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The rear end of my car dances in all directions when hitting a bump or takes a load such as hitting slush/snow.
The problem appears to be in the rear sub frame, the bushings are shot where it connects the submframe to the chassis and this causes lateral (horizontal movement) which allows the tires to move in a left/right direction under load.

Here's a video displaying the movement:



I'm wondering -- has anyone swapped out a rear subframe before? Can i just puchase replacement bushings and swap them out and keep the existing sub frame?

I highlighted the items that need replacing, i would be looking at doing all 4 if this is possible.
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My 2004 FX45 was "dancing" too, but I did not replace my rear subframe bushings because mine looked in decent shape. The problem is that over 15 years the rubber gets hard, but if your bushings are deteriorated then sure. Give it a go an let us know how you made out.

I would first replace your rear shocks and shock-rubber bumper pads. These too get hard, but I think your bounce is caused by an old shock that gets "stiffer" with every rapidly occurring bump in the road. Note: My mechanic told me my rear shocks were fine, because they are not leaking, but after I replaced them my car road smoother.

My bounce/dance is much, much better now, but I replaced my steering rack bushings ($40) and I replaced my front and rear sway bar bushing, and all sway bar links, which is not that expensive and easy to do.

You can read about this here: Think Your FX35/45 Suspension Is Too Tight (Hard)...

My mechanic was right when he said: Every little bit helps!

Further, my FX45 has 20" wheels and low profile tires (265/50R20). However, I went with a Michelin Primacy XL tires (255/55R20) which are 1/2" taller and 3/8" narrower than the OEM tire. Why? ...My goal was to achieve a "softer" and "lighter" feel on the road… and I got that.

Plus, I was able to order these tires on Amazon (delivered) for only $170/tire! ...But you will have to find a local (non-big-box store) to put these tires on your car. Or Costco will sell these Michelin’s at $225/tire since this tire is within 3% of OEM specs, but they will not guarantee it, because this size is not matched in their system for your FX.

If I were to do all my repairs over, my other desire would be to turn this performance FX, that sometimes rides like a truck, into a luxury sedan. That said, I wish I could find a pair of rear shocks and/or front struts that were specified for an Infiniti or Nissan touring sedan (???) …and I would slap these parts in my FX45. Why? ...Because I don't want to fight the road bumps anymore and I don't care if I lose handling performance if I got in exchange a luxury car ride!

My FX45 rides like it did off the showroom floor, but since Infiniti designed this FX suspension "stiff" out of the factory, it will never ride like a luxury sedan; unless… you can find a softer shock and strut specified for an Infiniti or Nissan touring sedan that will fit your FX. But where to find these?

If anyone goes this route, please let us know how your ride changes?

Note: Polyurethane bushings are harder than rubber, so I would not go this route, if you are looking for a "softer" ride. Also, I don't know of the G35 or G37 suspensions ride softer, but I would investigate this model struts and shocks to see if the "footprint" is the same as your FX model. Likewise, you might look at the newer QX models if your research shows Infiniti made both shocks and struts that are not as stiff vs. our FX models?

Good luck, and please keep us updated on how you went about fixing your "road dance."
 
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