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Discussion Starter · #1 ·
I'm the original owner and have had an annoying issue with this car since day one which nobody seems to be able to solve. At highway speed in a mild constant radius right curve I accelerate (in 5 th) and the car pushes left. When I release throttle, the car comes back right. It will take about 100 yards for the car to completely change lanes at around 60 mph. A left curve does not produce any problem. However if I'm in a similar left curve, an yank up on the hand brake the car will push right. I've checked and triple checked all the rear suspension components including the subframe and found no cracks. BMW did a four point wheel alignment and everything is within spec. except for the rear axle "geom. driving axis" which has target data of 0 degrees 30 minutes +- 13 minutes and the measurement is 46 minutes. From the name of the spec it sounds like it's the angle of the rear axle to the chassis, but then why wouldn't it have a target point of 0 degrees? After a test drive with the shop foreman they're explaining it away as a result of soft bushings in the rear control arms in combination with engine torque. Sounds a bit fishy to me. Any ideas at this point would be welcome. Oh, one more thing, the car has never been raced. Kind of a shame but I'm a bit of an old fart.
 

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It's rear steer from the soft stock subframe bushings. The entire subframe rotates in the horizontal plane for this reason. While cornering, on the throttle the outside wheel will be toed in. Lift throttle or brake or hit some bumps and it'll toe out. Makes for increased tendency for snap oversteer too. Replace the stock subframe bushings with the Ireland green subframe bushings. It will cure the problem and you'll be a much happier camper.

Thrust angle spec is 0 degrees +/- 15 minutes. The number they quoted you is the total toe spec, not thrust angle.
 

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Discussion Starter · #3 ·
Daniel,
Your explanation sounds good - thanks. For the life of me though, I can't understand why it does it in right curves and not left. The only asymmetrical force would be from the engine. Could that cause that much difference in rear toe? One more thing - is it possible to change the subframe bushings without dropping the exhaust and rear end? Again thanks.
 

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Daniel,
Your explanation sounds good - thanks. For the life of me though, I can't understand why it does it in right curves and not left. The only asymmetrical force would be from the engine. Could that cause that much difference in rear toe? One more thing - is it possible to change the subframe bushings without dropping the exhaust and rear end? Again thanks.
I suspect you're just not noticing it as much in left turns due to sitting on the left side of the car. Back when I replaced my stock subframe bushings with the Irelands, it looked like the stock right side bushing was deflecting more than the left side bushing (judging by how much paint had been rubbed off of the subframe support brackets). Which makes some sense given that the one other mounting point is to the left (differential cover ear). But that would lead to the opposite of your conclusion (worse when turning left). How much do you weigh? :)

If you search here you'll find a lot of chatter about the Ireland subframe bushings. I'd call them required for all Z3 cars. Yes the exhaust has to come out and the subframe has to be lowered. Also need a tool to get the stock subframe bushings out. But it's far and away the most significant handling improvement you can make to these cars. The bushings are cheap, but the labor isn't unless you can do it yourself.
 

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Discussion Starter · #5 ·
I'm 185 lbs. The same scenario occurred when I went for a test drive with the BMW shop foreman and I'd estimate he weighed 150 lbs. I'm going to improvise some force deflection tests and see what I come up with. I don't mind changing the bushings because the rear does feel a bit sloppy - always has. But I don't want to go through all that and find that the problem persists. I'll post again when I have some results. Thanks again.
 

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Not trying to rain on your parade, but this is an old subject resolved years ago. Unfortunately, the rear end is basically all over the place with the stock subframe bushings. I realize you're new here, but do a search for 'subframe bushings' and you'll find more information than you need. A thread I started in Feb. 2005 on driving impressions wouldn't be a bad start:

http://www.bimmerfest.com/forums/showthread.php?t=60613
 

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Stevewz, I had exactly the same feeling as you when I first got the car. Any throttle modulation in high speed corners was just so unpredicable and would really upset the car.

IE bushings made things feel so much more connected.
 
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