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750iL rear supension

Discussion in 'E32 (1988-1994)' started by eam3, Apr 28, 2010.

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    1990 750iL, 63K miles:

    One of the rear shocks started leaking, is it worth it replacing with another Sachs unit and keep the hydraulic suspension or is my father better off going to conventional springs and shocks? Car is barely driven now and will never be driven aggressively (especially in flat and straight Florida by an 81 year old). What's a good place to get the parts? How much can he expect to pay in labor?


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    People are actually pretty divided on this, so it's really a matter of choice.

    Very few places sell parts for the BMW LAD other than the BMW dealer and Dinan. Most dealer labor rates exceed $100 an hour, but I see little reason to go to a dealer when an independent BMW service center is just as experienced and will charge you generally less than the dealer will.

    Usually when the shocks leak, it's due to the breakdown of one, sometimes both seals inside the shock. This seal is very cheap, and if you are mechanically skilled, you can replace it in about an hour. The seals cost a few dollars each. I can retrieve the links for you if you think you can handle this job. The job requires you to disassemble the LAD shock, replace the seals, then reassemble the shock correctly. It's messy and time consuming, but not that difficult if you know what you're doing.

    You've got both pros and cons for both sides of the argument, and sadly, they're both right. It's basically a judgement call. Here's the lowdown:

    Retain stock self-leveling suspension:


    1) This is the way BMW engineered the long-wheelbase E32 cars. The car will automatically adjust the ride height in the rear to keep the rear end at the proper height no matter how much weight you have in the trunk. This way if you have a lot of weight in the trunk or in the backseat, your car won't look like it's dragging its rear body end behind it.

    2) The car will also adjust the rear end right height under high speed conditions for better handling and less wind resistance in the back. The self-leveling (from here on referred to as LAD, after the initials in the German proper name for it) pump is integrated with the Servotronic power steering pump and speed-sensitive steering system.

    3) There is also a built-in camber switch to warn you of an unsafe ride-height or rear camber position greater than plus or minus 5 degrees. The alert appears in the middle LCD display under your gauges in your instrument panel.


    1) It's a very expensive system to maintain, it's prone to leaking, and complicated to service. It also requires an expensive and specific type of hydraulic fluid that sells for roughly $12 per one liter bottle (the system uses around 5 to 8 liters). Older E32's used Pentosin 7.1. The newer E32's went to Pentosin 11S.

    2) If you're into optimizing your suspension or lowering the car, you're going to have limited choices, as the LAD system used different shocks and different springs.

    3) The unusual looking shocks, which look like regular shocks but appear to have a second piston or perch for the LAD system, cost around $500 to $1,200 each. Replacing the LAD steering pump is between $600 to $800. It's a dual-vane pump (sort of like two pumps in one: one for the power steering, the other for the LAD system)

    Convert LAD system to sport suspension:

    Alternately, it is possible to convert the car to use the conventional "sport" shocks and springs. Bavarian Autosport sells an LAD conversion kit for about $200 (does not include springs and shocks -- those must be purchased separately) and comes with instructions. This consists mostly of parts needed to bypass the LAD shocks, as well as plugs that allow the Pentosin to circulate through the rest of the system without LAD shocks. There is also an electronic bypass jumper so that you won't get a "self leveling system" error when you disable the camber warning switch.


    1) It's much cheaper than continuing to maintain the LAD system. Lets you use regular E32 shocks and springs. Wider choices of suspension options once the system has been converted.


    2) It's not possible to completely remove the LAD system without spending even more money than it costs to maintain it, since you would have to re-engineer the entire power steering system.

    3) Rest of the system left intact is still prone to leaks after you bypass it.

    4) Some LAD enthusiasts claim this hurts handling by "dumbing down" the rear suspension system. IMHO, I'm a bit skeptical of these claims, and there's been no evidence that a non-LAD e32 handles any better or any worse than one equipped with the system. The LAD system simply adds features and capabilities that some find useful, and others find to be an expensive white elephant to maintain.

    I have this system in my car and despite the expense, I have chosen to retain it as BMW intended. My car is a 1988 750iL and while my LAD shocks are fine, my LAD steering pump is leaking.

    Let me know what you want to do so I can help.



    P.S. If you do decide to retain the LAD system either by replacing or repairing the shock, it's a good idea to replace the bump stops and dust covers for the shocks also. These are relatively cheap parts and will prolong the life of your new or repaired shock. Also, if one is leaking, best to repair or replace both, as the other shock is probably in need of service soon also. Shocks and springs should be repaired or replaced in pairs, and to save you the trouble and expense of having to tear into the system a second time. Either way, you're probably going to need to top off your Pentosin too, so add that to your budget as well.

    No. Description Supplement Qty From Up To Part Number Price Notes
    01 REAR LEFT SPRING STRUT 1 05/1990 37121137025 $1,240.61
    01 REAR RIGHT SPRING STRUT 1 05/1990 37121137026 $1,240.61
    02 SPRING PAD LOWER 2 05/1990 33521131523 $7.48
    03 Additional shock absorber, rear 2 05/1990 33531137113 $20.55
    04 Support 2 05/1990 37121114729 $3.07
    05 SPRING PAD UPPER 2 05/1990 33531133048 $9.40
    06 Guide support 2 05/1990 37121129717 $47.70
    07 Pin M8X18 ZNS 6 05/1990 31331092886 ENDED
    07 Pin M8X18 ZNS3 6 05/1990 31336765744 $1.17
    08 WASHER-GASKET 2 05/1990 33521129567 $0.66
    09 Self-locking collar nut M8-8-ZNS 6 05/1990 31331092887 $0.58
    09 Self-locking collar nut M8-8-ZNS3 6 05/1990 07119904295 $0.36
    10 Plate 2 05/1990 37121130122 $4.41
    11 SELF-LOCKING HEX NUT M12X1,5 05 6 05/1990 32211095267 ENDED
    11 SELF-LOCKING HEX NUT M12X1.5-05 ZNS3 6 05/1990 32216769539 $0.83
    13 COIL SPRING 2 09/1988 05/1990 33531133502 $159.96
    14 Flat washer 2 05/1990 33521125260 $1.65
    15 Hex bolt M14X1,5X85 2 05/1990 07119914829 $5.82
    16 Control unit 1 05/1990 37141133481 $393.62
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    Thank you so much for the detailed reply. I'm leaving it up to the old man to decide but from what I gathered after talking to him is that he'll go with keeping the LAD. He got a quote for just under $1000 earlier today from the shop he regularly takes it to and that includes replacing the leaking shock (with a brand new Sachs unit), and all the other little necessities that go along with it. Not too shabby and hopefully the ride will return to how it used to be. I hadn't ridden in the car in a while but the last time I went out in it I did notice that the rear suspension felt very stiff - noticeably stiffer than my 330!
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    No problem. While your mechanic is at it, have him check the other one too.

    Since you mentioned a stiff ride, I am going to show you another possible cause -- but I have some good news here:

    Check the LAD air accumulators. Another messy job, but replacing an accumulator is a lot cheaper than replacing a LAD shock. The accumulator is part #1 on the diagram.

    Here's how to fix them:


    http://bmwe32.masscom.net Main site link (BOOKMARK THIS PAGE! Lots of useful DIY projects for your dad's 750iL)

    http://bmwe32.masscom.net/gavin/LAD_strut_rebuild.htm <== LAD strut rebuild (this guy rebuilt his leaking LAD shock for less than $20 in seals and O-Rings!)

    Autohausaz.com has LAD rear shocks for $534 and the accumulator for $134! that's $620 off the dealer price for the shock and a $58 savings off the accumulator's dealer price (nearly $700 in savings)! The link I provided above also shows how to rebuild the LAD shock if you want to attempt it.
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    AugustneverEnds 1988 325iS, 1989 750iL

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    My father had a mechanic attempt to bypass the LAD shocks on his '89 750iL years ago and it really wasn't a good idea. The car rode like a tank and the rear sag was noticeable. In the end modifying this system for conventional shocks is a big compromise and he couldn't live with it. He ended up replacing the shocks with OEM Sachs units and having the accumulators painted and rust-proofed. For future reference you might want to try Bavarian Auto Recycling (www.bmrparts.com) if you don't mind used parts. They have just about everything at prices way below list and have a guarantee against corrision on their merchandise for 12 months from the date of purchase. Cheers

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