Still having stability issues

OptionZero

Longer explanation:

All of the suspension components work together and affect alignment. Changing one may, and likely will, affect the entire suspension. Think of a pyramid, and if you change the length of one edge you affect the entire shape. This is why people like me tell you to get the damn SPL Catalog - full adjustability to get your alignment perfectly dialed in to what you want

SPL has come out with a buncha options so explaining this is going to be harder than before.

Generic diagram of rear 370Z suspension. The focus is on arms number 11, 12, and 14.


#14 is the arm that has a bucket for the spring.
What you replace it with depends on whether you have true type or OEM type rear coilovers. The OEM type has the spring separate from the shock. The spring sits literally in the bucket, hence the name, and the shock is bolted to other connection points.

OEM type coilovers require this:
Rear Adjustable Toe Midlinks for the 370Z and G37 | SPL Parts
Look at the pix and it is obvious why, it has a bucket for the spring. This affects toe and also height since it provides adjustability for how the spring sits.

True type requires EITHER:
Adjustable Rear Toe Arms for the Nissan 370Z and Infiniti G37 | SPL Parts
or
Adjustable Rear Toe Arms for the Nissan 370Z and Infiniti G37 | SPL Parts

SPL just happens to have two designs now, apparently.

Arm #11 is the camber arm
It is replaced by this:
Adjustable Rear Camber Arms for 370Z and G37 | SPL Parts
or
Adjustable Billet Rear Camber Links for the 370Z and G37 | SPL Parts

Again, SPL has a regular and billet version. As the name states this controls camber

Arm #12 is the traction arm. it affects toe and is replaced by this:
Adjustable Rear Traction Arms for the 370Z and G37 | SPL Parts
Looks like just one version is sold now

lastly, you need this:
Eccentric Lockout Kit for the 370Z & G37 | SPL Parts
From the factory, toe adjusted with an eccentric bolt that is prone to slipping. Since you have all adjustable arms, you no longer need this adjustment point, and it's just a weakpoint for alignment to be disrupted anyways. The lockout kit is just like the name - it locks this bolt in place so it does not slip, leaving your alignment intact from your other arms

This problem is not the Z - the problem is you didn't think this thru from the beginning and learn what it takes to lower a Z and what it takes to get the alignment properly adjusted

This is why we all tell you to do much more reading before doing anything

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