From digest.v4.n708 Mon Jun 10 07:59:34 1996
From: "Rick Kjeldsen" <fcmk_at_watson.ibm.com>
Date: Mon, 10 Jun 1996 10:30:13 -0400
Subject: Re: Strengthening E30 M3 sport suspension

(When installing big sway bars...)
>I've heard that not stregthening the mounting points for the bars will
>eventually cause them to rip away.

No question about it. The worst problem is with the inner mounts up front. Stock, the bars attach to a flimsy tab off the back of the subframe. But because that is a known problem, most front bars come with a stronger mount that uses one of the subframe bolts as well as the tab. That seems to completely solve the front problem.

Soon after installing big rear bars almost everyone breaks the little triangle on the trailing arm that the bar end-link bolts to. Many bars come with triangular metal parts that are intended to be bolted on either side of the tab like washers. They help a little, but not much. The best solution is to have a welder re-enforce that tab with buttresses back to the trailing arm itself, as well as thicken the tab with an extra layer of steel welded on. You have to be careful because the brake line passes right under the tab. Overall it's an easy job because access is so easy (no need to pull the arm off).
The heat of welding will destroy the undercoating around the tab both inside and outside the trailing arm, so if you care about that kind of thing, be sure to re-undercoat outside, and spray some body-cavity sealer into the arm (the access hole is on the outside end where the wheel mounts, covered by a small plastic cap).

The second problem is less common. It seems to happen faster with setups having softer springs and stiff bars (street/track setups, rather than track-only setups), but I've seen evidence of it starting on nearly every tweeked E30s I've looked at that is run on the track. The inner sway bar mounts (to the car body) will flex, fatigue and eventually fail. I was hearing a loud popping when turning over road elevation changes for several months as the cracked mount would "oil-can" and the sound would echo through the car. Eventually it failed on a steep driveway and the bar ripped off completely. ("So THAT is what that noise was!!")
Unfortunatly it failed just a week before a track event!

To fix it you will need to pull out the sway bar and on the passenger side pull off gas tank filler pipe. (CAREFUL welding with that gas tank open under there!) You can comfortable work around the axles, diff, etc down there. It takes a little fabrication to build steel tabs to strengthen the mount. I found it best to just double up the existing mount with 1/8" steel on the "inside" (front) in such a way that left the bar bracket mounting area untouched. That let me use the old sway-bar brackets, and we didn't have to fabricate new ones. This will be tough to re-undercoat well because of all the corners and stuff, but if it's a street car be sure to do it, as it WILL rust (because of all the corners and stuff).

There is another alternative for the rear body mounts. Some tuners sell a re-enforced mounting bracket that bolts through the trunk floor as well as to the sway bar bracket. Costs over $200 from Korman. You have to add it BEFORE you fatigue the mounting point, it's not an after-the-fact fix. No experience with it.

rick
'87 325es with all new sway bar mounts
'88 M3
etc.