[casualDIYer]

This DIY will cover the install of AC Schnitzer rear lowering springs (Part No. 3130231330) made to be fitted to BMW F30 xDrive chassis (consult AC Schnitzer for part numbers to match your vehicle) along with BMW F80 rear bump stops (31337847662). While it is not a requirement to install different or shorter bump stops with lowering springs, the topic has been often discussed in this community with a noted preference for either cutting existing bump stops or replacing them altogether with shorter models. ACS Schnitzer does not offer bump stops as part of its lowering spring kit. This kit (3130231330) will lower the car roughly 20-25mm. The damper used with these springs on this install are Koni Sports with adjustable rebound. These springs are rated as OE spring replacements. Check with AC Schnitzer for updates on compatibility with OE and aftermarket dampers.

The methods presented on assembly/disassembly are not BMW authorized instructions. It is suggested you verify all measurements and repair techniques with official sources to ensure they are correct for your vehicle. Suggest you consult other DIYs as each DIYer will emphasis aspects of this install they consider important, which is often based on their experience.

Tip: Do this with a friend. Or grow another arm.





Getting Started
You will need to remove the rear struts. If you do not/not plan to replace bump stops, you still need to remove the strut from the car. The strut will get in the way of removing the spring so it has to be removed.

1. Remove rear struts (see https://f30.bimmerpost.com/forums/sh....php?t=1865875 on how to do this). You may do one side at time. During the strut removal, you will need to remove the areo shield under the strut. Notice next to the strut bolt, toward the inside of the car, there is a small rubber nib (part of the bottom spring perch). This acts a guide pin to orient the perch on re-assembly. It is very important to note the fact the guide ‘nib’ is closest to the strut bolt and not the centre of the car. There are two holes the pin can poke out of on the control arm. Do not orient the bottom spring perch over the wrong hole in the control arm during re-assembly.



2. If you are working on the left side of the car (facing the front), with a 10mm socket and 8mm combination wrench disconnect the headlight level sensor arm (attached to the control arm) from the sensor pivot arm (attached to the sensor). Forgetting to do this step could result in the snapping of the sensor arm, the pivot arm, or damage to the sensor. Or, all three. Note the sensor pivot orientation (pointed almost horizontally toward the front of the car)



3. Now you will need to remove the bolt that holds the wheel carrier to the lower control arm. Yes, it’s really held on there at 165Nm of torque, which is a lot. Depending on your available tools, you may need a breaker bar. Depending on your F30, the bolt is either a 21mm hex head bolt or E20 bolt held on with a 21 mm nut. Once you removed the nut jack up the control arm to make it easier to free the bolt.



4. Once the wheel carrier bolt is removed, slowly lower the jack. Once the arm is freed, you will notice the arm will spring backward, the carrier forward. We’ll deal with this in upcoming steps but it’s a huge pain in @ss to deal with later. Welcome to rear toe. To get the spring out you will have to remove the strut (dealt with in step 1). Push down the control arm just enough to pull out the spring. Note: Do not remove the upper metal cup that houses the upper rubber spring perch.



Difference between coil overs and lowering springs? The upper metal cup where the upper spring perch resides. In adjustable coil overs, that cup is replaced with an adjustable perch. Not so with static ride height springs. DO NOT REMOVE IT.



5. With the spring out, you will notice it has a top and bottom rubber perch. This part has got to be easy right? Swap to the new spring? Some subtle but important steps must be taken.

1. The spring needs to be oriented upward. In the ACS case, the company logo and part number are written on the spring. The spring is oriented correctly when the logo/part number are oriented upward.
2. The end of the coil is slotted into a coil stop. It’s critical you orient the perch as shown, top and bottom. Why? As the car drives, the coil can turn in place. Without a stop, the coil will proceed to shred the crap out of perch requiring replacement. Blunderful.
   
   
   

6. With perches back on the coil, the assembly can go back into the car. Remember the guide nib back in step 1. It’s got to back to its original location. Turn the spring so that it does. You may find that as you place the spring back in the control arm, the top perch cup will knock off the top rubber perch. What a pain. Take the spring out, and make sure that top perch coil stop is oriented with the coil end.



7. Wonderful. The most hellish part of this DIY, re-assembly. Which could take up to 50% of the time to complete this DIY. I found that if I reattached the strut to the chassis, then to the control arm, that helped a little with orienting the wheel carrier bolt. Remember, at this stage snug in bolts. Final torque will come later. You will notice that as you use a jack to raise the control arm, the arm is not aligned with the wheel carrier. This is due to the rear toe. I found that as I slowly jacked up the control arm, if I pushed it forward with my foot that would help align the arm with the carrier. Note: Safety shoes are ideal here. Should have bought a pair. As you raise the arm into the carrier, a screw driver can be helped to orient the bolt holes.




TIP: Not shown (but should have, damn!) you can use two jacks. One to raise the wheel carrier and one to raise the arm. A friend really helps here because as one person raise the jack slightly, the other will attempt to orient the bolt.

IMPORTANT: Orientation of the bolts that hold the strut and damper is very important. For example, bolts may be ‘HEAD FIRST’ (the head of the bolt is pointed to the front of the car) plus ‘REAR FIRST’ (head pointed toward rear). Or, REAR + REAR, or whatever was done at the factory. The point here, be sure to identically replicate the bolt orientation.

Once the bolts for both the strut and wheel carrier are snugged, place the rear wheel back on the car, and using a ramp, let the car sit under its own weight. Using the torque while under weight is the technique often illustrated by both Bilstein and Koni. The ramps have to be high enough for you to get under the car to torque the bolts.

The strut bolt to control arm is 100Nm
The wheel carrier to control arm is 165Nm. Yeah, it’s a lot, especially when you’re lying on your back.

DO NOT FORGET
1. To re-attached the headlight sensor on the left side of the car
2. To re-attach the aero shield under the strut

Good luck.

PS: Member Skyhigh (see reply below for his exact text) has posted there is a kit called the BMW "Poor road package" spacers for F3x. This kit is designed to resolve issues with reverse rake with ACS springs, where the rear of the car sags lower than the front. So far, on my F30, I have not had this issue. I don't know the reason why this would happen but the F3x chassis came with multiple engines, including the 6 cylinder B58, N54, and N55 and the 4 cylinder N20 and B48. Not hard to imagine a heavier engine could help a bit in keeping the nose lower than the tail. It should be noted ACS does have part different part numbers related to cars with 4 vs 6 cylinder engines. Verify fitment for your vehicle. I almost bought the wrong set but when I submitted my VIN, the vendor noted the mismatch and sent me the correct set.

[Skyhigh]

Thank you for taking the time to describe this and take photos!!
I am sure it will be very useful to some, although there are youtube videos showing this process, which may be more appealing to others.

One important clarification from me:

Originally Posted by casualDIYer

IMPORTANT: The bolt the holds the strut to the control arm is ‘HEAD FIRST’, in order words, the head of the bolt is pointed to the front of the car. The bolt that holds the wheel carrier to the control arm is ‘REAR FIRST’

This is NOT always the case - it depends on the ModelYear as well as on the continent! My European LCI F36 had both bolts in the same direction and the bolts were NOT the same (at least one of them) as seen in various youtube videos, so different tool bit size was required as well!



(Dual jack application also visible on the photo )

Best advice - pay attention and take note of the bolt head type and orientation before even commencing work and ensure correct tools are available.

Another comment:
The AC Schnitzer springs tend to create a "hang ass" on an appreciable number of our F3x vehicles, depending on the model and configuration (weight). My rear was also nearly 2cm lower than the front, after conversion. This can be (partially) rectified by installing BMW's "Poor road package" spacers for F3x, which lift the rear back up with 8mm.

I did that post-factum and this gave me a much more harmonic look of the car. It no longer looked like I have bags of rocks in my trunk when it was in reality empty. Details can be found in other threads.

[casualDIYer]

Originally Posted by Skyhigh

Thank you for taking the time to describe this and take photos!!
I am sure it will be very useful to some, although there are youtube videos showing this process, which may be more appealing to others.

One important clarification from me:

This is NOT always the case - it depends on the ModelYear as well as on the continent! My European LCI F36 had both bolts in the same direction and the bolts were NOT the same (at least one of them) as seen in various youtube videos, so different tool bit size was required as well!



Best advice - pay attention and take note of the bolt head type and orientation before even commencing work and ensure correct tools are available.

Another comment:
The AC Schnitzer springs tend to create a "hanging ass" on an appreciable number of our F3x vehicles, depending on the model and configuration (weight). My rear was also nearly 2cm lower than the front, after conversion. This can be (partially) rectified by installing BMW's "Poor road package" spacers for F3x, which lift the rear back up with 8mm.

I did that post-factum and this gave me a much more harmonic look of the car. It no longer looked like I have bags of rocks in my trunk when it was in reality empty. Details can be found in other threads.

Thanks for the info. I've updated the DIY to reflect bolt orientation should be identical to the way BMW installed the bolts on the car.

As for the ACS Springs, I did come across a few users concerned about what is called 'reverse rake' (i.e. ass hang), where the car leans back, not forward. It's definitely a top concern for those looking for lowering springs. So far I have not encountered an issue with the F30 but it's good to know there is a solution if it comes up. I've added to the bottom of the DIY for those it does effect.

[Skyhigh]

Well done!

And just to illustrate the reverse rake as i experienced it...:



I believe it is pretty obvious. The car is empty on this photo, although it looks like I just picked up someone from the airport

This is with AC Schnitzer front and back, no spacers.

[casualDIYer]

Originally Posted by Skyhigh

Well done!

And just to illustrate the reverse rake as i experienced it...:



I believe it is pretty obvious. The car is empty on this photo, although it looks like I just picked up someone from the airport

This is with AC Schnitzer front and back, no spacers.

What a pain in the ass to deal with. That kit from BMW fixed it to your liking?

[Skyhigh]

You mean "what a hang in the ass to deal with"? )

It did, much more balanced look, very glad I installed the spacers.
The remaining reverse rake is negligible and typical for BMW. Can be seen on stock M3s and M4s too.