[lucysparabola]

Hi,

car is a 2013 535i. Took in under SilverRock (lol) warranty before it expired (came with the car, I didn't pay for extra) to address destroyed shocks/springs/mounts/bushings. after a war, they OK'd the fixes.

They tried to give me KYB shocks, which I laughed at, so instead I bought the Bilsten B12 Pro kit from RockAuto and had that delivered to the shop.

new shock mounts and new bump stops were put on as well. The B12 for the F10 does require all four bumps after speaking at length with Bilstein on this one. it wasn't the case on my E60, but is for the F10.

The rear sags lower than the front does, still. B12 kit states all four springs are the same height. The car had this issue prior to the replacements being put in, so it makes me think something else is up.

the other alarming part was, when the B12 kit was done - under heavy accel, the rear of the car would wrench back and forth as if it were going to come apart. Took it back to the shop, they discovered that the rear subframe had been replaced recently prior to me owning the car and the bolts were not torqued to spec. They fixed this and the danger of the wrenching is now gone. The car was downright dangerous for the 24h I had it after the B12 kit before we caught this.

But, it still crashes hard over some bumps, particularly at high speed - and that rear right side knock is ever present. Every other bolt was checked in the rear by the shop after the subframe debacle, so, I am confident that there isn't anything else loose there.

Can anyone shed some light here? I'm ready to drive the car off of a cliff quite honestly. Shop manager who worked on my car is also at a loss. He has an F10 550i himself with EDC, his doesn't sag at all in this manner. He's going to do some digging around as well this next week until he's back in town, but, my god this has been a nightmare. I am at the point where I hate the car now.

damping has improved no doubt, but this rear knock & crash over some bumps has to be fixed. otherwise I'll sell the car in a month or two tops. my other choice is to get the KW DDC kit, which I probably should have done in the first place - but there has to be something else we're missing for it to sag like this.

rear sags lower than the front, and right rear sags more than left rear.

thanks.

[MeekM535i]

Hi,

you should check or better replace the 4 rear subframe mounts that are attach to the chassis and possibly the diff mounts too. I'm pretty sure that they are the cause of the problem. I would recommend you to insert PU (polyurethane) instead of standard rubber mounts, thus you will solve the "looseness" of the rear subframe. The car will be much more manageable and predictable in critical situations, as well as a lot more firm over bumps, in fast curves as well as during wheel slippage.
I did it on the previous e90,just replaced it with standard rubber mounts, the difference was like night and day. For example, in a corner especially at some high speeds, the rear subframe ran away and was very unpredictable especially when there were some bends / holes , then you had the feeling that the whole rear end was "swimming" but without the wheels slipping. And when we talk about the fact that the surface is wet and the rear wheels start to slip and getting some grip, it feels like the car is going to fall apart. After the replacement, it was drastically better, so that even on bad roads and all this condition it was much more stable.
I currently have the same problem with the F10, I also replaced the worn shock absorbers with a b12 kit. As you say, the damping has been improved without a doubt, but the rear end behaves like my previous e90. I will soon replace those worn-out subframe mounts for PU (despite the fact that these mounts on my subframe don't visually look bad at the moment, without some cracks, wear and tear... it can still be felt when driving, especially when other things have been repaired, in this case shock absorbers and similar)

As for the knocking in the rear left end, I'm not sure what it could be, maybe a wishbone or a balljoint that has been knocked out, but it might be hard to see what it is.

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I hope you will solve the problem or maybe you have already solved it?

[lucysparabola]

So the rear subframe bolts were not torqued properly, as it seems to have been replaced recently prior to me buying the car. the bolts were torqued and not loose to the hand, but they were loose to the wrench. so, my shop torqued them correctly and that fixed the slippery issue 100%.

Issues that still remain are the crashing on some bumps / road gaps in the front and back (the back is definitely worse) as well as the rear right knocking over said bumps / gaps. I am 90% sure the right rear issue is a control arm bushing that is gone.

Did you replace spring pads/shims with your B12 kit? My car's stock suspension apparently never had them, or did not have them at the time of replacement and the shop didn't realize they needed to be added back in. so they're waiting to be installed as well when shop has an opening. insanity... i know.

I fear the ride harshness may just be a function of the B12 kit. I might have to go to B4s and stock springs, or go full stupid and get the KW EDC retrofit kit. I just want my cruiser to be comfortable!

thank you for the detailed response.

[3002 tii]

Sorry not very helpful but should you decide to switch, I can vouch for the Dinan springs. I’m running those with oe m sport shocks and car handles great, no jarring ride and overall stance is tad lower than factory.