severe sway at track

[thundr306]

Went to the track two weeks ago and trapped 130mph, straight as an arrow. 2011 GT, 6a, Magnuson, stock rear suspension.

This past Saturday, I downloaded a new tune trying to improve my shift rpms/firmness. Nothing else changed from two weeks ago. The tires/rims never even got changed.

My first pass, the car went .2 faster than two weeks ago. There was a very small amount of wheel hop at launch (1.6 60'). Before half track they car started swaying, I stayed in it and they swaying got really bad by the finish line. At the time slip shack, I was told the tower called and told me I had to figure out what was wrong with my car or they were going to kick me out for safety. I doubled checked all lugs and tires pressures. I didn't see anything bent underneath, so I upped my tire pressure by 2lbs to 20lbs just because I was trying anything.

Pass two...launched with a lot of wheel hop and by half track it was swaying so bad that I lifted and rolled through the lights.. They basically told me that was it for the day as they didn't want an accident at speed.

I drove the car home almost two hours without an issue. Also, I had a high speed run, but not high load run on the way home without any sway issues.

Could the stock control arms be deflecting under load, even at that speed, enough to make it sway that bad? Any other ideas?

Thanks

 

[Bossmustang16]

that what sucks about slicks.. I cut 1.5 60 ft's with a radial with just lowering springs and upper arm and mount. and never sways at all drives like a street tire.. You should invest in some mickey thompson radial pro's... best tire out. slick tread with radial sidewall and radial drivability

 

[2011/5.0]

Surprised your running stock control arms at your power level. You really need to upgrade lca and uca that will take care of some of the hop. You may have torn one of the stock bushings

 

[thundr306]

that what sucks about slicks.. I cut 1.5 60 ft's with a radial with just lowering springs and upper arm and mount. and never sways at all drives like a street tire.. You should invest in some mickey thompson radial pro's... best tire out. slick tread with radial sidewall and radial drivability

I ran 130mph two weeks earlier without any issue, so who knows.

Surprised your running stock control arms at your power level. You really need to upgrade lca and uca that will take care of some of the hop. You may have torn one of the stock bushings

Looks like I am going to do some Black Friday shopping for some suspension parts. I'm guessing a bushing too.

 

[JEWC_Motorsports]

What tires are you on, front and rear?

 

[thundr306]

What tires are you on, front and rear?

28x4.5-17 m&h racemaster
295/55r15 goodyear eagle ss drag radial

 

[JEWC_Motorsports]

Sway can come from multiple things, mixing radials with bias ply tires is one of those things. Get your suspension in order and you will know if its from the tires.

 

[thundr306]

Sway can come from multiple things, mixing radials with bias ply tires is one of those things. Get your suspension in order and you will know if its from the tires.

I am going to get some rear suspension. I dont think its the tires as ive been running these up to 130mph at the track. It felt like tire sway but 100x worse.

 

[JEWC_Motorsports]

Have you looked at your lcas and diff bushing?

 

[konablue11gt]

with all the wheel hop you described are you sure you don't have a slight twist in your axel tubes?

 

[retfr8flyr]

+1 Check for an axle tube problem or a crushed stock control arm bushing. That much sway shouldn't be from the tires.

 

[thundr306]

Thanks for all the tips. I should have some time today to take a good look at it. I didnt see anything from a quick look.

 

[Sharad]

Control arm bushings will do that, but I would check tires, then rear end, then bushings.

 

[drive_55_not]

The only time(s) I've had bad swaying with my car is when I drop the tire pressures to 12psi. The rear starts wondering pretty good past the 1/8 mile and I look like I'm steering a boat thru the trap..

The LCA bushings could be torn however since the sway is that bad I'd surmise it's a tire issue, the sidewall could've broken down.

The pumpkin bushing was ripped on my car and I had no noticeable handling effects from it but I have aftermarket LCA's..

.

 

[thundr306]

Looks like I am pulling the rear axle assembly and taking it to a local chassis shop to get checked out.

 

[thundr306]

Housing and axles both checked out ok.

 

[psfracer]

I first thought bushings when I read that--especially since you said it was the same tire/wheel set up vs 2 weeks prior when there was no problem.

As long as you verified the air pressure was in fact correct.

 

[BMR Tech]

Since your axle checked out okay, you now need to get the car on an alignment rack. If you have any issues - it will show on the rack/screen.

If the alignment looks good, it is likely a ripped bushing or 3.

The stock diff bushing and UCA bushing in these cars is very prone to prematurely failing, but.....at this point, I would recommend just doing the entire thing. UCA/Mount....LCA...and a good diff bushing or bearing.

Keep us updated. I'm interested in seeing what your thrust angle is hen you get the alignment checked.

 

[thundr306]

Thanks for all the suggestions/help so far.

No rips in any of the bushings, but they are awfully soft.

I did place a big suspension order through AM on Black Friday, but everything is still on backorder.

Any suggestions on a diff bushing? I don't want a spherical bearing.

I did some research on the drag radials I am running and have read some stories of people with the same issues. They had severe sway as soon as they installed them.

 

[psfracer]

Any updates on this one? Curious of what you found. Like I said earlier, as long as the air pressure was around 15-18 psi in the DR--and they are the same ones you used the 2 weeks prior with no sway--I think its still something in the rear suspension.