BMW E28 Rear Sway Bar Bracket Reinforcement/Fix

If you install aftermarket sway bars on your E28, there may come a time when you hear a thunk/clank/bang from the rear axle area and suddenly have lots of understeer. Congratulations -- you have just ripped off a rear sway bar mount! Hopefully, you won't be in a hot turn at the track when it happens. I was lucky that mine let loose as I went over a speed bump in the parking lot at work. That was merely the straw that broke the camel's back -- the real damage was done during aggressive street driving and numerous autocrosses, particularly the seven runs I'd had the day before at the Michelin Proving Grounds in Laurens, SC.

A big factor in the mount failure was that I had my LaJolla Independent/Suspension Techniques rear bar set at the stiffer of the two settings, causing the end link to sit at about a 15° angle. While the stock bar imparts forces that are mostly vertical on the mounts, this angle imparts about 25% of the force in a fore-aft direction which the stock mounts don't have the capability to handle.

The Damage

The pics immediately below are some quickie scans I did of the original bracket and my scheme for fixing the damage. Note that the metal fatigued around the four spot-welds that hold the bracket on. Even though my car is virtually rust-free, you can see that there had been a bit of surface rust between the bracket and the crossmember, where neither the factory electrocoat nor the undercoat had penetrated, giving water a place to relax.

    

  

The Fix

I obtained a good bracket from Strictly German. I didn't get just the bracket, but cut out a section of the crossmember that the bracket was welded to. I cleaned the grunge off the backside of the crossmember section, noted the marks where the spot-welds were, and ground the spot-welds off from the back side. Once the metal was thin enough, I snapped the bracket off the crossmember and ground the rest of the welds off the bracket.

I also ground the two small corners off the back edge of the bracket so that the rear plate could be welded straight down the back and hold the small strip of metal where the tab on the sway bar bushing fits; this is a common area of failure as well.

I got the repair metal from McMaster-Carr and chose P/N 6544K12 - 1006/1020 Carbon Steel Sheet 0.0625" Thick. My reasoning for this material thickness was that it was only slightly thicker than the bracket itself and thus the pieces would weld easily. This logic was good for the loose bracket, but not as good for the one that was still on the car -- more on this later.

My Dad has a TIG welder, and his good buddy Jeff is an aerospace welder by trade, so I asked Jeff to do the welding for me. (Most folks think my Dad and his buddies have unusual tastes in automobiles.)

Here's the bracket after Jeff welded the plates on and as he trial-fit the assmbly to the car.

    

The installation went as I expected it to, with one exception:  the tip of the TIG was too big to make a weld on the outside edge of the plate on the front of the crossmember. We could have broken out the gas welder, but figured that the bracket wasn't going anywhere. I made sure to seal that crack with brushable seam sealer.

  

I painted the repaired area with Eastwood Chassis Black. To get the paint into the crevices between the plate and the front of the crossmember and between the bracket "ears" and underside of the crossmember, as well as inside the bracket itself, I used an undercoating nozzle with a small-diameter wand and sprayed until paint dripped out.


Results

Ahh! Neutral handling after nearly six months of understeer! I certainly won't be worrying about ripping off another rear sway bar mount. Now I have to worry about the front!

Notes

Beware Cosmolene -- expect lots of wax fires inside the crossmember. Thankfully, they blow out easily with a blast from an air gun.

In stock form, the front edge of the bracket sits back about 1/8" from the front of the crossmember. Having the plate on the front as shown here made the bracket flush with the front of the crossmember. However, the other side was still intact, so I made a slight s-curve in the front plate to account for this. Perhaps this 1/8" stagger of the brackets would make a difference on a high-dollar race car, but I doubt it matters on an E28.

The 1/16" (0.0625") plate thickness I picked worked well for the loose bracket, but not as well for the bracket which was still on the car. The awkward position of the bracket made it a bit difficult to weld, and there was burn-through in a couple of spots. Jeff's recommendation is that the plates be thicker, so that the welder can "burn in" from the thicker plate to the thinner bracket. 3/32" (0.0938") might be a good choice if one can find it.

Shawn D.