Suspension Trouble Shooting

Post your E12 technical questions and comments here. Please, no off-topic posts.

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DCMotoring
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Suspension Trouble Shooting

Post by DCMotoring » Tue Feb 19, 2019 4:06 pm

Last summer my e12 started bottoming out while going over bumps and dips at moderate speeds. I replaced the front axle support bushings several years ago but did not get to the control arm bushings. Strut mounts aren't creaking and the car isn't bouncing. But the only thing I can think of is either the springs or struts/strut mounts.

I've got 17" style 5s on the car but have thought about going back to the OEM 14" wheels to help alleviate the issue but I'd still like to get to the bottom of it so I can get it fixed once it warms up a bit.

Any ideas? Thanks!

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528i-1981
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Re: Suspension Trouble Shooting

Post by 528i-1981 » Wed Feb 20, 2019 7:16 am

When you say "bottoming out" do you mean the undercarriage is scraping the road or do you mean the tires are impacting the fenderwells?

Maybe check your ride height to see if it's sagging any. Spec unloaded overall height is 55.9 inches.

I just replaced the strut inserts and the (OEM) springs on my E12, and while I was not bottoming out or rubbing with the original 14" wheels, the thing was a bouncy mess which didn't help the springs any. I can tell you that the car is riding probably 1/2" higher now.

For comparison, I'm measuring 27 1/2" from the ground to the top of the front wheel arch, but my overall height looks to be a little more than 56", so maybe mine is a little high.
(oo=00=oo) Eric
1981 528i Manual

DCMotoring
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Re: Suspension Trouble Shooting

Post by DCMotoring » Wed Feb 20, 2019 11:32 am

Tires on the fender wells. It also doesn't help that there wasn't much clearance to begin with!

That's a good idea to check the ride height. I did notice one side might be slightly lower than the other so might be time for new strut inserts and springs.

What kind of springs did you use? And I'm assuming you did the Bilstein struts? That appears to be the only thing available out there.

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Mike W.
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Re: Suspension Trouble Shooting

Post by Mike W. » Wed Feb 20, 2019 1:09 pm

I'm guessing you're rubbing in back, and guessing you have big 17s on there too, like maybe E39 size? 235/45-17? That's a big tire to try to squeeze in there without any modifications. I've got 225/50-16s on mine, 8" wheels in the back even and only rub under the most severe conditions, like literally with 600 pounds of concrete mix in the trunk. A modest roll of the fenders might help, that's not too invasive. One thing you can do to make it easy trying to figure out what's going on is unbolt the shock assembly from the semi trailing arm, with it in the air obviously. That way you can pivot it thru it's range of motion without trying to compress the spring and see exactly where it's hitting and how much. Granted things change slightly under weight and load, but it can give you a pretty good idea.

Assuming it's minor, you could go the route I did on my E28 when it was rubbing, again, only under extreme conditions. I made some 1/4" spacers to go under the springs and put a single piece of rubber on either side about a half an inch thick, I think it was a radiator mount off an E23, on top of the overload spring, that foam thing with a boot. Speaking of, is that there and what condition is it in? On the E28 it didn't look any different visually, but I eliminated rubbing.

Going back to 14s is a pretty drastic step, while I'm sure you can find something to go on there, but probably nothing more desirable than a 195/70-14 which isn't going to be very sporting driving wise. Not just adhesion at the limit, but you'll be having to crank an extra quarter turn of the steering wheel just on a freeway offramp. IMO 16" wheels are the sweet spot, either 205/55 or 225/50. But even on 17s if you have say a 225/45-17 it will be larger, but probably fit or be very close.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter

DCMotoring
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Re: Suspension Trouble Shooting

Post by DCMotoring » Wed Feb 20, 2019 1:27 pm

Strangely the back seems fine and the rear fenders are pretty clear of the tires. But the front fenders do rub the tires. I've had the car for almost 10 years and I didn't have any issues with the large tires (yes, I've got 235/45-17s) until about 5 years ago when the wheels started rubbing on the fenders at high speeds.

At that time I replaced a few really badly worn bushings and the scraped up tires and that seemed to work for a while, but the rubbing began again more recently but this time only over bumps and dips - not a speed.

Unfortunately I'll have to wait to really diagnose it because of the cold weather, but thanks for the feedback both of you! It gives me a couple areas to look at.

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Mike W.
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Re: Suspension Trouble Shooting

Post by Mike W. » Wed Feb 20, 2019 4:25 pm

And don't forget all tires of a given size are neither the same size nor the same shape. Some will be more of an oval cross section, some more of a rectangle. Don't forget the aux spring goes on the front too, if you're borderline that could make the difference.

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Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter

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maybeillbuyit
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Re: Suspension Trouble Shooting

Post by maybeillbuyit » Sat Feb 23, 2019 12:51 pm

Mike W. wrote:
Wed Feb 20, 2019 4:25 pm
And don't forget all tires of a given size are neither the same size nor the same shape. Some will be more of an oval cross section, some more of a rectangle. Don't forget the aux spring goes on the front too, if you're borderline that could make the difference.

Mike, as usual all very good info on tire sizes etc. Your recommendations for 16 in tires is exactly what I just installed on my staggered BBS RAs. Although I haven't driven much due to the crap weather, no problems so far
In your comment above you say " aux spring" . Same thing as bump stop? I haven't heard the term aux spring before.
1977 530i another project
1979 635csi Euro "project"
1987 635csi

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Mike W.
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Re: Suspension Trouble Shooting

Post by Mike W. » Sun Feb 24, 2019 1:13 am

maybeillbuyit wrote:
Sat Feb 23, 2019 12:51 pm

In your comment above you say " aux spring" . Same thing as bump stop? I haven't heard the term aux spring before.
Yeah, I've seen it referred to as a variety of things. I've seen the aux spring description in some manuals and I think it's BMWs nomenclature.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter

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528i-1981
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Re: Suspension Trouble Shooting

Post by 528i-1981 » Sun Feb 24, 2019 7:44 am

If replacing with Bilstein B6, which have internal bump stops, do you think there any additional benefit to including the aux spring?

Here's a link with pictures showing the internals of a Bilstein strut cartridge and the internal bump stops.

https://legacygt.com/forums/showthread. ... mp;t=99244

This link explains how to cut down the internal bump stop when using lowering springs on modded Subaru Legacies. If the valving on B6s and B8s is essentially the same, then this could be part of the solution if B8s are NLA.
(oo=00=oo) Eric
1981 528i Manual

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Mike W.
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Re: Suspension Trouble Shooting

Post by Mike W. » Sun Feb 24, 2019 1:24 pm

528i-1981 wrote:
Sun Feb 24, 2019 7:44 am
If replacing with Bilstein B6, which have internal bump stops, do you think there any additional benefit to including the aux spring?

Here's a link with pictures showing the internals of a Bilstein strut cartridge and the internal bump stops.

https://legacygt.com/forums/showthread. ... mp;t=99244

This link explains how to cut down the internal bump stop when using lowering springs on modded Subaru Legacies. If the valving on B6s and B8s is essentially the same, then this could be part of the solution if B8s are NLA.
If you're actually bottoming out, yes, I think there is benefit to the aux spring. If not, no.

Interesting on the link, I had no idea the shocks came apart that way.
Mike W.



1980 528i, 3.5 euro, 5 speed conversion
1981 528i, 3.6, Recaros and more. Project
1998 328is, quick and efficient, but not satisfying
2000 528iit, Vacation mobile/wife's grocery getter

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