Self Levelling Suspension replacement

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nagaro635
Posts: 130
Joined: Tue Apr 05, 2011 4:12 am
Location: Sydney, Australia

Self Levelling Suspension replacement

Post by nagaro635 »

Guys,
I know this subject has been mentioned plenty of times but I need help. I have an 88 E24 with Self Levelling suspension. The problem I had was that the left top shock mount was badly worn and creating all sorts of noises. The rest of the SLS was fine however I could not source any replacement shock mount in Australia. So on the spur of the moment (which I now regret) I decided to remove the SLS altogether and go for a standard setup. How hard can it be right??? bad idea !!

I presumed that all I need to do was buy standard strut mounts with standard shocks. No, the standard strut mounts are smaller in diameter and therefore my spring wont fit. Also the standard shock spring mount is smaller and also flat based. This meant that my SLS coils do not fit. So I started looking for a standard coil with tapered ends. My other problem is that the car was lowered 1 inch all round.

With this in mind I decided to assemble the old strut etc (out of the car) and with this, and the new shock and new strut mount in hand I went to a spring maker. I asked the guy to make new coils that will give me the same ride height and spring rate of the old setup.

I am now worried that when I put the new arrangement back in the car that the rear will sag. I have just been told that the SLS coils are soft and the adjustable Shock of the old setup was designed with a heavier damper. is this true??

Should I get the new springs with a stiffer spring rate to counter this possible sag. The cost to get these coils made up are $375 and im now worried that I will have a real soft rear end that will sag. Have I done the right thing in ordering the new springs t have the same ride height and spring rate as the old SLS coils?

John
John
Sydney
Australia

1988 BMW 635csi - 'Glamour Machine'
BMW E46 M3 (Manual)- 'A shot in the arm'
2003 Nissan Maxima- 'work aholic'
davem6
Posts: 81
Joined: Thu Aug 13, 2015 1:06 am

Re: Self Levelling Suspension replacement

Post by davem6 »

Hi John
I remember seeing an SLS removal kit advertised some time ago, I think it was at Bavauto, but have not been able to find it again for you. The kit included new shocks, springs and spring mounts. It sounds like you have most of these parts now anyway. It should be easy enough to find a pair of spring seats off an E28, try Addam Smith or Joe Chabake.

When I got my car the SLS had already been removed and the back shocks replaced. It always sat way too low in the back and was too soft and would hit the bump stops. I bought a set of H and R springs for the back and they seem good, Cam is using these in his car too. The rear height can be adjusted by moving the spring clip in the grooves on the shock, the down side being that you have to pull the spring up off the seat to get at the circlip. I finished up making a set of adjustable height bottom spring mounts similar to front coil over shock arrangements so that I can adjust the ride height just by jacking the car up and using the C spanners. I machined a new circlip groove in the shock lower down for the threaded tube to bear on and the spring seat sits on the nuts.

Rather than having custom springs made I think it is better to go with a tried and true solution such as Eibach or H and R so you get the right handling without destroying the ride quality. These springs will cost less that the prices you have quoted for the custom ones.
1987 M6
NSW Australia
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Brucey
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Re: Self Levelling Suspension replacement

Post by Brucey »

that is a lot of money for a couple of springs to be made!

Since you have nearly all the parts required to fit the standard springs on standard shocks, and the knackered SLS top mounts were the problem you started with, I suggest that you just buy the correct (standard) top mounts and get some readily available springs to give you the ride height that you want. Whether you use Bilstein B6 or B8 shocks there are height adjustments possible via grooves in the shock body. The top mount is a commonly used part that fits various other BMWs too, IIRC. If you get some used ones they can be refurbed by pressing in new rubber bushes.

If you still get the wrong ride height, it isn't difficult to cut, extend and reweld the lower spring perch to get the ride height spot on, or within the adjustment range anyway.

BTW when you build these shocks up, don't forget to buy and fit new BMW bump stops and to fit the correct protection tubes to them; the SLS shocks may not have had these parts and anyway they might be knackered. There is a choice of bump stops from BMW; if you are shooting for a 1" drop then you need the one that is fitted to M635CSi models, which is a bit shorter than the standard one.

BTW on the subject of SLS shocks, Boge supplied similar shocks to Volvo in the 1980s. These could be configured to be manually adjustable, so that a rocker switch on the dash drove the pump etc to raise and lower the rear suspension. I have often wondered if the BMW system could be reconfigured to work in a similar fashion; a common fault is that the ride height sensor goes bad on the BMW arrangement and this causes the whole system to stop working.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Brucey
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Re: Self Levelling Suspension replacement

Post by Brucey »

Also it isn't difficult to work out the spring rate of the original springs. Elsewhere on this site you will find a listing of rear spring rates (*).

There is a lot of nonsense spoken about spring rates on E24s BTW. The fastest way to ruin the ride quality and reduce rear end grip (especially on bumpy roads) is to fit springs that are too stiff, coupled with dampers that have standard damping rates in them. Yes you can improve things if your plan is drive like a loony around a smooth race track but this involves buying more than just springs.

Even the M635CSi rear springs are only a little bit stiffer than stock springs.

(*) NB the data on stock springs is often misleading. The OEM BMW ones have a progressive wind to them; this means that at full droop you might start with seven active turns (say), about six active turns at normal ride height, but by the time the springs are compressed to ~2" of bump (from normal ride height) you might only have four or five active turns. This might turn a nominally 180 in.lb spring into a 250 in.lb spring where it matters (i.e. on the outside wheel in hard cornering; Note that the correct length bump stop provides additional compression damping here and is an integral element in the suspension system ). Very many aftermarket springs do not have a progressive wind to them, and thus have a poor ride quality most of the time yet don't offer any benefit in hard cornering.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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nagaro635
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Joined: Tue Apr 05, 2011 4:12 am
Location: Sydney, Australia

Re: Self Levelling Suspension replacement

Post by nagaro635 »

Thanks Guys for all your input, much appreciated. i had the coils made up and made my own rubber seats and sourced new dust covers and bumper stops. I put them all in, and to my great relief its absolutely perfect. Ride is great and handling excellent. The ride height is as it was and the car sits perfectly. What a relief. Many thanks :D
John
Sydney
Australia

1988 BMW 635csi - 'Glamour Machine'
BMW E46 M3 (Manual)- 'A shot in the arm'
2003 Nissan Maxima- 'work aholic'
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