Sway from the rear end during hard acceleration

[Andy13186]

I was occasionally having the rear end sway after a minor dip while under hard acceleration when NA but now that I have a whipple the sway seems to be more severe and happening more often. I am not losing traction the rear end just seems to wag for a bit at full throttle after I hit a minor dip or something. I already have the steeda subframe brace. Its a PP1 car and I am using normal street tires when this happens so I don't think its some type of sidewall flex. Has anyone else experienced this and resolved it? Any advice or suggestions would be appreciated. My only theory at current time if nothing is out of spec is that this may be a characteristic of the torsen differential when it is just doing its job trying to maintain traction, but I really dont know if thats a possibility.

Sponsored

 

[TGYNYY]

BMR cradle bushing lockout kit

 

[shogun32]

BMR cradle bushing lockout kit

better yet replace the entire bushing set with Whiteline (very little NVH) or the harder PU/Delrin (more NVH).

Do the Differential lockouts while you've got the IRS apart. If you don't you're going to break the bolts soon enough.

 

[Norm Peterson]

I was occasionally having the rear end sway after a minor dip while under hard acceleration when NA but now that I have a whipple the sway seems to be more severe and happening more often. I am not losing traction the rear end just seems to wag for a bit at full throttle after I hit a minor dip or something. I already have the steeda subframe brace. Its a PP1 car and I am using normal street tires when this happens so I don't think its some type of sidewall flex.

Always a possibility, depending a lot on what 'general level' of street tire, its size, and the wheel width. All of those can and do affect lateral stiffness.

My only theory at current time if nothing is out of spec is that this may be a characteristic of the torsen differential when it is just doing its job trying to maintain traction, but I really dont know if thats a possibility.

Not sure, but I'm under the impression that for acceleration in a straight line a Torsen wants to keep the wheels turning at the same rpm. Whether that allows torque to the two wheels to vary as instantaneous tire grip varies is a different question that I have no answer for.


Norm

 

[1MeanZ]

Check your rear wheel bearings. If they are loose that could contribute to this condition.

 

[NGOT8R]

You’re going to have to address the weak components in the rear suspension to correct the issue that you’re having. Have a look at the video below to see just how bad the factory setup really is.

 

[NightmareMoon]

With unbraced, unmodified stock rear suspension and correct slight toe in, the car may wag its butt slowly when spinning the rear tires.

if its exessive and hard to control it could be a bad wheel hub. If its minor and controllable then bracing or bushing upgrades in the rear should help.

check the hubs for play, probably check the rear alignment, and then maybe decide if you need additional parts to fix it.

 

[15GTPP]

Get some Viking Crusader Shocks. They helped a bunch with my rear end sway. B358AM is the part number if I remember correctly. I upgraded to the Kelltrac Spec. The Shocks made a night a day difference for me.

 

[offroadkarter]

Check your rear wheel bearings. If they are loose that could contribute to this condition.

This was my problem, my car would dance around really bad under throttle at highway speeds. Turns out the drivers rear wheel hub was very very shot.

 

[KewlWinter]

I notice this issue slowly develop over the course of 6 months of daily driving after purchase. I replaced the rear lower control arm bushings and knuckle bushings with bearings and the vertical links with new links with 1 bearing, 1 delrin bushing. Also put in the cradle alignment bushings and the BMR cradle lockouts. There is NO comparison! Not only did the issue completely go away, the car is so much more planted and responds exactly as expected, whether cruise, acel, or decel. I did not install everything in one go. I did it in phases so I could access the difference at each step.

 

[Andy13186]

Thanks guys.

I ended up ordering pedders adjustable coilovers and the rest of the steeda stop the hop ultimate package (already have the subframe brace), and their aluminum diff bushings. Not sure if I want to do the diff bushings but I think the diff bushings may definitely be contributing to my issue. Also the pp1 suspension definitely isnt made to deal with 750+ rwhp I think there is just too much weight on the rear while full throttle now for the OEM components to sucessfully control it. Also my whole suspension has 40k hard miles on it anyway so its probably due for an overhaul.

 

[Andy13186]

You guys suggesting to check the hubs were right I think.

I was having a clunk noise when I put my car into drive and reverse at a stop that I ended up having diagnosed and repaired before doing any suspension changes. Apparently my rear hub thrust washers were cracked and that damaged both the hubs and axle surfaces. Both hubs were replaced along with both axles and crush washers.

This definitely fixed the noise and I think it significantly reduced the sway on accell after dips, although I am not sure if this even makes sense. I am not sure if I should do the coilovers or not now since it doesnt seem nearly as bad but I am still considering it.

Edit* it still does sway more than I would want so the mods will be done

 

[Bluemustang]

Not sure, but I'm under the impression that for acceleration in a straight line a Torsen wants to keep the wheels turning at the same rpm. Whether that allows torque to the two wheels to vary as instantaneous tire grip varies is a different question that I have no answer for.


Norm

I believe it does. The grip at each tire or lack thereof creates the friction at the gears, which is what allows the diff to apply torque to the other side. And it's essentially instantaneous because unlike a clutch type you don't have to wait for it to load up. The Torsen diff is always working under both acceleration and on decel off throttle.

 

[Bluemustang]

You guys suggesting to check the hubs were right I think.

I was having a clunk noise when I put my car into drive and reverse at a stop that I ended up having diagnosed and repaired before doing any suspension changes. Apparently my rear hub thrust washers were cracked and that damaged both the hubs and axle surfaces. Both hubs were replaced along with both axles and crush washers.

This definitely fixed the noise and I think it significantly reduced the sway on accell after dips, although I am not sure if this even makes sense. I am not sure if I should do the coilovers or not now since it doesnt seem nearly as bad but I am still considering it.

With a Whipple - it'd be a very good idea to upgrade the suspension. Some slightly stiffer springs and better dampers will do wonders. And as others mentioned, the rear cradle lockout kit is pretty important- the rear subframe on these cars shift around quite a lot.

 

[GapSauceInc]

I was occasionally having the rear end sway after a minor dip while under hard acceleration when NA but now that I have a whipple the sway seems to be more severe and happening more often. I am not losing traction the rear end just seems to wag for a bit at full throttle after I hit a minor dip or something. I already have the steeda subframe brace. Its a PP1 car and I am using normal street tires when this happens so I don't think its some type of sidewall flex. Has anyone else experienced this and resolved it? Any advice or suggestions would be appreciated. My only theory at current time if nothing is out of spec is that this may be a characteristic of the torsen differential when it is just doing its job trying to maintain traction, but I really dont know if thats a possibility.

Similar issue, similar setup. What I found was all four swaybar end links were shot. Replaced them and most of it went away. I have most of the bmr parts in rearend already. Last thing is replacing the diff bushings and using the upgraded bolts.

Sponsored