[e39] lack of directional stability

I posted about this issue before, but still haven't been able to resolve this. The car in question is an '02 530i with sport pkg, 36k miles. Since
I got it at 30k miles, it has not been very solid/surefooted at speeds of 85mph and above. It feels floaty, like I'm getting hit by crosswinds on a calm day and the whole car slightly sways to either side. I have to keep correcting with the steering wheel to remain in my lane.
I had the alignment done/rechecked twice. All the suspension and steering components were visually inspected by 2 different shops - they all claim everything is intact. I have a new set of tires, but the issue existed on the old tires as well, so I don't think it's a tire issue.
I don't want to take it to a bmw dealer as they'll probably tell me to replace all suspension components and charge me an arm and a leg for it. I don't want to blindly begin replacing component after component either. Isn't there some way out there to properly diagnose what is responsible for such stability issues? While it isn't totally awefull, it still takes away from the "ultimate driving machine" experience. I feel like I'm driving a buick.
Where should I start?
Thanks, Pete
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Sounds a bit like the 730d Sport package I drove the other week. Didn't really know where it wanted to go.
Reason......... 20" wheels and rock solid suspension. total crap ride and directional stability and this was a dealer NEW demo vehicle. Wouldn't buy one ever..................
The same vehicle in standard trim with adj suspension + 20" wheels felt like a boat on soft and still wandered and on "sport" mode (stock springs) bumpy and wander. Not a good package. The 19" wheels are about as big as you want to go if derivability is not to be forfeited.
Now the 530 isn't that much different so the same could apply!
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I have the factory 17s with 235/45 tires. I don't hear any other sport pkg. owners with the same size rims/tires complaining about such issues as I'm experiencing.
Pete
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The suspension is usually under considerable forces and it is sometimes difficult to see if anything is actually worn. You need big crowbars and/or remove everything and inspect them. ....or it's just your shocks :-)
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It's very difficult to tell by the old way of levering as there is so much compliance built in as standard. The common wheel shimmy caused by worn control arm bushes may not show up on a UK MOT where they lever everything looking for play.
--
*Young at heart -- slightly older in other places

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote

Before we start blaming parts, I think we need to determine what the conditions are that the car moves around while driving it. If it is merely following the rain grooves sliced into the freeway lanes, then I don't think anything needs to be done at all. If it is drifting all about the road where there are no rain grooves cut, then we can start looking for worn parts.
Having said that, if the car lives in a moderate climate -- like where I live -- then I doubt the suspension parts are worn out yet, unless the car has jumped a curb or two.
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"Jeff Strickland" wrote

It's doing it on all surfaces, even very smooth asphalt ones.

I'm in south Florida. Since I'm the second owner, I have no way of knowing if the previous owner enjoyed jumping curbs over the 30k miles that he owned it. One thing I do know is that the front driver-side fender was repainted at some point. Again, I don't know the extent of the damage that it incured - whether it was just a scrape or the whole left front wheel took a hit. There are no visible scrapes/gushes on any of the wheels. The previous owner could have gotten a replacement wheel though and I wouldn't know about it.
Pete
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The only time I experience what you are describing (328i E46 sport package) is when my winter tires are mounted - not an issue for you. But have you tried increasing the pressure differential between the front & rear tires?
Tom K.
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Tom K." wrote

Yes, I experimented with various pressures, from 30 all the way up to 45 PSI. It did not seem to make a difference for these stability issues.
Pete
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I think you have problems with some bushings on the front control arms. I do not know what is what under your 5 Series, but worn/damaged bushings become suspect since you advised us of the previous front end damage. You could also have rear end damage if the front end repairs were limited to the fender, but there was related damage to the undercarriage that went unrepaired.
Would you describe the direction changes as sudden -- however slight -- or does the car slowly drift off line. Does it always go the same way, or can it go either way?
I once had a car with what I suspected to be a ball joint issue. I found that I could affect the steering behavior if I made a U-Turn to the opposite side. Normally a u-turn is to the left, but I found that if I made them to the right, the car would not do the thing that caused me grief.
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"Jeff Strickland" wrote

They're sudden, and the car can go either way.
Pete
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Bad/miss-adjusted steering box?
RCE
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Pete wrote:

You have had the alignment checked, right?
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"dizzy" wrote

Yes, twice. Alignment was done on a Hunter machine, following all the BMW recommendations such as having a full tank of gas and car loaded with weights (to simulate driver/passenger weight).
Pete
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I've the same problem and feeling on my recently acquired 320 coupe with 30k on. I took it into a Nationwide to have a quick check and they id'd that the rear bushes on the wishbones were split. I've 17"s on - standard I think. I'm wondering whether to put stiffer poly based powerflex / superflex bushes on or go with the BMW rubber ones. - Any ideas anyone?
I agree that it really distracts from the driving experience - it's more of a challenge!. BMW said that they could have a look at it but they charge about a hundred per hour plus vat, and may need to dis- assemble to fully diagnose. Hmmm. Let me think about it...
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Nationwide don't always know what they're doig but neither do the BMW franchises.
Polybushes will mean you can forget about them but you might get reminded of them with a harsher ride.
I have a 10 year old 740 with 130k miles which hasn't been very well looked after and has a guesswork alignment and I don't get the symptoms of the OP. OK it's not rock steady but it's not scary to drive.
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wrote

I have a 3 Series with the Sports Package and factory M3 17" rims carrying 225/45s, and my car goes straight as an arrow. It is "twitchy" on concrete freeways -- it likes to move around a bit -- but it is following the grooves on the cement when that happens. It is rock steady on smooth asphalt pavement.
My car was delivered with 225/55x15s, and I traded them out for the equivalent tires on 17" rims. The tires made absolutely no difference in the personality of my car. Well, the sidewalls are obviously stiffer, and there is some effect there, but it is negligible. At least it does not bother me.
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"Jeff Strickland" wrote

Yeah, that is how my previous A4 (B5) with 225/45/17 tires behaved, too. I could go upwards of 100 mph and it was rock solid. In this e39 I don't feel nearly as confident at high speeds.
Pete
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