Secondary steering in left turns, Mazda3, I'm out of ideas.

I'm trying to solve an issue with my Girlfriends Mazda3 and am totally out of ideas, so this is obviously the best place to turn.

07 Mazda3, 182k miles, owned since now, now fairly heavily modified but all bolt on (2.5 and 6 speed swap, Konis, Eibach springs, MS3/MZ5 brakes, RX8 18" wheels).

When taking fairly gentle but higher speed left turns, the car turns twice. Basically, once you get a little bit of load on the right side suspension, the car then rotates more than the initial steering input, and then takes a set at that new point. Once you unload the suspension, you can feel it shift back. This is only on left turns, and is really only noticeable at higher speeds. There is no extra movement in the steering wheel when this happens.

To me it seemed like a bad bushing in the rear suspension that was deflecting causing dynamic toe change under lateral load. I've replaced:
-Both rear trailing arm bushings (at the front of the trailing arm, part 2 below) with hardrace bushings
-Both lateral links with new OEM bushings (part 3 below)
-Both upper rear control arms (part 7 below), with adjustable parts to reduce the negative camber for better tire wear
-Rear shocks have less than 20k miles
-Both lower control arms (part 8 below) with OEM bushings. That's all of the bushings in the rear.

Other things checked: -The rear wheel bearings have no play in any direction and made no strange noises.
-The tires are nearly new, This has happened with two different sets of wheels and tires
-Rear subframe has been dropped and then re-torqued
-Alignment is within 1/16" by my tape measure when adjusted tonight after finishing the LCA swap.

I've also checked out the front for good measure, and the only things not perfect is some very slight slop in the steering as the pinion goes from one gear on the rack to the next tooth, which feels like every other car, and some very slight binding/tightness in the strut top bearings but they have no play.

Here is what the rear suspension looks like:

I'm totally out of ideas on what else to try. Does anyone have any thoughts of what to check next?

My ms3 used to do that to me all the time. A big fat swaybar and new endlinks took care of it. The other possibilty that i can see is sidewall rollover due to a defective tire.

Is it possible that the steering rack mounting is loose on the right side?

Or maybe a strut going bad. I have a similar problem with the KYB's on the duster.

I've had this happen when a sway bar bushing went bad.

Whats up with your bump stops? Are they stock or cut down to accommodate the lowering springs?

Most Eibach stuff is fairly low-rate, I think.

My theory, and I am just guessing here- Car turns in, weight transfers, the load shifts onto the bump stops, causing the spring rate to immediately rise. You don't notice it as much on the right turns, because the suspension is a bit pre-loaded by the weight of the driver and the contact with the bump stops isn't as abrupt.

If I'm onto something at all, you could play with rebound damping on the Konis (crank it to full stiff) and see if that slows down the weight transfer enough to soften the landing, so to speak. If that's the case, the real fix will be stiffer springs. Dunno, just guessing here.

^ bump stops can easily be checked to see if they're being hit by putting a dab of grease on em. If it gets bumped you'll see a grease stamp.

In reply to Sonic:

Do you feel the rear step out at all when it happens?

Pete: it doesn't step out like oversteer feeling, you turn the wheel, the suspension gets a little load, then the car turns more while the steering wheel does not move. When the load comes off of the suspension, it is fine again.

Swaybar bushings: those are cheap and easy to change, I'll try that

Bump stops: they are original and I modified, and the small amount of load needed to cause this likely isn't getting them involved, but it is only three bolts to take off the shock/bump stop combo that I'll swap them left to right and see if there is a change.

Shocks are nearly new in the rear, but when I swap them left to right we will see if the symptom follows the shock.

Tires are also nearly new, and this has happened with both the summer and winter sets.

Steering rack: possible. I've pried on it and don't see any movement, and the steering wheel does not move at all when this all happens...ill try the other rear things before I get to this.

Thanks for the suggestions so far!

If you don't feel it in the steering wheel, I think you're looking in the right direction at the rear suspension. I would have recommended checking the upper front strut bearings, but sounds like you've already done that. Failed strut bushing could possibly do it, but would almost definitely also cause a leak. I have seen ball joints with the spring-loaded lash cup that are totally worn out but don't feel like they have play until the suspension is loaded, and then the cup pops back and lets the ball move around. They usually clunk though, and at least in my non-power steering cars, you can feel it though the wheel.

The 1g cars were sort of notorious for the step out you describe. I always figured it was snap over. But i wemt full coilovers and hotchkis sways at the first sign of trouble, so theres that.

It was fine for 180k miles, so there must be a reasonable way to fix it...ill see what happens from the side to side shock/bump stop swap then the swaybar bushings.

Can you tell me more about the 2.5 swap? I have a 04 with a possible need for a newer engine due to excessive blow by.

I also wonder if you might have sway bar bushing bind in the front? Like the bushings are loading up in a turn, then suddenly releasing their stuck bind, causing more roll, and therefore more tuck in and turn?

The only time I had that problem was with a rear wheel drive. I had to move the rear axle forward on the rear leaf springs to make a short drive shaft work. One of the U-bolts worked loose and the axle would move back and forth turning the car. Because it was rear wheel drive it happened under accel/decel also. I would check the rear trailing arms for loose bolts or bad bushings.

4Msfam wrote: Can you tell me more about the 2.5 swap? I have a 04 with a possible need for a newer engine due to excessive blow by. I also wonder if you might have sway bar bushing bind in the front? Like the bushings are loading up in a turn, then suddenly releasing their stuck bind, causing more roll, and therefore more tuck in and turn?

The 2.5 swap was pretty easy for my car, but I think it might be harder for yours as the 04-05 cars were significantly different from the 06 up, though at this moment I don't remember the differences. For our 07, the 2.5 swap was basically a long block swap with an intake manifold adapter plate. We are running the stock ECU with the 2.5 injectors. We scored a 900 mile 2.5 from a 2012 Ford Fusion locally for $700. From there we had to swap everything over from the old motor...oil pan and pickup, valve cover, wiring harness, accessory drives, manifolds. The intake manifold was the only difficult part, as the ports in the head on the 2.5 are huge, and the 2.3 manifold did not seal well with them due to the size difference, so we used an adapter plate to fit between them that let them seal up well and it has been fine since. The 2.5 has significantly more torque than the 2.3 did. The 6 speed swap was just as easy, it was from a 2010 Mazda3s. It literally bolted up exactly in place of the 5 speed using the mounts from the 5 speed.

Only the insane would consider an engine block and transmission swap a bolt-on. I mean that in a good way.

It's not likely to be the same thing, but: The trash can Civic had very similar sounding (but probably much scarier) handling when I got it and it turned out the inner tie rod ends were worn. It was bad enough on that car that the wheels could be moved a fair amount when they were off the ground, but maybe yours are just going down that road?