Broken shock tower

A while back, I added some sport shocks to the Bimmer, and they're pretty stiff. I love the way they make the car handle- it drives like a 3600 pound go-kart.

Unbeknownst to me, BMWs have notoriously weak well-engineered shock towers. I'm sure they're manufactured to exact tolerances that make them last exactly 500,000 Km with stock shocks, but with stiff go-fast shocks, they pretty much just fail.

There's a speed bump near my house. I drive over it every day. As you might expect, I've gotten used to it, and I don't really slow down for it anymore. Well, one day I went over it with just a little too much vigor, and *POP*, the bolt heads that hold the shock mounts pulled out and ripped a nice hole in my driver's side shock tower:

Hole ripped out of shock tower

So, I'd like to give you a quick step-by-step of how to fix this if it happens to you.

I should mention, this repair was done on my beloved 1998 e36 BMW M3, but this procedure would be identical for just about any BMW coupe or sedan. It would be very similar for any other BMW.

Other brands of vehicles would also be similar, except that you may not be able to purchase a new shock tower insert from the dealer. If this is your situation, then your best bet is to try to cut an entire shock tower off of a car from the wrecking yard...but I digress.

Tools:

  • Welder
    • (MIG, TIG or Oxy-Acetylene Torch with a #1 welding tip and steel wire/rods.)
    • Optionally, if you don't have access to a welder, you could use 1/4" steel pop rivets with backing washers, but I'm not going to cover how to do that here.
  • Propane torch or heat gun
  • Old towels or rags, and a bucket of water
  • Drill (My 18v cordless drill worked...just barely)
  • Spot weld cutter bit
    • Harbor Freight has one for really cheap that worked for me. It's part number 63657. It obviously wouldn't last if you're trying to do this for a living, but it will work for this one job.
    • If you can't find one of those, a step drill would also do the trick.
  • Hammer
  • Centering punch
  • Angle grinder
  • Wire brush
  • Screwdrivers for removing carpet and panels from trunk
  • Wrenches/Sockets for removing shock mounts and shocks
  • Safety glasses

Parts and Supplies:

  • New LEFT SIDE shock tower insert, BMW Part #41 14 8 169 027, or ECS Tuning part #69796
  • Shock mount reinforcement plates. Not required, but highly recommended! I bought these ones from ECS Tuning: part #ES2642687 Really, any cheap eBay ones would probably work fine.
  • Shock mount Pelican Parts #33-52-1-137-972-BOE
  • Sandpaper
  • Lacquer thinner or pure denatured alcohol
  • Bare metal primer
  • Paint
  • Spray underbody coating

I got a new shock mount because, when mine ripped through the shock tower, it got pretty mangled. You might be able to reuse yours.

Step 1: Remove all the carpet, plastic covers, anything else that's in the way.

Step 2: Remove the shock and shock mount

Step 3: Scrape or grind away the coating from underneath. This doesn't have to be done very neatly. The idea is to remove enough so that the coatings don't glue everything together.

Step 4: Grind / sand / scrape away the paint and sound dampening coatings. The idea here is that you need to be able to see where all the spot welds are.

Step 5: Drill out all of the spot welds. Use the hammer and center punch to make a dimple in the center of each spot weld, then use your spot weld bit or step drill to drill out the welds. Drill carefully, to make sure the welds are removed completely. Removing a little bit too much metal from each hole is better than not removing enough, but don't overdo it.

Step 6: Tap the shock tower insert carefully with a hammer to remove it. Pay attention to any spots that seem to be "hanging on" and drill or grind them out as needed. Don't hit hard- be careful not to deform the metal.

If the insert doesn't seem to want to budge, it might be glued in place with underbody coating and paint. Use a torch or heat gun to heat up the entire area while you tap with a hammer. Eventually, it will fall out.

Step 7: Temporarily install your shock and shock mount to hold the new insert in place. You could also accomplish this with a couple pieces of tape, or a small self-tapping screw, or an assistant holding it in place from underneath. Position it by eye to get it as close as possible to the same position as the original.

The parts should fit as closely as you can get them. You may need to get creative with the hammer to make the old shock tower the correct shape to fit the new insert perfectly.

Use a marker to mark all of the holes, and also make some alignment marks so you can get it back into the same position later. I'm using a black Sharpie here, but a metallic silver Sharpie or a paint pen would work a lot better.

Your alignment marks can just be a couple lines drawn on the car and insert that you can use to line things back up later.

Step 8: Remove the shock, shock mount, and shock tower insert. Use your grinder or some coarse sandpaper to remove the paint on all the spots you marked with the marker. You need bare metal in all those spots. (Sorry, I didn't get a photo. Here's some dude grinding metal instead...)

Image result for grind paint from metal

Step 9: Put the shock tower insert back into position, line up your alignment marks, and weld all the drilled out spots. You could grind them flat if you want it to look pretty- I didn't care that much.

Note that I'm using wet towels to protect the wiring and carpeting in the trunk that couldn't be removed.

Use a wire brush and sandpaper or emery cloth to clean up the area. You want to remove all the burned paint residue and oxidation. Then, clean the area up with a paint-compatible cleaner, like denatured alcohol or lacquer thinner. It's not going to be show quality paint, but we want it to stick and protect from rust.

Step 10: Coat the top and bottom with bare metal primer. Use multiple coats if needed.

Step 11: After the primer dries, coat the bottom with underbody coating, and coat the top with paint.

I also recommend using masking tape or a piece of cardboard cut to an oval shape, to prevent the underbody coating from covering the surface where the shock mount attaches. That's probably not absolutely necessary, but just seems to me like a neater way to do the job.

Step 12: Install your shock mount and shock, torque to correct specs, and reassemble your carpet and trunk panels as needed. If you look closely at the picture of the top, I also installed a reinforcer ring. I don't plan to do this again any time soon!

Now go drive!