Self-Levelling Suspension

UPDATE: Thanks to SupplyantSimon (see comments) who has provided the answer, "A conversion kit is available from www.pedders.co.uk to convert the car to non-self-levelling. It works really well and saves you over £500".

Much confusion surrounds the Forester's self-levelling suspension and Subaru does little to enlighten anyone.

The issue is caused by the facts that the rear struts/shock absorbers on the Forester S Turbo made between 1997 and 2002 are self-levelling, they cost about three times the price of ordinary struts, making the cost of replacement around £800, and they are inclined to break.

The Forester can take a lot of luggage in the back and the struts' SLS valves do not seem to be able to cope with a fully loaded car with, in my case, three bikes on the back as well.

These are the facts as I understand them.

The 1997-2002 Forester is called the SF model. The SF S Turbo has self-levelling rear suspension. Other SF models do not.

The self-levelling suspension is completely contained within the strut and works by using the bouncing of the car when in motion to pump the strut to the right level. It is NOT adjustable suspension, like that on a Range Rover or BMW which usually involves an external pump controlled from the dashboard. No electricity is involved. If you heavily load the car, it will sag at the back, but, after you have driven for a kilometre or so, the struts should pump themselves up to the right level.

When the car is correctly supported the bottom edge of the car is parallel with the road surface and the space between the tyre and the wheelarch is much the same at the front and the back, about three inches. You can easily put your fist in the space.

Subaru Forester S Turbo with new SLS struts

Struts on earlier models are bright green and have an extra reservoir attached to the outside. Struts on later models, like mine, are black and have no reservoir. Both are branded Subaru Tokiko. Subaru replaces each type of strut with the same type suggesting, but not proving, that they are not interchangeable. 

The struts are not just shock absorbers and they incorporate some springiness of their own. Springiness is therefore provided by both the coil spring and the strut.

The use of self-levelling struts with inbuilt springiness allows the use of a softer coil spring than with a conventional strut. If you replace the SLS struts with conventional struts without changing the springs to a stiffer version, the car will ride several inches too low. Cars that ride like this either have struts with broken self-levelling or they have the wrong strut/spring combination.

Breaking the SLS part of the struts does not necessarily cause the struts to leak and they may continue to work properly as shock absorbers. This caused my non-Subaru garage to believe that there was nothing wrong with mine and to replace the springs instead. However there was nothing wrong with the old springs and they have now been put back on the car with new SLS struts.

It would, presumably, be possible for working self-levelling suspension to conceal sagging springs because the  struts would raise the car, if not heavily loaded, to compensate. However this seems unlikely an unlikely scenario because the springs seem very durable. Mine put up with broken self-levelling, and frequent bottoming out, for a long time. The struts seem to be the weak link.

Use of SLS struts with the wrong stiffer springs would presumably cause the car to ride several inches too high. 

There is much discussion about the use of non-SLS replacements because of the cost and reliability of the SLS struts. There is no doubt that, if this is possible, both the struts and the springs must be replaced together to ensure that the car rides at the correct height. I can see no reason why it should not be possible to use a non-SLS spring/strut combination from a non-SLS Forester or from a third party like often-mentioned KYB, but no authoratitive guidance is available.

KYB's website does not list any struts or springs for the SF S Turbo but it does list them for the SG S Turbo. The SG model was the post 2002 Forester shape so these are unlikely to suit the SF. (I was not aware that that there was an S Turbo version of this, but presumably there was.) When I have contacted KYB's technical help desk I have sometimes been told that there is a valid KYB replacement combination, and sometimes that there isn't. Other bloggers mention King Springs from Australia as a supplier but their website provides no specific information and they only seem to make springs.

Once I got confused, I found that Subaru UK unhelpfully passed me backwards and forwards between the parts department and the technical helpdesk. 

Although this does not provide the answer that anyone wants, i.e. details of an appropriate and reasonably priced non-SLS strut/spring combination, I hope it is informative.