I hit a big pot hole and heard a crunch near passenger rear deck. It turns out my top shock mount failed and the shock poked through into the rear deck plastics including damage to deck, speaker, and trim.
I changed the rear shocks 10K miles ago to Bilsteins H6 (spec'd for 540i). I think I must have done something wrong upon install.
Pic of shock poking through rear deck top mount:
Pic of normal deck top mount (driver side):
Pic of shock removed:
Pic of shock top mount closeup:
Below is OEM parts diagram. I removed #5 cup support and #6 shock absorber bumper since bilsteins have built in bumper. Was that my mistake?
When I installed the shocks, I removed #6 support cup and #5 shock absorber bumper since bilsteins have built in bumper. Was that my mistake? Any help would be appreciated.
you definitely want to check that those Bilstein have internal bumpstops... pretty sure they do not.
If they don't have the bumpstop, the shock compressed fully, maybe even beyond its designed range, and that's how it punched out the rubber mount. :eek
Internal bumpstop shock vs. No-Internal bumpstop shock:
you're referring to the rubber/foam pad inside the strut mount. Since the OP used the OE springs, he does not need the 540i part. That part is only necessary for smaller diameter springs, usually on coilovers.
I cant answer if not including those parts were contributing factor but thats some heavy structural support there. For it to have done what you stated and pushed through to me thats sounds more like mount failure as it was rusted and compromised and failed. I also am unable to see pics but could be due to work restrictions on images. Look at the other side see if there are any signs of fatigue.
Is it possible the rubber bushing was installed in that top hat backwards? I would have expected the larger diameter lip of the bushing to be on the bottom side towards the shock body, to better resist displacement from compression forces.
The rear upper shock mount comes from the manufacturer with the rubber busing already pressed-in. From the picture, it looks like the rubber busing was in the correct orientation. Without the bump stop in-place, it must have been the shock body hit the rubber busing so hard that it pushed it out of the upper mount metal housing.
The bilstein rear b8s don't come with internal bump stops?!??!?!
I just put the thing together as well!!!
But also if they do, I'm.pretty certain you should RE-use the top part of the bump stop the big cup spreads the load from the shock over the whole surface of the top mount centre shaft.
Seems to me the bottoming out issue caused the mount to push through. The interesting piece is that the stocks springs, even compressed fully, should allow enough travel so that this doesn't happen.
I know that when I did my Dinan and Koni set up the rears required a bump stop from the 540i IFRC. So it would seem correct that a OEM bump stop for the rear would be needed. I realize that you are using Bistein and could be different.
Thanks for the input. I purchased the shocks from Tire Rack. I am hoping to get some answers from Bilsteins through the Tire Rack guys. I am also going to order the bump stop and support cup.
How did you like the new shocks before their rude entrance? Thinking about getting a set of the same. Also very curious to hear what failed so I don't have the same fate.
From the discription of the incident, and the lack of bumpstops, nothing failed. The shocks where missing a critical component, and the pothole was big enough to compund the damage. The suspension couldnt compensate for the pothole without the bumpstop. So the energy transfer took out the next softest parts, the top mount, and the rear shelf.
In retrospect, I think I would have gone with coilovers to lower the car slightly and get some adjustability. I love the lowered M5 look. Ride height with current setup is pretty close to stock oem height. Ride is firm but handles well. I would say the overall ride is 7/10. Of course I am an old fart so take that into consideration. I just ordered bump and support cup along with new top mount.
Sorry for your troubles, and I really have nothing substantive to contribute, but I will say that it is encouraging to see the shock mount tore before the rear deck. At least you have no structural damage to the rear deck.
Sorry to see this OP. As others mentioned, at least this failed with minimal collateral damage.
Do BC coilovers need anything extra in the rear to prevent this?
I have placed order for cup supports and bump stops. Hopefully, back on the road within a week. Thanks for everyone's input.
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