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CoolATIGuy CoolATIGuy is offline
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Car: 2007 BMW 335i E90 Sedan (N54) Manual
Question Fighting with Steering - any Guesses?? - 07-21-2021, 09:23 PM

2007 BMW 335i, N54, E90 Sedan, Manual Transmission, Sport Package with Oil Cooler

- ctless downpips
- Upgraded Chargepipe with BOV
- Upgraded 5" FMIC

~180k miles on the clock. JB4 with Bluetooth kit and MHD backend flash.

In the past, I've felt confident at higher speeds, even with more aggressive maneuvers. However, now the car feels unsettled, particularly above 50 mph (especially at 65-70+), and primarily when turning the wheel, in either direction - more aggressively makes a larger impact. For example, when switching lanes on the interstate moderately quickly, or when taking a sweeping curve at higher speeds, when the wheel is allowed to come back to center, it feels like it tries to "overcorrect" itself almost the same distance in the opposite direction, before quickly returning to center. You can feel the wheels moving back underneath you and the car is unsettled.

If you turn the wheel quickly 45 degrees to switch lanes for example, then try to bring the wheel back to center after changing lanes, the wheel will kick back in the opposite direction with almost the same intensity, before quickly coming back to center and leveling out.

The car tracks fairly straight, and doesn't seem to get too unsettled when just driving straight, unless at higher speeds and then hitting a road imperfection or somesuch. It seems like when the front starts to go one direction, it starts getting some boat/floaty action in the wheels back and forth, then settles down again. I've done a fairly straight pull before to higher speeds and it did start to get squirrelly and I had to back off, even though there wasn't a lane change or curve, probably just grade change/road imperfections.

I did take it in to have it looked at by a different euro performance shop than my normal shop, and was told the suspension looked good and tight, but the rear toe arms had been installed backwards...I had those turned around, and the car seemed to handle great again. So I figured it must have been related to that. But, when I had the rear tires replaced just a few weeks ago, as soon as I left the tire shop, it immediately was back to feeling wonky. All they did was jack up the car slightly and replace the rear tires.. So I took it back to the euro performance shop to have an alignment done (although I was not confident that would fix the issue - it's not a static tracking issue, it is a dynamic issue that happens when the car's trajectory is changed), and before they aligned it they checked it out again - now are saying my rear subframe bushings should be replaced along with the differential mount bushings..

The rear subframe bushings being worn seem to possibly make some sense (although I'm not sure why those weren't noticed/mentioned before if that is true) - maybe turning the rear toe arms around moved/resettled the worn bushings a bit to give it some temporary relief, and then maybe jacking up the car to replace the rear tires jostled it back into it's inevitable worn position? Although, it doesn't "feel" like it is the rear end that is moving/sliding around when all this happens - it feels like it is the front/steering fighting back/countersteering before straightening up. But, if it is something in the front, I don't know why it would have gone away and then come back when only the rear was really messed with. And I know the rear can push/affect the front.

There are no squeaks, rattles, bangs, no noises that would seem to give something specific away, either at low speed or high. The suspension in general feels very solid and tight, the steering does not seem to have a lot of play or anything, and at lower speeds like <30-40 mph it seems to handle normally. No issues turning into parking lots or anything like that. But I have felt the car when it is performing as expected at higher speeds, and it inspires substantial confidence. That confidence is pretty much all gone now.

It has a Bilstein B12 Pro-Kit (which is Bilstein B8 struts in front, Bilstein B8 shocks in rear, and Eibach lowering springs on all 4 corners). The rear shocks are less than 2 years old. Around a year ago I also had the front drivers side and passenger side inner and outer tie rods replaced (both front tie rod assemblies), replaced rear drivers side and passenger side track rod track struts, and replaced rear drivers side and passenger side rear track arm bolts with eccentric cam adjusters with replacement used ones that were in better shape, all done by my indy/tuner 335i specialty shop (they specialize in N54/N55). I also just put new tires on the back a few weeks ago.

18" wheels, don't have runflat tires

Spending $1000 in labor and a couple hundred more on rear subframe bushings and diff mounts just to see if that's the problem or not, is a pretty expensive trial process. My normal shop (again, that specialize in 335i), didn't agree with the other euro shop that suggested rear subframe bushings; they said they rarely see those requiring replacement even at high mileage and seem to want to point me back to upgrading the shocks/struts to something different, which I really don't think is the issue. It's felt planted and solid with my setup before, I'm not thinking different shocks/struts are the answer here.
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Default 07-22-2021, 10:17 PM

Rack and pinion would be my guess.
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CoolATIGuy CoolATIGuy is offline
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Car: 2007 BMW 335i E90 Sedan (N54) Manual
Default 07-23-2021, 09:52 PM

Thanks for the reply!

So, a couple pieces of info after some additional testing:

- The steering does not feel extra firm, or extra vague, or shake or have extra play, or have trouble returning to center (after it counter pulls/pushes to the opposite side), doesn't make any odd noises, no grinding or rattles or creaks or clunks or anything odd as far as sounds or feel through the wheel, even the actual turning of the wheel to initiate the lane change or enter the curve is fine and seems normal - the issue is just when the wheel is trying to return back to center (especially during medium aggressive manuevers)

- The issue occurs in both directions, left and right; possibly slightly more to the right, but that could just be in my head. It is probably safe to say it is close to 50/50 in terms of issue turning left vs right

- The issue is virtually unnoticeable below 50mph. Between 50-65 is where you start to feel it. It starts to feel extra sketchy above 85.

- There does not seem to be extra body roll

- INTERESTING AND POSSIBLY MOST HELPFUL?: I did realize that the issue is not as pronounced during acceleration; when letting off the throttle however and coasting, allowing the weight to move over the front suspension more and not quite as much over the back, the issue is much more obvious and aggressive. I'm not sure if this is more indicative of a possible problem in the rear or the front though...just that it seems to noticeably affected by deceleration vs acceleration. It also does it while braking. For example, an evasive maneuver such as braking while turning to go around an object or vehicle to avoid a sudden collision is a somewhat risky affair as it overcorrects back to the other way.
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