E82 twitchy at freeway speeds- help diagnosing

[roninsoldier83]

I recently picked up an E82 128i that I intend on turning into a track/time attack car (NASA TT5). The car was pretty inexpensive, but I'm trying to sort out getting the car to drive straight and performing deferred maintenance first, before I start with the mods. I'm running into an issue where the car is extremely twitchy at highway speeds.

A bit of history about the car: it was previously in an accident. Based on the photos, it looked like one of the previous owners slid into a wall, damaging the right rear side. Whoever did the body work fixing it, actually did a pretty good job, as the car now appears to be in good condition. Before I bought it, I put it up on a lift and looked over the rear subframe- I didn't see any damage, but I also didn't break out the ruler and start measuring anything either, I just did a visual inspection.

Current condition: I noticed that the right rear side of the car seems to sit approximately 1/2" lower (if that?) than the left rear side. Both sides appear to have OEM springs. I'm not sure if the right rear control arms/knuckle/spindle were replaced (I have a used set of control arms I'll swap on soon), but I didn't see any of them that were noticeably bent (admittedly I didn't measure them). The only aftermarket components I see on the car are a set of adjustable rear toe arms. I'm assuming that after the accident, the toe arms were helpful in getting the toe within spec, either that or it used to be on lowered suspension.

I was lazy right after picking up the car and due to the extreme twitchy-ness of the car, I just took it to a local shop for a quick OEM alignment. In hindsight, I probably should have broken out the string and ruler and did it myself (I'll rectify that soon). When I took it, I could have sworn I saw visual toe-out in the rear. Yet, when they put it on the rack, it came back as being toe-in (positive). I called afterwards (I should have inquired while I was there) and they confirmed, all 4 corners were toe-in/positive. I'll likely confirm this in my garage with some string and ruler this weekend. In regards to the alignment, I can visually see there's more room for adjustment on the adjustable toe arms- I suspect they didn't want to touch anything that wasn't factory. I also suspect I can likely remedy this in the future. There also appears to be a bit of feathering on the inside of both rear tires.

In the meantime, I'm trying to figure out why this thing feels so twitchy at freeway speeds. If the car is showing toe-in at all 4 corners, from past experience, I would think it should be harder to turn, not easier. I'm wondering if there's something I'm missing? Before I start throwing money away that isn't necessary, I figured I would ask you folks to see if there's maybe another area I should be looking into? Maybe I'm on the wrong track to begin with? Or maybe I'm on the right track? Ball-joints? Tie-rods? Power-steering/steering rack? Tires? What areas should I be looking into first?

I'll post the alignment I received and a photo of what the car looked like before it was repaired for reference.

Any thoughts and experiences would be greatly appreciated! Thanks in advance!

[cerealwars]

Hey man, congrats on the new track car!

Seems strange they did not manage to get rear toe in spec, if there was still threads left to go in the adjustment. A few basic suggestions:

Lift the rear end up and inspect it thoroughly. Look closely for cracks in the paint on the subframe, especially near the mounting ears for each arm. Check your shocks for leaks too while you're at it. I bought my car a few weeks ago at 110k and just discovered the right rear is blown out.

Give each tire a real good shake. Any movement? Do this with the car on the ground as well, by giving the top of each tire a good nudge with your foot.

With a helper, grab a tape measure and try to measure rear toe. Going straight across the front of the tire won't be possible due to the driveshaft/etc., but measure as high up as you can. Then try to measure at the same height up the tire in the back. I like to use the straightest, centermost bead for measurement, if your tire has one of those.

Since you mentioned having abnormal rear tire wear, you could try also swapping tires front to rear to see if that changes how it feels. Or if you have a spare pair, throw those on. Weirdly worn tires can cause some strange behavior (pulling, drifting).

[roninsoldier83]

So, I wanted to come back and update this thread in the event someone else runs into this issue. I solved the problem: it was a faulty steering rack and pinion.

It took me a while to be able to articulate the problem to a greater degree, which I failed to do in my initial post. I discovered that the car would wander on the road, to the point where it was borderline terrifying to drive. The car was seemingly unresponsive immediately off of center and would make a noise as though something was loose if you shook the wheel back and forth quickly (at a stop). While shaking the wheel back and forth at a stop, there seemed to be a massive deadspot in the center of the wheel. Because of this, if I turned the wheel just a hair, the car wouldn't seemingly do anything, which required me to turn it further; to which, when it responded, it would turn far more sharply than I anticipated, making it very difficult to keep the car in it's lane, feeling extremely darty to say the least.

I replaced the control arms with 1M/M3 control arms as I plan on tracking it anyway and the car has 133k miles on it, so I figured even if this wasn't my problem, the bushings could use replacing anyway. One of the right rear control arm bushings was in fact shot, with a disconcerting amount of play, but replacing it didn't seem to have much of an effect on the car. I also replaced the rear right camber arm (lower spring perch) and trailing arm with used arms in the event they were even slightly bent from the accident... no change.

I also replaced the right rear hub for the same reason (in the event there was some slight bend from the accident that I couldn't see)- which, didn't solve my problem, but it DID turn me onto another problem: I discovered the right rear axle was damaged, so I replaced it while I was in there. Again, no change.

After hearing the noise when turning the steering wheel, I was convinced the problem had nothing to do with the rear of the car (you can only hear it if you're turning the wheel back and forth quickly while at a stop or very low speed). I got underneath the car with a mechanics stethoscope and had my son turn the wheel back and forth... the noise was loudest on the rack and pinion, right where it's connected to the steering shaft.

I tried tightening the bolt on the rack to see if that would help... all that did was cause a creaking/resistance when turning the wheel and decrease self-centering. I don't recommend anyone try to "solve" this problem with this method, but I tried it out just as an experiment.

I also found a previous thread talking about the steering shaft bolt(s) coming loose, so I tried tightening them. The top bolt was ever so slightly loose, but the bottom bolt was tight. Either way, no change in driving behavior.

I then replaced the steering rack and pinion and while I was in there, I figured I would replace the steering shaft as well (good Lord, that steering shaft is expensive!), along with new hardware/bolts... the problem was IMMEDIATELY solved. Even with the car out of alignment, taking it for a quick test drive, it felt like an entirely different car and the wandering/dartiness was completely gone.

I took the car back to my garage and did a string alignment, rather than paying some grease monkey who was too lazy to touch the adjustable rear toe arms... I was able to get the rear right toe into spec with just a few turns of the toe arms... imagine that. It was a stark reminder as to why I typically never pay anyone to work on my cars and would rather just do it myself to ensure it's done right, or at least if it's not, the only person I have to blame is myself.

I took the car to a different shop just to verify my string alignment was all good and the toe is bang on! On an unrelated note: those 1M/M3 front control arms added almost a full degree of negative camber to the front of the car!

The car now drives great- straight as an arrow! All wandering/dartiness is completely gone and she is now a blast to drive! The rear subframe looks fine, as did the control arms/hub and appeared to have nothing to do with the issue.

I will likely replace the rear subframe anyway at some point, just because it was in an accident previously, just in case. I figure I'm going to drop it anyway to upgrade to stiffer rear subframe bushings, a 3.73 rear diff and LSD, so I might as well just pickup a used subframe from a car that hasn't been in a rear end accident while I'm at it. I'll likely pick up a used subframe and swap new upgraded bushings and the new (used) diff into it prior to dropping my stock subframe, just to break up the job a bit and help it go smoother.

I figured I would pass this along in the event someone ran into a similar issue in the future.