4 door with SLS

[cornershop]

Hi all

I’ve recently become the owner of a 1991 525i m50 saloon/sedan. Quite rare to have SLS on a 4 door (non-m5) I’m led to believe and from what I’ve read, most will delete SLS when problems arise.

I’m keen to stick to the original specification and so looking to refresh SLS (rear only). The front has just been lowered 25mm by my local garage with Eibach Pro Kit springs on new Sachs dampers, top mounts with new drop links and ARB bushes all round.

I have ordered a pair of refurbed SLS struts from Nagengast.

I want to fit H&R -10mm rear springs to line up the ride height with the Eibach fronts, however these are listed for Touring only (if I’ve read the below links correctly) are they likely to be compatible with the 4 door?

https://www.venommotorsport.com/partcode/29888-1/

https://www.driftworks.com/h-r-29888...pring-kit.html

Can anyone confirm if they Touring SLS springs will fit my 4 door?

Thanks all

[eddycooper]

Since you're staying with SLS, you actually have the ability to set your rear ride height (to some degree) with the SLS system itself. The rear sway bar has a little arm attached to the SLS valve and its clamp can be adjusted to set your ride height. If you have a repair manual that includes the SLS system, it should show you how - you would just choose a lower ride height than stock. So it might be worth starting there before investing in new springs.

That said, the Eibach springs will be firmer than stock so the mis-match of spring rates between front and rear may not be what you want. I don't have any suggestions for aftermarket springs to go with the SLS. But there are likely some BMW options available (eg. M5 springs).

Finally, your car has a ride height sensor/switch and you might need to disable that switch to eliminate warning messages on your dashboard. It gives a warning if it thinks your SLS system isn't working or is overloaded (ie. if your suspension is too low).

[cornershop]

6C1893AC-B34A-4596-877D-5BF7ED388883.jpeg
This is what it sits like at present with eibach -25mm fronts and standard 29 year old rears

[cornershop]

Thanks Eddy - I read that lowering using the rear sway bar lever was not the best way as you lose suspension travel hence me considering using lowered springs. I will investigate both options.

im hopeful the Touring springs are a straight swap; whilst I’m there I will get the garage to do a full check of the SLS setup.

I read there is a lowered SLS strut option but finding a used set would take some time, I imagine. These come with lowered springs and I believe shorter strut bodies although I could be wrong in the last point.

Appreciate your feedback

[moroza]

SLS springs are softer than non-SLS for the same model. However, all E34 rear springs are identical as far as fitment to the rest of the hardware. This means there are certainly some E34 springs that are stiffer than stock SLS, but not as stiff as non-SLS H&R.

I had Eibach front springs with stock 530i Touring rear springs (stiffest non-M E34 rears that I'm aware of), on a 530iT missing about 150lb. It seemed an alright combination. My hunch is that with Eibach fronts, you might want non-SLS 525i saloon rears.

[cornershop]

Thanks for your input - really useful to know I can use non-SLS springs if required.

I will see if I can find more info on the HR springs I’ve linked above - I don’t mind a firmer ride, but don’t want anything harsh.

[cornershop]

So I bought some H&R 29579-1 springs having read elsewhere they are the RoW equivalent of m5 SLS compatible 29579 springs - wrong - they are not SLS compatible.

Im about to hit Go on some 29579 springs from Bimmerworld but have hesitated due to potential weight differences between the 2 cars. Some sites have the US m5 listed as 1725kg? Versus 1480-1550kg for my 525i M50. Unsure whether im correct to think most of the weight difference would be upfront in the engine bay area , and the rear (ie the springs I need) should be similar to my 525i.

Anyone care to comment?

[moroza]

An M5 rear will be heavier than an M20 E34 rear. The transmission, brakes, diff, and minor bits all add up.

[consti2tion]

An M5 rear will be heavier than an M20 E34 rear. The transmission, brakes, diff, and minor bits all add up.

Maybe I'm think about this wrong but, the weight of the brakes would have no effect on the springs of the car? But no matter the trans and diff would certainly add weight.

[moroza]

Yes, brakes would affect total mass but not sprung mass, and therefore not spring rate (at least as far as static load is concerned). The rest does add up, though.

[cornershop]

Had an interesting email exchange with the very helpful Yvonne at H&R in Germany - she advised that the 29579 and 29579-1 springs are the same, even though in Europe the -1 denotes its for cars without SLS. Of course, i established this after placing an order for the SLS friendly 29579 spring kit. 🙄

[lonestar22]

6C1893AC-B34A-4596-877D-5BF7ED388883.jpeg
This is what it sits like at present with eibach -25mm fronts and standard 29 year old rears

the ride height looks perfect in this photo. why lower the rear? it would be uneven.

[cornershop]

the ride height looks perfect in this photo. why lower the rear? it would be uneven.

Fair point - I’ve got newly refurbed struts from Nagengast - refitting 30 yr old springs to new struts doesn’t sit well with me; I’m also thinking new factory SLS springs would raise the rear compared to 30yr old springs, so I’m hoping -10mm will even the ride height front to rear.

Suitability is hypothetical as Yvonne at H&R could not guesstimate the effect of using M5 springs on the rear of a 525i

[moroza]

If they aren't rusty or yielded, there's nothing wrong with using decades-old springs.

[polov8]

If they aren't rusty or yielded, there's nothing wrong with using decades-old springs.

Being in the UK, it's a good bet they look like they've been on the wreck of the titanic for the last century! Spring breakages are a regular occurrence here, so renewing 25 yr old ones is always a good idea.

[cornershop]

Being in the UK, it's a good bet they look like they've been on the wreck of the titanic for the last century! Spring breakages are a regular occurrence here, so renewing 25 yr old ones is always a good idea.

my thoughts too - let’s see what it looks like with the m5 springs. If the a** is in the air, I will rethink

[cornershop]

Just collected the car and I’m happy with the way it’s turned out.

Recap - front Sachs shocks and Eibach -25 mm springs
rear - refurbed SLS struts 1137675/676 with M5 spec (SLS) rear springs with -10mm drop

i will let things settle and drive for a few hundred miles - I may drop it a few mm more at the back.

- - - Updated - - -

The new spheres, struts and fluid have really improved the ride which was a touch too firm before. I’m wondering if the spheres were at fault. Unsure, regardless, it feels way better now. Compliant and comfortable - perfect.

[moroza]

You're aware that rear ride height is adjustable with SLS?

[cornershop]

You're aware that rear ride height is adjustable with SLS?

Yes indeed - there is a one finger gap between arch and tyre which is spot on - will monitor over the next few hundred miles.

over a familiar route last night which I know would normally bounce the car around, it was so much better planted. The rear setup was very much in need of attention.

[cornershop]

So I have driven the car for about 500 miles since having the work done. The car feels great, and I love driving it.

One issue I’ve encountered however, is fluid forcing its way out of the SLS/pas reservoir.

Level checked from cold, it was 5-7mm above the gauze
Took it for a 30 minute drive, and rechecked - now 5mm from the top of the reservoir, with signs of overflowing. Checked on level ground but the driveway is on an incline, which is when it spills over.
Use a syringe to remove c.50ml, to bring it down to 10mm above the gauze.

Leave it for several days, then take it out and it does pretty much the same thing. Less overspill, I guess due to lowered level from the previous overspill.

1) Chatting with a e34 m5 specialist, he advised chfs should be just below the gauze, so maybe I was overfilled from the outset?
2) if fluid level 5-7mm above the gauze is acceptable, what could cause the fluid levels to change? The specialist suggested a NRV in the SLS valve could have failed, allowing fluid to head to the reservoir. He has internally rebuilt e34 SLS valves on the shelf, but when I suggested a new e38 valve could be used (?), he thought that would be my best option

3) The ride height appears static, ie at the correct level, and has not changed even after the fluid loss - does this suggest the valve is ok - perhaps the system needs to be bled? I can’t get hold of the specialist that fitted the struts and accumulators to confirm what they did.

4) has anyone used a e38 valve on an e34? Is it really just the bracket that needs to be swapped over?

apologies, lots of questions - can anyone help?

- - - Updated - - -

7772F3B4-9CAC-49F5-9A61-6C4CC14B2750.jpeg
Sits nicely...

[cornershop]

I’ve completed another 500 miles - fluid levels have settled at just under the gauze.

Ride heights are about right visually (not measured them).

Comfort levels are spot on - hopefully nothing further to report.

EE160580-4939-4DC5-A60C-453D3868FA47.jpg

[moroza]

I'm sorry I don't have answers to your questions, but I just got my SLS retrofit working, and I'm having a bit of the same confusion as you regarding fluid level and full bleeding of the works.

Also a lot of the same appreciation for what appears (having done one test) to be a significant comfort improvement.

I also have an issue with my ride height, where the SLS spring is only slightly softer and actually taller than the non-SLS it replaced, resulting in the unladen ride height taller than before and above the SLS set point. Do you have or can you get dimensions for your rear springs?

[cornershop]

I'm sorry I don't have answers to your questions, but I just got my SLS retrofit working, and I'm having a bit of the same confusion as you regarding fluid level and full bleeding of the works.

Also a lot of the same appreciation for what appears (having done one test) to be a significant comfort improvement.

I also have an issue with my ride height, where the SLS spring is only slightly softer and actually taller than the non-SLS it replaced, resulting in the unladen ride height taller than before and above the SLS set point. Do you have or can you get dimensions for your rear springs?

Sorry, can’t help with spring measurements or dimensions.

Did you see this thread on another forum - I’m SierraPapa - it details my exchange with Yvonne at HR (i can provide her direct email address if you wish, she was very helpful.)

https://www.m5board.com/threads/expe...9/post-7612390

[moroza]

Interesting, but a bit confusing regarding what springs she's talking about exactly.