Rear End Swaying Under Acceleration

Hey guys. I've done some searching and I’m going to check a couple of things tomorrow after work but I wanted to post here to see if anyone might have some advice. Up until last week my car was running the factory 18” wheels with 305/35 555R’s in the rear with Eibach Pro Kit springs, BMR Adjustable Panhard and Adjustable LCA’s with relocation brackets. My brackets are set on the lowest (most aggressive) mounting hole on the bracket and are adjusted to what I believe is evenly in length (im going to double check this).


Just this week ive put on my new 20” Vossen wheels with 275/35 fronts and 305/35 rears and centered my panhard perfectly over the rear. When I accelerate hard in second it feels like the car is swaying in the rear. Im trying to replicate it however I can to try and see when it does it. It almost feels like the body is moving over the rear axle. Im running 35psi in my fronts and 30psi in my rears. I had 275’s on front before I switched, so I know it isn’t tramlining the road.


Is it possible that because ive gone to a bigger wheel that I might have not felt the swaying before on my 18” wheels? The car was aligned after all of my suspension work was done. Im going to check my LCA adjustments and try to make sure they are adjusted properly. Any advice? FWIW, it seems to sway to the drivers side.

Did you check to make sure the body is still centered over the axle? Might be time to up grade to a Watts link.

Yea it's still centered. Is it possible that one of my LCA's might be shorter or longer than the other one? And when accelerating the driveshaft would be shifting the rear end around because the LCA's are not equal length?


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How wide is the wheel. Some folks have experienced something like this putting too wide a tire on a too narrow wheel

10.5" rears with 305's. 9" fronts with 275's


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Have you tried lowering your rear tire pressure?

Bushings still good in the LCAs?

Lowering it more than 30psi? I've checked the pressures and they're both equal at 30. So they're not uneven.

The LCAs only have about 3k miles on them so I'd like to think the bushings are still good. I'd be pretty taken back if they're shot. Haha


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Would my alignment have anything to do with the swaying? Thinking about taking the car to have the alignment checked


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Didn't you have to add a wheel spacer to those new rims? Maybe that changed the geometry?

I've had lca bushings go with less than 3k miles before.
Sounds like something is loose, or bent. I would check all bushings, check torque on all bolts and wheel lugs and make sure the relocation brackets still look ok.

hRnYg0aTw33d said:

Yea it's still centered. Is it possible that one of my LCA's might be shorter or longer than the other one? And when accelerating the driveshaft would be shifting the rear end around because the LCA's are not equal length?


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That is a possibility, but I think you would've been feeling it all along. Your car would be crab-walking down the road, and you'd have to have your steering wheel canted in the opposite direction just to go straight. But yeah, your thrust angle could be off.

Also keep in mind that the panhard bar doesn't actually keep the rear of the car from shifting over the axle as the body moves up and down. A Watts link will keep the body locked dead over the axle. If you have the funds, I HIGHLY recommend you upgrade. I used to have an adjustable panhard bar, and I loved it. Then I upgraded to the Watts link and wished I had done it from the beginning.

ShelbyGT5HUN said:

Didn't you have to add a wheel spacer to those new rims? Maybe that changed the geometry?

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The wheel spacer is on the front. But i am not an expert on this so im not 100% sure.

cstunkard said:

I've had lca bushings go with less than 3k miles before.
Sounds like something is loose, or bent. I would check all bushings, check torque on all bolts and wheel lugs and make sure the relocation brackets still look ok.

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I wasnt able to get under the car yesterday, so she sits in the garage until i can. definitely dont want to be driving it in case something is seriously off or in danger of failing.

GT Premi said:

That is a possibility, but I think you would've been feeling it all along. Your car would be crab-walking down the road, and you'd have to have your steering wheel canted in the opposite direction just to go straight. But yeah, your thrust angle could be off.

Also keep in mind that the panhard bar doesn't actually keep the rear of the car from shifting over the axle as the body moves up and down. A Watts link will keep the body locked dead over the axle. If you have the funds, I HIGHLY recommend you upgrade. I used to have an adjustable panhard bar, and I loved it. Then I upgraded to the Watts link and wished I had done it from the beginning.

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Yea im not really sure if i wouldnt have felt it before because of my factory wheels? I wish i could upgrade to a Watts link but its just not in the cards for me at the moment. Have a bachelor party and wedding coming up that ill need to cover at the end of the summer.

Brake rotor retaining clips still on?

^^^^^^^ those MUST come off if you run a non Ford wheel.

all rotor retainer clips have been removed

HillbillyHotRod said:

Brake rotor retaining clips still on?

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That would only cause some crazy vibration, not sway.

im just thinking that if my thrust angle is out of whack...and i go to accelerate hard, the driveshaft would be almost (for the lack of a better term) pushing or shifting the car into or out of position to try and compensate for the unevenness? am i wrong in thinking that? i still have the stock 2 piece driveshaft.

im still running the factory UCA which could be a problem as well.

edit: also noticed that it seems the ass end sways to the passenger side, not the drivers side.

What tires are you running in the rear?

They don't happen to be MPSS's are they?

NT555R's