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Thread: Rock hard rear suspension

  1. #1
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    Rock hard rear suspension

    My 735iL rear suspension is rock hard. It bounces like mad. Everything I've read points to the accumulators, so I replaced those with brand new units and fully bled the system per the Bentley manual with CHF11S fluid. It made zero difference. What on earth could be causing this? I know my EDC3 system is not operational due to a broken pigtail on the acceleration sensor (fix in progress) but would that cause these symptoms?

  2. #2
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    If EDC fails it faults to "sport" mode I believe. So it may be firm, but should not be bouncy. Does the rear end look oddly low? Also keep in mind you may need some extended drive time. The hydraulic system is a dead end at the rear, meaning there is just one line going from the rear leveling block, to the accumulator, to the shocks. Its not a loop where fluid can cycle through. So if the fluid was really bad, it will take a bit for it to cycle back and forth from the system into the shocks. One way to speed this up is to get the rear end up on ramps then adjust the rear block heigh lever to lower the rear down and up several times. Also there is always a change the rear shock are shot. While robust, rebuilds have shown they do wear and internal parts do break.
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  3. #3
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    Ya I know the default for EDC is to "sport" but this is waaaayyyy beyond firm; it's downright punishing. There is literally zero compression in the rear suspension. I've street driven Pro3/SpecE30 cars to shows before and they had more compliant suspension that this haha. The front end feels exactly like a 7er should though.

    The PO used ATF in the system. I removed/drained as much as I possibly could while doing the accumulators (suctioned out the reservoir, removed lower PS hose from pump, and removed lines between accumulators and shocks), and when I refilled with CHF11S I used the bleed screw on the regulating valve to purge the lines until new, clear CHF ran out of it. Still, the valve is upstream of the shocks so I suppose ATF could still be in them if it didn't drain out via gravity while the lines were disconnected.

    Does the rear ride height affect the firmness? Right now I have it set to max height (we're doing the Gambler 500 in this car so ground clearance is important) but I wouldn't think ride height would affect it like this. I'll try the trick to raise/lower it a few times and see if I can get the new fluid to circulate fully.
    Last edited by DarinS; 05-31-2019 at 02:11 PM.

  4. #4
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    Yes, the rear height has a big impact on the ride. The 7 should have a slightly higher rear end than the front when looking at the rockers. Mine always rode a little rough but I left it. Before selling I adjust it up, 1/2" to an inch tops. Made a huge impact and I wished I had done it when I was using it as a daily years ago. I suppose like most shocks it has a "sweet spot". Its why off-roaders often installed absorbers that are appropriate for suspension lift increases.
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  5. #5
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    Tried changing the ride height (full low, middle, full high) and it has no impact on the stiffness. Which isn't really a surprise, ride height and stiffness aren't really affected by one another, i.e. EDC3 vs LAD.

  6. #6
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    If the accummulators are new and the ride height is adjusted to correct height, then I only can imagine that the EDCIII causes this, the technical description says when EDCIII is not working properly then it will go automatically into sports mode = hard.
    Once one of my wrenching buddies had a defective EDCIII control module and that caused a real stiff rear sus.
    Shogun tricks and tips for the E32 series are HERE!

  7. #7
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    I know the EDCIII system isn't currently active because the wiring pigtail going in to the acceleration sensor is broken (need to source one from a junkyard). However the front suspension is fairly soft and compliant, just like a 7er should be. It's only the rear that's rock hard. I would assume that rules out EDC as it acts on front/rear equally.

  8. #8
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    I wonder if the new accumulators were manufactured a long time ago. Is it possible the nitrogen has leaked out of them over the years?

  9. #9
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    That is one possibilty, have heard similar things on the German forum, old stock looses every year a certain percentage of the gas, ATE for example scraps the stock bombs after 5 years I heard.
    Did you check the bombs before installing them? Here Gert shows how to test, he stuck a long screwdriver inside http://www.bimmerboard.com/forums/posts/1261417/

    You can also test removing the EDCIII control module in the trunk and drive, it is in the black plastic container behind the spare wheel
    Shogun tricks and tips for the E32 series are HERE!

  10. #10
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    <edit>
    Last edited by unity; 05-31-2019 at 09:02 PM.
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  11. #11
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    Quote Originally Posted by m60power View Post
    I wonder if the new accumulators were manufactured a long time ago. Is it possible the nitrogen has leaked out of them over the years?
    Interesting idea, I hadn't thought of that. These were Febi units but I have no idea was the mfr date was. I'll look for a stamp on them.

    Quote Originally Posted by shogun View Post
    That is one possibilty, have heard similar things on the German forum, old stock looses every year a certain percentage of the gas, ATE for example scraps the stock bombs after 5 years I heard.
    Did you check the bombs before installing them? Here Gert shows how to test, he stuck a long screwdriver inside http://www.bimmerboard.com/forums/posts/1261417/

    You can also test removing the EDCIII control module in the trunk and drive, it is in the black plastic container behind the spare wheel
    I seem to remember my EDCIII module being under the rear seat next to the battery. Either way I know the system is not fully active because the acceleration sensor is not plugged in. But perhaps disconnecting the module will deactivate the system completely.
    Last edited by DarinS; 06-02-2019 at 10:29 AM.

  12. #12
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    I'd say that brake bomb could be shot. I had similar symptoms with brake pedal kicking back when braking on my 750i. All fixed when I changed brake bomb.

  13. #13
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    This car doesn't have a brake bomb, it's a standard vacuum booster. So the SLS and EDC systems are totally separate from the braking system.

  14. #14
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    From my reading of the EDC section in the Bentley manual, the EDC solenoid valves are power on/open. So if they're not receiving power, the valves close and restrict fluid flow which means firmer damping (hence why the system defaults to "sport" when there is a malfunction). However "sport" doesn't mean "welded solid", which is what I'm experiencing. However I am going to try running 12V to the solenoids and see if that makes any difference. Perhaps they're seized in some way and not allowing any fluid to flow. It is also possible that there is a blockage in the hydraulic lines between the shocks and the accumulators which is preventing any fluid flow during compression.

    Regarding the relationship between SLS/LAD and EDC, going back to my fluid mechanics and physics fundamentals tells me that there is little correlation between them. LAD operates off of pressure, 30-130bar as determined by the regulating valve. EDC works off of flow, and resistance to that flow (controlled by the solenoids) is what changes the damping firmness. Compliance (i.e. how stiff the ride is) is a function primarily of spring rate and accumulator N2 pressure, and secondly of EDC solenoid position. The ride height as determined by LAD pressure has little effect on damping or compliance, as pressure and flow in this system are only loosely correlated, and are controlled by separate systems, parts, and methods.

  15. #15
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    A follow-up on this: After letting the car sit for ~2 weeks, I drove it around and surprisingly there was *some* compliance in the rear suspension. It was still very firm, but at least it moved. Unfortunately after lifting the car do do some other work and then lowering it back down, it went right back to being solid again. Pressed for time and needing to get this solved in time for the OG Gambler 500, we ripped out the SLS shocks and replaced them with some non-SLS struts I gout of a junkyard 740i, which surprisingly has really health Bilstien HD shocks in them. Took 30 minutes and cost me $24, and the ride is sublime. We were blasting down washboard gravel roads at 50mph like it wasn't even there, while the poor guys in Jeeps were getting destroyed at 30mph. So to anyone who is curious, the E32 makes a great Gambler car!

    Also, if anyone needs accumulators, we've got two like-new accumulators with <50 mile son them that we no longer need.

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