The front strut towers on an E36 or E46 are notorious for cracking, for the same underlying reason the rear subframe mounts tear out of the floor: thin sheet metal being asked to carry loads it was never sized for. Front and rear are two ends of one problem, and cars that have suffered one are worth checking for the other.
This one had cracked badly, twice.
Why they crack
Every load the front suspension generates — bumps, kerbs, braking, cornering — is fed into the shell through a fairly small area at the top of the strut. On a standard car with standard springs and a rubber-mounted strut, the tower copes.
Two modifications change that, and most cars that crack have both:
- Stiff springs. A softer spring absorbs energy on the way in. A stiff one passes more of it straight through to the tower, and more of it arrives as a sharp spike rather than a gentle push.
- Camber plates. Replacing the rubber top mount with a spherical bearing removes the last piece of compliance in the load path. Nothing is left to soften the hit.
Neither is a bad modification. They are both the right call on a track car. But together they change what the strut tower is being asked to do, and a stock tower was designed around the assumption that a rubber mount was doing some of the work.
The camber plate detail that actually did the damage
This is the part worth knowing, because it turns a slow problem into a fast one.
The car came in with cheap aftermarket camber plates, and the design was poor in one specific way: the edge that bore against the strut tower was sharp. Not radiused, not flanged — a hard edge.
That effectively turns the top of your front suspension into a knife. Every bump does not just push on the tower, it presses a sharp edge into thin steel. The metal does not have to fatigue over years; it gets cut. On this car the result was two cracked strut towers.
So when you are shopping camber plates, look at the face that contacts the tower. A plate that spreads its load over a broad, smooth area is doing the job. One with a small, sharp contact patch is a slow-motion hole punch, and the money you saved buying it will be spent on bodywork.
Cracks found and marked, then the area stripped back so there is clean metal to work with.
How to check yours
Open the hood and look at the top of both strut towers. It takes a minute:
- Cracks radiating from the strut mount holes, or from the edge of the camber plate where it bears on the tower.
- Metal that looks dished or dented around the mount, as though something has been pressing into it.
- Cracked or flaking paint in a line. Paint splits before you can see the metal underneath separate, so a suspicious line in the paint is worth cleaning back.
- An alignment that will not hold front camber between sessions.
Check both sides. Cracking is rarely symmetrical, and finding one good tower proves nothing about the other.
The repair
We use BMW-sourced strut tower reinforcement plates, which can be bought at the dealer or through us.
Most people simply place these plates between the camber plate and the bottom of the strut tower, and that is usually adequate — it spreads the load and stops the problem getting worse. If your towers are sound and you are fitting coilovers, sandwiching a plate in is cheap insurance and we would not talk you out of it.
This car was past that. It already had two cracked towers, so we went further and rosette welded the plates to the strut towers instead of leaving them as a clamped sandwich.
Plates welded rather than sandwiched. Same rosette method we use on the rear subframe plates.
Why weld the plate on
Three reasons, and the second one is the one people do not expect:
- It is structural rather than clamped. A sandwiched plate only works while the mount is torqued down onto it. A welded plate is part of the tower whether or not anything is bolted through it.
- It makes future suspension work easier. The reinforcement stays put when the camber plate comes off. You are not juggling a loose plate every time the strut comes out.
- It adds structure to the tower itself, rather than just protecting the contact face.
This is the same approach we take with rear subframe reinforcement plates — fill the rosette holes, keep the heat controlled, leave a flat mating surface behind.
Welding the cracks
The cracks themselves were TIG welded, slowly and carefully. Slowly matters: thin sheet warps, and a crack repair that pulls the tower out of shape has moved your suspension mounting point, which is a worse problem than the crack.
Our goal on a job like this is that the tower looks, at first glance, as though the damage never happened. On this car the damage was severe enough that it was not quite possible. We are telling you that rather than only showing you the cars that came out perfect.
Welded, dressed and painted.
Related chassis work
- E36 rear subframe reinforcement — the other end of the same car and the same problem. If the towers have cracked, look underneath.
- E46 rear subframe reinforcement — the best documented of the family.
- Z3 rear subframe reinforcement — a different failure again, this time at the differential mount.
- Rear coilover loads on an E46 — more on where suspension load actually goes.
Cracked towers, or fitting coilovers?
If your towers have already cracked we will repair and reinforce them. If you are about to fit coilovers and camber plates on a sound car, tell us — adding reinforcement while the struts are out is far cheaper than doing it after. We also have alignment and corner balancing in-house, so the car gets set up properly before it leaves. Call (949) 667-4397 or send us a quote request.
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