[casualDIYer]

Another DIY for dampers but this time for Koni’s Yellow Sports (Koni 8240, Part Num: 1294SPORT) for a 2017 340i xDrive. The Yellow Sport shock part number may vary for your F30/31 so check with Koni for exact fitment. These dampers can be characterized as having slightly firmer compression, adjustable rebound, and compatibility with factory springs, even for non-M sport suspension equipped cars (such as mine). This DIY covers the rear shocks only. The prime goal is to test changes to suspension dynamics of the vehicle as components are swapped. So far

Swap chassis-side front thrust arm bushings to monoballs (Millway Street)
- Slight improvement in steering response
- Less front end dive during moderate to heavy braking
- Slight increase in NVH

Camber Plates (Millway Street)
- Better preservation of tire shoulders at high speeds
- Understeer reduced
- Set at 2 degrees, at near max steering input, slight oversteer noticed.
- Slight increase in NVH

Rear damper swap (Koni Yellow Sport) – Set to ½ turn from fastest (i.e. loosest) rebound
- A slight increase in chassis stiffness is felt.

Getting Started
It is far easier to pre-set the rebound before installation. In fact, you should practise setting it over and over so you understand how it works. You cannot set the compression of the shock, only rebound. The best material describing the rebound adjustment process is found on YouTube by Koni itself

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In the written instructions (which I would describe as needing improvement)) included with the damper Koni shows a vice to clamp holding the threaded rod while turning the shock body. I don’t think this is great technique due to the possibility of destroying a thread or two of the rod. A purpose-built tool would better. In fact, in Koni’s video it appears the Koni rep has such a tool. I'd pay $20 for it.

My observations in setting the Koni Sport shock rebound setting:

• I encountered a comment that recommended the rebound not/not be set to either its max or min setting but to any setting between one half turn from max or min. This is to avoid the detent becoming engaged when the rod is fully compressed into the body.
• When depressing the threaded rod to lock in the detent before turning the shock body, I found using a 5mm hex key, with the long part wrapped in a micro fibre cloth, easiest.
• Do not bother trying to figure out how many turns you are away from fastest (i.e. loosest) rebound or slowest (i.e. stiffest) rebound by ‘eyeballing it’ (i.e. watching how fast the rod returns to its top position). Engage the detent, and turn the body, carefully, to max speed (loosest setting), then count turns from there. Pushing the rod in and watching it pop out seems to me an inaccurate way to gauge settings. The damper is built to handle the weight of 400 kgs of car and resist a giant metal spring, also designed to hold up 400 kgs of car. Even a heafty human is not going to accurately simulate the car.
• Rest the shock body on a non-marring surface, like a soft carpet or cloth, when making adjustments. Scratches can expose the steel which can then start to rust. If you scratch the damper, a little car touch up paint post install, can help stave off rust.
• The top of the shock body has two recessed holes opposite each other. I added two pieces of tape 90 degrees from the holes to help determine how many turns I had made when adjusting the shock.
• I added a label to tell me which way the body need to be rotated to make the rebound loser (i.e. faster).

Aside (skip if you just want the DIY)

Fastest = Loosest = Least Stiff
Try this, take a new shock out of the box (or set it to it's loosest setting), turn it so the thread rod is pointed toward the floor. With the rod held against a non-marring surface, lean on the body pushing it to its max travel. Flip the shock body so the rod side up and gently pull the threaded rod upward. There is some resistance. Now, set the shock to ‘max’ and try again. It’s very hard to pull the thread rod back to its original position. When the shock is set to max stiffness, you see the rod react slowly. When the shock is set to min stiffness, it reacts quickly.

Setting your Konis depends on where they will be used and the springs used with them. In general, city streets, have lower tolerances for smoothness and undulation. Dampers need to react quickly to avoid tire skipping, where the strut and spring are compressed, but the decompress rate (i.e. rebound) is so slow, as the tire clears the bump, the road falls away faster than the tire can follow. In essence, the tire is briefly airborne. This momentary loss of road contact affects both steering and braking. In searching for settings for various BMW sedan chassis (E46s, E90s and F30s), settings from ½ (very common) to 1 full turn (track day settings) from loosest (i.e. fastest) were the most frequently encountered. I’ve been testing ½ turn from quickest and all is fine but it seems a little soft for me. May try 2/3 from full soft next.

End Aside

Note: There a lot great videos on how to swap dampers. Suggest you watch a few, especially board member Farkle’s video, who has been a prolific contributor to the F30/31 DIYer crowd here on this site.

1. Get the car up on jack stands. You can jack up the rear of the car from the differential. Note, do not jack the differential up by the seam, nor its rear cover, but on the body of the differential.



2. Remove the rear wheels and the underbody/areo shield that protects the bottom of the shock. Now remove the 3 E12 shock mount bolts. I found using an extension makes it easier to access and remove the bolts.

3. Once the E12 bolts are removed, remove the 18mm strut-control arm bolt. Using an impact gun and long 18mm socket (a short socket may make it difficult to get the impact gun in place), undo the nut, while using an 18mm wrench to hold the head. Note the orientation of the bolt—head first (i.e. pointed to the front of the car). It must be re-fastened in the same orientation. Hold on to the shock body and pull out the bolt. Once free, you may have to compress the damper a bit to remove it.



4. Once free, you will have to remove the damper vapour cap, which is pressure fit to the damper. I used a nylon prise tool. What about a screw driver? With plastic/nylon parts be wary of using metal tools to remove them. When new, nylon is pliable. As it ages, it can crack. As the cap is there to prevent rust, if it cracks, arrange to get an new one.



5. Using a pass-through wrench and 16mm pass-through socket, along with 5mm hex key to hold the threaded rod, remove the 16mm shock bolt. Do not/not use an impact tool as that may damage the internals of the damper. I know you saw "a guy" do it somewhere, but literally every set of instructions I've seen from 4 different damper makers is clear. No impact tools should be used to remove or reattach the nut from/to the threaded rod to avoid damage to damper internals. Plus, the 'exotic' pass-through wrench is cheaper than a new damper.



6. <Unique to Koni> Before adding the shock mount to your new Koni shock, be sure to include the shock body protection disk to avoid premature damper failure if the body comes into contact with the bump stop.
Reassembly order: Shock body (obviously) + white protection disk (not obvious but necessary for Koni) + bump stop (very bad to forget this, so don't) + shock mount + nut + gasket + nut protector



7. <Unique to Koni> Place the shock mount on the top of the threaded rod, along with the paper gasket, and use Koni’s 17mm nyloc nut to attach the mount to the shock. Note that BMW uses a 16mm nut, but Koni uses a 17mm nut, which fits. Koni has a guide for torque values that based on size of the threaded rod (M10) and the type of fastener (nyloc). In this case, the value is 45 Nm (33 ft lbs).





Note: Nyloc nuts have a limited life. While not single use, they lose locking ability with each use. Since BMW uses an M10 flange bolt, that can be used in place of the nyloc bolt. Or, you can use a nut with spring washer. Koni’s torque guide covers all these variations

8. If you compare the two shocks, you will see the Koni has a longer rod than BMW which misleads you into thinking that Koni’s rod is too long. This is not an issue. Also note the nylon vapour cap is a tight pressure fit. You may have to use a little lubricant to help fit it back into the shock mount or a tiny little bit of sanding of the mount with fine grit sanding paper. Critically, make sure the cap if fully aligned as it goes back on the damper. As the mount is screwed back onto the chassis, it will push the cap into the mount.



9. With the shock and mount assembled, it’s ready to go back into the car. I found it easier to mount the shock to the chassis first. There is a nylon guide pin that fits in a hole in the chassis. Take care to not break the pin. Also, note that the vapour barrier may get curled. It must lie flat when the mount is placed back into the chassis. Once the mount is in, you should be able to hand thread the three E12 bolts then continue with a ratchet. The torque of these 3 bolts is 28Nm.



10. Once firmly attached to the chassis, you will notice the shock body does not perfectly align with the control arm-strut bolt hole. Use a jack to slightly lift the control arm then use a screw driver to align the bolt hole. Place the bolt (head first = toward front) back in the hole and refasten the 18mm bolt. Suggest using a long socket. Do not torque to the final value yet.



11. The final torque value of the control arm bolt is 100 Nm but it needs to be torqued with the car resting on its wheels. Koni tells you the suspension must be loaded before the control arm bolt is torqued. With the wheels on, I lowered the car onto ramps, and torqued the bolt to its final value. At this point you are now done and can re-attach the underbody shield.