Rear End Shifts on Accel/Decel

[White64Goat]

Been a long time since I posted here.......have a 2013 BRZ and recently I have noticed when driving the car and accelerating up through the gears that when I shift and let off the gas and then get back on the gas, the rear end is changing directions. Can also make it do the same thing by hitting and letting off the gas. Have visually looked at the rear bushings and don't see anything wrong by the eye. Wondering if anyone else has had this problem and what it was?
Thanks.

[Ohio Enthusiast]

I'd check all drivetrain bushings - rear subframe, diff mounts, transmission and shifter mounts and engine mounts. All of these contribute to the rear being squarely.
In addition, check your suspension links, especially toe arms. Make sure everything is tight, bushings are in good shape and toe isn't out of whack (slipping or loose toe adjuster, for example).

[ZDan]

What are your tire pressures? What you describe is how a Torsen diff behaves when you have rear tires of different diameter, or one is at lower pressure.

[strat61caster]

I’ve also seen this when cross weight is jacked, ignore if on non adjustable spring perches.

[grippgoat]

I'd check wheel bearings and axle nuts, too.

[Muskoka800]

Originally Posted by ZDan

What are your tire pressures? What you describe is how a Torsen diff behaves when you have rear tires of different diameter, or one is at lower pressure.

I experienced this. My right rear tire was worn significantly more than the left. The rear of the car stepped right during hard accelleration. No effect noticed during braking however.

[White64Goat]

Tire pressures were the first thing I checked and all were good. Wear is even on all tires as well. Car is also puling to the right as well and it has driven straight as an arrow since I've had it. As far as I know there has been no curb contact to knock alignment out of whack. Going to take it to the dealer next week probably as driving it out on the interstate it has a constant tug to the right which is annoying as hell.

[JohnH]

Originally Posted by White64Goat

Tire pressures were the first thing I checked and all were good. Wear is even on all tires as well. Car is also puling to the right as well and it has driven straight as an arrow since I've had it. As far as I know there has been no curb contact to knock alignment out of whack. Going to take it to the dealer next week probably as driving it out on the interstate it has a constant tug to the right which is annoying as hell.

something is loose, broken, worn significantly, or both/all 3. I'd take it to see a known good professional who knows these cars or similar types of cars, not just "the dealer" unless your specific dealer has a guy who really knows what he is doing, and the service manager allows him to work that way, not just typical dealership flat rate. I am a professional tech and have worked at dealerships in the past. Just my advice.

[ZDan]

Originally Posted by White64Goat

Tire pressures were the first thing I checked and all were good. Wear is even on all tires as well. Car is also puling to the right as well and it has driven straight as an arrow since I've had it. As far as I know there has been no curb contact to knock alignment out of whack. Going to take it to the dealer next week probably as driving it out on the interstate it has a constant tug to the right which is annoying as hell.

You might confirm which way the car zigs when on the gas, and which way it zags when off the gas, and then swap the rear tires left/right and see if it behaves the same way or the opposite (i.e. zig on gas becomes zag on gas). If behavior flips, perhaps a bad tire with internal defect like delamination or some such...

[White64Goat]

Installed 4 new tires and the issue went away. Didn't think the tires were all that bad but when I jacked the car up and spun them, boy were they not in good shape. So, issue solved.