LAD Suspension
Replacing the Dust Boot and Rubber Damper

Written by the backyard hack mechanic Sean750
Document history:
# 24 May 2003 added some comments from visitors
# 14 Feb 2003 initial version

Problem : this will not be the last article I will write about LAD. Although (at least from my perspective) the system is pretty well designed, you may encounter some problems with it. One serious problem is leaking of the rear hydraulic struts, caused by a leaking upper seal.

Premature leaking seals can be prevented by a dust cover in good condition. In my case, both dust covers where damaged. With normal gas shocks, I am not impressed and most of the time I leave it that way. But I do care about my expensive LAD shocks which where replaced about 50 dkm ago. Time to replace the dust covers and it addition, while things are apart, the rubber dampers.

Models : All models equipped with the LAD system (and not the EDC -electronic damper control- system which is a totally different system), although the procedure for the regular gas shock is identical, except the part about disconnecting the high pressure hose.

Remark: all long wheel based 7 series (735iL/740iL/750iL) where equipped with the LAD suspension. For the short wheel versions it was offered as an (expensive) factory option, but only for Europe and not for the US. Therefore you won't find a US spec 735i with LAD. Also, this story isn't applicable for the EDC shocks.

Folks familiar with the European car manufacturer 'CitroŽn' may see some
similarities with the suspension system used by this car manufacturer. The system is almost identical, although the accumulators are mounted separate from the struts, making this a bit different of the original CitroŽn system. Also the load levelling system on Mercedes Benz W124 stationwagon (1985->) uses this system. Some people report, although is isn't confirmed yet, that the Mercedes accumulators are identical to the BMW LAD accumulators and that they are much cheaper.

Lets start unbolting parts :

The hard part about the whole procedure is the fact that the rear seat backrest has to be removed, allowing access to the upper strut mounting nuts. This procedure covers the removing of the non-electrical backseats and headrests. This because my car doesn't have them.

Pull backseat up:

The rear seat back rest is mounted to the chassis with 4 plastic nuts. 2 behind the armrest so remove the Velcro covering the nuts:

Thus revealing the 2 armrest nuts:

And 2 nuts at the backrest corners (one visible here):

Next step is to remove both headrests (also non-electrical type). Pull them firmly up:

And remove the upper plastic trim of the backrest/seatbelts :

Leave the lower seatbelt connector attached and the plastic trim around the seatbelt, put plastic trim somewhere in lower backseat area and fully extend the seatbelt:

Pull the backrest up and away. You don't have to remove the backrest entirely:

Pull away the rubber cover, revealing the upper strut mounting. Don't unbolt the big center nut, but you can loosen it a turn while its still mounted in the car, making it easier later to remove it. Don't unbolt the 3 upper strut mounting nuts yet, but you can also loosen them a few turns:

Sometimes removing the speaker cover panel makes access to the bolts easier:

So much for the interior. Jack the car up from the rear, place jackstands, remove the rear wheels and depress the brake pedal at least 20 times to discharge the high pressure hydraulic (HP) system. In the wheel wells you should see something like this:

Several warnings in the factory manual and Bentley book can be found about the hydraulic high pressure system. So once again: absolute cleanliness is necessary when working on the HP system. When you loosen the nut of the strut, there is a high risk that debris (sand, mud, dirt) falls into the bore of the strut. That is not a good thing. So I cleaned things up:

And after that I cleaned it with some brake cleaner (or thinner):

Now unbolt the 14mm nut. I suggest you use a flare open wrench instead of a half-open wrench like I did:

The right side came easily (with some hammering) loose, at the left side I needed a big water pump plier, without damaging the nut to much. When loosening, a lot of Pentosin will leak out so use a bowl or something like that to catch the fluid:

Remove the HP hose, cover the hole with a small towel to prevent dirt getting in (protect also the loose HP hose with a towel):

Now loosen the big lower bolt (22 mm) of the strut (the oil stains are from the disconnected HP hose):

Now gently hammer the strut loose from the trailing arm, and support the trailing arm with your hand:

When the strut is loose, support the trailing arm with some wood or a jackstand. Don't let it hang loose:

Now unbolt the 3 upper mounting bolts in the interior. When loosening the last bolt, support the strut or it will fall right onto the floor or trailing arm:

For some bolts a swivel comes handy:

Gently remove the strut from the rear wheel well, do mind it's a bit heavy:

go to next page

If you would like to add any comments, remarks and/or corrections to this procedure, feel free to email Mike Oswald and we'll put it on our site. Share your experiences with us so others may benefit from it.