Under heavy braking the rear end feels like it sways left and right like its loose

Unde accel it pulls left and decel pulls right

I've read a lot about the tire pressure problem but its even. I've tried 2 different rear rims and the same effect

I am about to check subframe bolts.

Any other suggestions?

I've done both rear wheel bearings and check all suspension bolts

Alignment has been done twice by a reputable shop and suspension is near new eibach r2

Tires are hankook rs3. Rear toe arms are Megan

 

Could be a combo of worn out dampers and crumby soft side walled tires. Too much suspension moment in braking/dive will cause the rear to unload and toe out, accelerating does the opposite, throw some crumby tires on there and it could be the icing on the cake. Whats your alignment spec? Maybe thats f@#ked up.

 

Updated more setup info. Double it's any of the stuff you mentioned

 

I would start looking at the front suspension components...
does the steering feel off when its doing it?

 

A friend had an interesting issue where the welds that held the offsetting plate for the front inner lower control arm bolt broke free allowing the bolt to squirm. Before he repaired it he told me about how unpredictable and loose the car felt and then after what a relief it was. Maybe it's worth a look?

 

Replaced front compliance bushing and checked the settings and bolts. Under braking the front feels solid just the rear shimmy s. ill be checking on Friday and was looking for a check list

 

MIne did this when I had RC5+ front and back so the bias was messed up. heavy braking would cause the back to shimmy. Guessing it was the bias, but now with XP 10 F and XP 8 R problem solved.

 

When you tried different rims, was that with different tires as well?

Any time you get weird left/right pulling symptoms like this and pressures are equal, swap the tires left/right and see if the problem changes direction. Could have a bad one...

 

How many miles on the car and how many miles on the Megan toe links? Could be worn bushings.

 

Bushings have 10k max. I am about to swap rears to try. Also when I tried new wheels they were same tires