last year.
Car has now 126K km.
Then I have a 750iL from 10/1988 which I just part and inspect all the parts.
180K km, no leaks on bombs and shocks, some small leaks in engine room hoses.

Then I have a 750iL Highline from 03/1990, 130 K km. no probs on bombs, shocks. car is parked at the monent due to some project work. I check evey week the rear level. It goes down by 5-10 mm only. Then I let the engine run for maintenance or similar for a short time. Rear goes up to normal, after one week again 5-10 mm. The regulating valve might be a bit damaged/leaking back to the front (not outside). In the engine room again leaks from hoses from reservoir tank to other parts in the engine room. These are the parts which are to be replaced after 10 or more years, depending on mileage and road conditions and driving style.
Then I have another 750iL Highline from 1991. That is the only one which has a damaged bomb on the drivers side. 190 k KM.
In general, I believe that system is quite reliable. 15-18 years old and still working, not too bad.
Most of the leaks come from the hoses/pipes in the engine room. And that is quite time consuming to repair it in the tight engine room of the 750.

@BillR: are the regulating valves underneath the car serviceable?
Either I repair the one on my blue Highline or I use the one from the parts 750iL. But as you know, I always want to try at least to repair it to prove that something is repairable.
Here a direct link from my website about the EDC and LAD. Item 1.4.4 shows the regulating valve cross section.
http://tridem.han-solo.net/auto/erich/edc/edc.htm

[Bill R.]

regulating valve on one so I don't know if its repairable or not..




I have not changed the bombs and shocks on my E32 750iL from 11/1988. No leaks, bombs are fine. The only parts I changed in the system were hoses/pipes in the engine room, going down from the Pentosin reservoir tank. That was last year.
Car has now 126K km.
Then I have a 750iL from 10/1988 which I just part and inspect all the parts.
180K km, no leaks on bombs and shocks, some small leaks in engine room hoses.

Then I have a 750iL Highline from 03/1990, 130 K km. no probs on bombs, shocks. car is parked at the monent due to some project work. I check evey week the rear level. It goes down by 5-10 mm only. Then I let the engine run for maintenance or similar for a short time. Rear goes up to normal, after one week again 5-10 mm. The regulating valve might be a bit damaged/leaking back to the front (not outside). In the engine room again leaks from hoses from reservoir tank to other parts in the engine room. These are the parts which are to be replaced after 10 or more years, depending on mileage and road conditions and driving style.
Then I have another 750iL Highline from 1991. That is the only one which has a damaged bomb on the drivers side. 190 k KM.
In general, I believe that system is quite reliable. 15-18 years old and still working, not too bad.
Most of the leaks come from the hoses/pipes in the engine room. And that is quite time consuming to repair it in the tight engine room of the 750.

@BillR: are the regulating valves underneath the car serviceable?
Either I repair the one on my blue Highline or I use the one from the parts 750iL. But as you know, I always want to try at least to repair it to prove that something is repairable.
Here a direct link from my website about the EDC and LAD. Item 1.4.4 shows the regulating valve cross section.
http://tridem.han-solo.net/auto/erich/edc/edc.htm

[motuman]

rear strut mount will flex quite a bit when you push down on the rear of the car giving you a misleading feeling and also the strut will allow some fluid to go back into the pressure accumulators even when they are bad, its just that there isn't enough pressure in the bladder to really absorb and supply fluid to the strut.. Also since your car has edc front and rear then if the edc has a fault in it then it automatically defaults to the middle shock firmness setting and if there's a fault in that system then with the solenoids not energized it will default to the firmest shock setting which won't help the ride to be any softer either..


If the EDC shocks are (failed) in the firm position all the time and the dash switch is still lit, but not casuing any difference in ride when switched, what should be checked? EDC controller? Is the any way to manually energize the solenoids on the shocks to see if they are working?

Thanks!