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
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.
[ Help ]
'87 325es with all new sway bar mounts