discuss with me front suspension e30 vs. e21

As some may know, I recently picked up a '77 320i e21 for a winter project and am starting to think about what direction I'm going to go on the car. The one thing I'm kind of thinking about is the front suspension.

Whereas the e30 has the front control arm located by a balljoint on the subframe and the frame mounted bushing on the backside (with the front sway independently attached acting only as a swaybar), the e21 has a single-arm LCA located by a bushing on the subframe and using the swaybar itself as the second locating point. I suppose this is a "pure" MacStrut setup?

So how does this affect the movement action of the LCA? By my thinking, as the suspension compresses and the sway rotates, the angle change probably has a significant effect on caster, right?

Continuing on that, what effect does this setup have on handling (and on longevity/strength, for that matter) vs. the e30 setup?

I've seen that some guys fab up a kind of rod with spherical bushings moutned to the e21 frame to act as a second locator (using the swaybar attachment point) and then attach the sway in a more "conventional" arrangement (e.g. more like an e30). Thoughts on that?

Anyhow, just thinking out loud as I was researching the modifications needed on the subframe to fit my spare M42 into this car. But the car's out in the shed, in the dark, with stuff piled all around it....so I can't easily go "look" at things right now and am just visualizing things...

I haven't really looked into it personally, but the second attachment point should definitely help with how the suspension takes bumps. I had to learn how to handle those. It was just different.

I would borrow/get a pair of E30 struts and eyeball it.

FWIW I do have a pair but the springs are off...there's somebody probably closer than I am anyway.

The front suspension of the e21 is weird. BMW tried to be too smart for their own good I think. They are using the swaybar as a forward link. Which works fine as long as all the bushings are in tip top shape and properly installed. If not, like you say, you have problems with caster control and toe control (reason for the front end shaking these are known for)

irish44j said: I've seen that some guys fab up a kind of rod with spherical bushings moutned to the e21 frame to act as a second locator (using the swaybar attachment point) and then attach the sway in a more "conventional" arrangement (e.g. more like an e30). Thoughts on that?

That's the proper way of addressing the problem, because you're taking the problem out of the equation.

Or I would try to get some really rigid poly bushings for both the swaybar attachments to the car and the suspension arm. Or a hybrid, with a solid spherical bearing in the arm, and poly bushing for the frame mount.

I had my 83 lowered on Eibachs with Bilstiens and poly bushings with a double thick sway (forget the brand) and she handled like a dream. Granted it was only on Deal's gap and never tracked but everything seemed to work as intended.

I would think that the fore-aft movement of the spindle caused by the arc of the sway-bar/forward link would cause bump steer issues as well.

Does it?

shadetree30 wrote: I would borrow/get a pair of E30 struts and eyeball it. FWIW I do have a pair but the springs are off...there's somebody probably closer than I am anyway.

that's not really an issue since I also have an e30. Though not sure what good looking at the struts would go.

what I really need is a spare e30 subframe/LCA assembly to see if the entire shebang could be modified to work on an e21 :)

it's also a bit interesting that my '77 has different LCAs compared to other years of the e21, apparently. I'm not entirely clear what the difference is exactly, however.

That said, I do have a set of brand new ones on the way (got in straight trade for some other e21 parts that I don't need!)

Giant Purple Snorklewacker wrote:

so wait....is that black piece some kind of swaybar? I assume the rose-jointed drag link there is the locating arm - but attached to the same mounts as the sway?

more on this setup....custom or aftermarket?

In reply to irish44j:

It looks like a quick change aftermarket piece.......I have seen sways like that before, but for the life of me, I cannot remember where.

In reply to JamesMcD: Bump steer isn't really an issue with these, and they handle decent considering the unorthodox suspension setup.

irish44j wrote: so wait....is that black piece some kind of swaybar? I assume the rose-jointed drag link there is the locating arm - but attached to the same mounts as the sway?

It is the sway arm, yes. http://www.1speedway.com/Swaybar_Arms.htm

It allows you to run sprint car splined sways of any diameter you need - they slide thru a needle bearing in the aluminum block that also holds the front locating arm.

Here is the car it belongs to:

The rest of the info is here: http://www.davidmcintyre.org/the320.html

In reply to Giant Purple Snorklewacker:

I've never really wanted an E21...

...until now...

Another shot of the front suspension: