When your friend sends you a clip that looks like this, you pack your car full of tools and drive straight to the parts store to pick up two new springs. Ideally while laughing at your friend for not noticing the problem for potentially hundreds of miles of driving. This type of failure on what otherwise looks like a fairly new spring is pretty uncommon, but for the mileage on this car – around 100,000 – it’s about time to replace them anyway.
BMW, in their infinite wisdom, put the top of the strut mount under the rear parcel shelf speaker, so you’ll need to pop up the trim, use a T25 to remove the three screws holding the speaker in, then pull up the foam covering the mount. Once you do that, you’ll find the three 13mm nuts holding it in place, so you can remove those, then use a 21mm socket to remove the rather large single bolt holding the shock to the hub. Once that’s out, you’ll need to pry the shock out as it has a half moon socket it sits into the hub with.
To get the shock out, you’ll likely want to remove the rear trailing arm. It’s one nut and one 18mm bolt, although we ended up snapping the shaft of the ball joint clean off so I’d suggest just taking the rear bolt out and swinging the arm out the way instead. Still, the shock should be able to slide out towards the rear of the car.
Once it’s out, it’s time to defuse the bomb that is the string. Attach a spring compressor set and tighten it all down until the spring is loose from the top and bottom spring seats. Once it is, either use a special socket that will let you undo the nut while using an allen key to hold the shaft still, or just use an impact gun to spin the nut off. Remember to carefully remove the spring compressors from the old spring.
At this point it’s worth inspecting your old shocks. We did. It didn’t go well. Push the shaft all the way in, it should be smooth and should steadily rebound itself to full length, relatively quickly. We are not talking mountain bike shock quickly, but like 30 seconds. The original one took something like 5 minutes to return to normal. So we took another trip to the parts shop and picked up two new shocks. We also got new lower spring seats because the old ones look wrecked.
Now if you are just replacing the spring, you should have it easy. Place the spring back on your old shock and make sure it’s fully seated on the spring seat. Place the top mount back on, again in the right orientation, then use the spring compressor to squeeze the spring down enough to put the nut back on the top. If you are using new shocks, you’ll need to align the new spring seat so the spring sits correctly and the lower shock mount lines up with the hole it needs to sit into. We messed this part up twice, getting it close enough to right on the third try. The top mount’s studs are an isosceles triangle with the furthest point being almost directly in the middle towards the front of the car.
Once you have the strut together again, you’ll then need to fit it back on the car. This bit sucks. Getting the top mount in really requires two people and is a massive pain as you can’t see anything either way. I have no tips for you here except suffer as we have. Twice. For a single shock. Yeah. As for the lower bolt, that’s not much better. Assuming your lower control arm bushings have been set correctly – which ours weren’t, check out the video in the cards to find out why… – you’ll need someone to stand on the brake calliper and or disc to push the hub down far enough to get the lower mount in and bolted. In our case we ended up needing to loosen the lower control arm bolts to be able to flex the knuckle low enough, then we got it in. We of course also replaced that broken trailing arm too.