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Thread: Am I wrong to insist on preserving (And rebuild) the SLS on my 1985 BMW 745i?

  1. #1
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    Am I wrong to insist on preserving (And rebuild) the SLS on my 1985 BMW 745i?

    Hi everyone.

    I have a near stock BMW e23 745i and have a very bouncy rear but acceptable overall. I am at a cross road

    1) Do what everyone else and switch to coil overs (CEIKA?)
    2) Do what some dared to do. airlift/airbag suspension (CEIKA?)

    or
    3) Attempt to rebuild it fully.

    Am I wrong to lean towards option 3? This could be my daily driver and not for spirited driving (I other other mean cars for that purpose)... so should I simply stick to rebuilding (ASSUMING IT'S DOABLE in the MD metro area) or go with options 1 or 2 above. Does any of those options match or beat the OEM handling (which some may find obsolete)...

    IMAG0844_2.jpg
    Last edited by abdoul; 05-27-2022 at 01:31 AM.

  2. #2
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    For a regular driver car, using the trunk, having the stock set up will work just fine. It was designed to allow trunk loading without upsetting the level of the car. I'm sure suspensions are better today but as a daily driver, is the improvement needed?

    Not knowing costs. keeping it original is not a bad idea.

  3. #3
    moroza's Avatar
    moroza is offline MORΩN ΛABIA BMW CCA Member
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    E34 Touring owner here, with much the same double-jointed sorta-Mac strut front and semi-trailing rear as your E23. I understand the E23 hydropneumatic rear uses an electrohydraulic pump instead of a mechanical one, but otherwise the system is the same as an E34 or E32. I've been singing the praises of factory SLS since I retrofit it into my 525iT that didn't come with it. Doing it completely stock may be difficult or overpriced, because of accumulators that are tricky to ship and hoses that are out of production. However, I've figured out aftermarket solutions to both and been enjoying mine in daily use for a couple of years now; see the link in my sig. I doubt your E23 will ever carry as many engines, hay bales, refrigerators, or other crap that my Bavarian Manure Wagon schleps on a regular basis, so payload capacity is probably not a priority for you, but what may be more important is what just about nobody mentions when discussing SLS: it significantly improves the ride over a conventional suspension. This is for three reasons as I see them: 1. softer spring rate, allowable because it no longer needs to be high enough to support maximum GVW, 2. steep spring rate progression, due to how the pressure accumulators behave, and 3. variable damping rate, due to the pressure-sensitive damping module in the struts. Rather than a single spring and damping rate chosen as a compromise for the rear suspension's operating envelope, SLS varies both rates as a function of ride height, in a way that's relatively easy to modify as well.

    Airbags may yet ride better (though SLS pressure accumulators basically are airbags); this is the first I hear of such an option. No conventional suspension can possibly match SLS' versatility and range of good performance.

  4. #4
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    Frankly my only rear passengers will be shopping bags 95% of the time.

    - - - Updated - - -

    I might remain the stubborn purist... and rebuild it somehow..... I learned a lot from your replies. Thank you!!
    Last edited by abdoul; 05-30-2022 at 04:34 AM.

  5. #5
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    Uh oh. Another urgent issue to address. Just noticed dry rotted shock towers... ��

    PXL_20220528_162616078.jpg

    PXL_20220528_162625077.jpg
    Last edited by abdoul; 05-30-2022 at 05:49 AM.

  6. #6
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    Thumbs up

    Those strut mounts will run you about $500 for a pair. You should replace that expansion tank too as it looks a bit long in the tooth. You also have some wonky vacuum action at your pump there.

    The OE SLS is pretty simple on these, accumulator wise look to 80s MBs. 201 Cosworth. 560SEL and SEC. 70s MBs also had them. One of the members here rebuilds the pumps, the electronics seem pretty solid...just fluid flows but makes no pressure due to oring shrinkage.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  7. #7
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    I lowered my E23 745i with Mtechnic OEM springs and ran E28 M5 Rear SLS Struts which were overall slightly shorter that the stock E23 ones, for years and was very happy with the overall, comfort + handling.

    You can cut the top of the strut open and replace seals, o-rings and sleave bearing, then reweld it back together. As Morozza said above, go outside the automotive market, and find a hydraulics shop that will work with you

    DSCN0111.JPGDSCN0109.JPGDSCN0107.JPGDSCN0115.JPGDSCN0113.JPG

  8. #8
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    close up of sleeve bushing


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  9. #9
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    Agreed, they are simply hydraulic rams. I had my high side lines for the rear rebuilt at a hydraulic hose shop, just like the hydroboost lines under the hood.

    The dampening is controlled by the accumulator. It is a very basic system, my only question would be that switch under it. I think Craig on here has his system 100% still and said it was simply a mercury trigger switch to turn the pump on.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  10. #10
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    Thank you. Will look into it.

    - - - Updated - - -

    Superb. I will explore this.

  11. #11
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    Couple of days after starting this thread, the way of my car decided to sag.. is 3 days after flushing the transmission fluid....

    overview_image_647552_942565.jpg

  12. #12
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    Quote Originally Posted by Hit Man X View Post
    Those strut mounts will run you about $500 for a pair. You should replace that expansion tank too as it looks a bit long in the tooth. You also have some wonky vacuum action at your pump there.

    The OE SLS is pretty simple on these, accumulator wise look to 80s MBs. 201 Cosworth. 560SEL and SEC. 70s MBs also had them. One of the members here rebuilds the pumps, the electronics seem pretty solid...just fluid flows but makes no pressure due to oring shrinkage.
    Hi there. Do you have alternate links or part numbers for the accumulators?

  13. #13
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    Quote Originally Posted by abdoul View Post
    Couple of days after starting this thread, the way of my car decided to sag.. is 3 days after flushing the transmission fluid....

    overview_image_647552_942565.jpg
    Attached Images Attached Images

  14. #14
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    No PNs, sorry. My system was mostly gone when I purchased my 10/84.

    Sag should just be bleed back in the pump I recall. My E32 V12 did similar until restarted.

    - - - Updated - - -

    No PNs, sorry. My system was mostly gone when I purchased my 10/84.

    Sag should just be bleed back in the pump I recall. My E32 V12 did similar until restarted.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  15. #15
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    I found some rear accumulators from Germany and receive them after 1 month's wait only to find out that my accumulated is actually okay.

    I still plan to overhaul them at some point

    Can anybody elucidate this mystery


    The PS reservoir is full but the rear is sagging nonetheless...

    What could prevent the fluid from reaching the rear? Do I need a new pump or something else?

    I noticed a very slight leak on one of the rear shocks. Can anyone refer me to a "hydraulic shock rebuilder" in the DC metro area preferably (but not limited to)?
    Last edited by abdoul; 09-29-2022 at 08:51 AM.

  16. #16
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    Jay Stratton can rebuild that SLS pump.

    As for the 'shock', call hydraulic shops. They are basically rams.

  17. #17
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    here is a link to the website of Jay Stratton https://www.bimmerforums.com/forum/s...-a-NEW-Website
    Shogun tricks and tips for the E32 series are HERE!

  18. #18
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    Thanks

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