OK, I am assuming you tightened it down on the center strut bolt. Now, did you tighten up the adjustable portion sufficiently? If it is like other braces (I don't have one, so I am guessing a little here), it is not a solid piece, it has nuts on a threaded shaft to preload and adjust the brace, or bolts that allow for the mounts to move around for installation. These should be used to make sure it is good and tight once it is on the car.
For further info on the install of the SHO Shop brace, you can call their tech support line, which is listed on their site: 714-894-8415.
98 Silver Frost SVT
97 BMW 540I Sport, six speed
"Blue is for sky, black is for soil, and white is for simplicity, purity and hope for the future"
"A coveted car should never stunt your life, but should make it more rich and interesting."
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