My car is trying to kill me!

[sgale]

Hey All,
long time reader, first time posting. I've recently done a handful of suspension modifications the the IRS in my 2016 GT PP, and have had some weird behavior that I'm hoping to get some input on.

TL;DR: my car is trying to kill me by wanting to rotate when lifting off the throttle at highway speeds

Mods: the car has SVE lowering springs, Steeda IRS braces and Steeda IRS bushing kit, SVE 19x9.5 with Michelin pilot sport 4s 274/40/19 square

Problem: when cruising on the highway in 5th or 6th, when i lift off the throttle (light to moderate acceleration) the front pulls left and the rear feels like its pushing right, give a feeling of the car wanting to rotate about the center to the left. I notice it pretty consistently and its a very unnerving feeling when just driving to work. I also take a sweeping left turn on a daily basis and the back end feels like its shifting and then takes a set. On real wet roads I'm concerned that I'm going to loose traction and spin out.

With all of that being said, I did recently get a couple session in at Mid-Ohio and found that the car didn't really exhibit these handling characteristics under high loads. I initially had a traction problem, but I attributed that to new tires needing to be heat cycled for the first session. the second session I had a lot more grip, but had some brake fade that kept me from going over 7/10ths. So I'm not sure I got a good read on the cars real performance capability.

The parts I've installed were intended to improve handling, and all the reviews of the parts say they should, but I'm not seeing that in real life. I've had the car aligned twice. The first time the car was very twitchy on the highway. The second time i requested a more stable straight line set up at speed, and I got that. But now the car feels almost loose when turning.

Alignment specs are:

Front:
LH
Camber -2.2
Caster 7.4
Toe -0.04
RH
Camber -2.2
Caster 7.5
Toe -0.04

Rear:
LH
Camber -1.7
Toe +0.13
RH
Camber -1.7
Toe +0.13

Total Toe +0.26
Thrust angle 0.00


Any suggestions or help would be really appreciated. I'm not sure what to do to make the car livable again.

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[BmacIL]

Hey All,
long time reader, first time posting. I've recently done a handful of suspension modifications the the IRS in my 2016 GT PP, and have had some weird behavior that I'm hoping to get some input on.

TL;DR: my car is trying to kill me by wanting to rotate when lifting off the throttle at highway speeds

Mods: the car has SVE lowering springs, Steeda IRS braces and Steeda IRS bushing kit, SVE 19x9.5 with Michelin pilot sport 4s 274/40/19 square

Problem: when cruising on the highway in 5th or 6th, when i lift off the throttle (light to moderate acceleration) the front pulls left and the rear feels like its pushing right, give a feeling of the car wanting to rotate about the center to the left. I notice it pretty consistently and its a very unnerving feeling when just driving to work. I also take a sweeping left turn on a daily basis and the back end feels like its shifting and then takes a set. On real wet roads I'm concerned that I'm going to loose traction and spin out.

With all of that being said, I did recently get a couple session in at Mid-Ohio and found that the car didn't really exhibit these handling characteristics under high loads. I initially had a traction problem, but I attributed that to new tires needing to be heat cycled for the first session. the second session I had a lot more grip, but had some brake fade that kept me from going over 7/10ths. So I'm not sure I got a good read on the cars real performance capability.

The parts I've installed were intended to improve handling, and all the reviews of the parts say they should, but I'm not seeing that in real life. I've had the car aligned twice. The first time the car was very twitchy on the highway. The second time i requested a more stable straight line set up at speed, and I got that. But now the car feels almost loose when turning.

Alignment specs are:

Front:
LH
Camber -2.2
Caster 7.4
Toe -0.04
RH
Camber -2.2
Caster 7.5
Toe -0.04

Rear:
LH
Camber -1.7
Toe +0.13
RH
Camber -1.7
Toe +0.13

Total Toe +0.26
Thrust angle 0.00


Any suggestions or help would be really appreciated. I'm not sure what to do to make the car livable again.

If the rear toe and camber are accurate, a definite source of your problem lies with your 0.10 deg of toe out. Toe out makes the car much more twitchy at speed. Toe in does the opposite. I'd go for right on 0.00 or just a hair of toe in. With your camber settings and tires, the car should not feel that oversteery in corners, it should feel very nice, but I don't know what the spring rates of those SVE springs are. I'm guessing they didn't have anywhere near the time spent on development like BMR and Steeda have put into theirs.

Do you just have the Steeda alignment bushings or do you have the subframe support system? Since you've already got the braces, investing in that would be a good idea. That locks the rear cradle from moving around like crazy.

 

[sgale]

BmacIL so the car with that current alignment doesn't feel twitchy like it did with the first alignment. the toe in the rear for the first alignment was -0.15 each side for a total of -0.30. That was one of the adjustments that happened to give more stability at high speeds, and the car is very stable in a straight line under load.

I also had the same question about spring rates with those SVE springs. according to LMR they are FR: 200-314 in/lbs and RR: 800-914 in/lbs. which isnt a giant departure from the BMR handling spring. At least on the surface.

The steeda parts I have installed are: 555-5754 - Steeda IRS Subframe Support Braces, and 555-4437 - Steeda IRS Subframe Bushing Support System so I think that's what you are referring to.

hopefully this helps clear some things up about my situation.

 

[sgale]

update from LMR:

a customer care rep has had the same issue and says that while the rear suspension is loaded to loosen and re tighten the control arm bolts and all suspension hardware. He says this has corrected what he suspected to be a bind somewhere in his IRS and fixed his problem.


does this right? Anyone with some experience in this department? and what constitutes "all the suspension hardware"

Thanks!

 

[BmacIL]

BmacIL so the car with that current alignment doesn't feel twitchy like it did with the first alignment. the toe in the rear for the first alignment was -0.15 each side for a total of -0.30. That was one of the adjustments that happened to give more stability at high speeds, and the car is very stable in a straight line under load.

I also had the same question about spring rates with those SVE springs. according to LMR they are FR: 200-314 in/lbs and RR: 800-914 in/lbs. which isnt a giant departure from the BMR handling spring. At least on the surface.

The steeda parts I have installed are: 555-5754 - Steeda IRS Subframe Support Braces, and 555-4437 - Steeda IRS Subframe Bushing Support System so I think that's what you are referring to.

hopefully this helps clear some things up about my situation.

They are copies of the Eibach Pro Kit, based on that. 200/800 are the actual rates of the springs. The 314/914 are with the bump stops.

The LMR comment about clocking the bushings is accurate. This is something you need to do on a 4-post lift or alignment rack.

 

[Monopoly]

I had a very similar issue while back on my Dodge Stealth. Turned out the front upper strut nuts came loose. Took me forever to figure it out.

Maybe try tightening everything up to torque specs? Just a thought.

 

[NightmareMoon]

I had a very similar issue while back on my Dodge Stealth. Turned out the front upper strut nuts came loose. Took me forever to figure it out.

Maybe try tightening everything up to torque specs? Just a thought.

Yup, thats my guess. Strut nut may have come off, and/or you have a failing wheel hub.

When my GT started pulling different directions under acceleration versus braking, it was a missing strut nut. Very bad news and squrirelly handling under power too. I noticed a clunking sound in addition to the car pulling to the side under braking. My steering wheel would be ~5 degrees different to hold the car straight under power versus braking.

To check the hubs, jack up the corner and try to push/pull on the top/bottom of the wheel and see if there is any shifting, noise, or movement. That might also work for the front struts, but a visual inspection with the front wheel off should also be done to check for strut bolts.

FWIW, I am experimenting with some toe out, and currently have 3x more toe out than the OP (-0.15 degrees on each side), and the car brakes and accelerates straight. A little (or even a lot) of toe won't cause the car to pull if everything is truly symmetrical, but it will make the steering quite a bit more sensitive than some people are used to. -0.04 is pretty mild toe out, as things go.

 

[sgale]

So I’ll check the strut to knuckle bolts for torque and the strut nuts for being there and torqued. I am confused about which bits of the irs need to be clocked? And by clicked I assume you mean losened and then torqued while under load. Would you recommend the subframe bolts themselves? The guy I spoke to at lmr said he just loseened whatever he could reach inside the wheel well. Didn’t get under the car. Is that what you are referring to BmacIL?

Thank again for everyone’s input.

 

[BmacIL]

So I’ll check the strut to knuckle bolts for torque and the strut nuts for being there and torqued. I am confused about which bits of the irs need to be clocked? And by clicked I assume you mean losened and then torqued while under load. Would you recommend the subframe bolts themselves? The guy I spoke to at lmr said he just loseened whatever he could reach inside the wheel well. Didn’t get under the car. Is that what you are referring to BmacIL?

Thank again for everyone’s input.

All the rubber in the suspension should be clocked. The important ones are the forward/upper arm in the front, and the front inner point of the rear control arm. It's also a good idea to do the outer camber link.
https://www.mustang6g.com/forums/showthread.php?t=44129

 

[sgale]

Everyone thanks for all the help! That thread on clocking the rubber mount fasteners was super helpful! Now if only I had a 4 post lift!

 

[ForYourOwnGood]

All the rubber in the suspension should be clocked. The important ones are the forward/upper arm in the front, and the front inner point of the rear control arm. It's also a good idea to do the outer camber link.
https://www.mustang6g.com/forums/showthread.php?t=44129

I understand that when clocking the bushing the car should be level, what if you have no way to get it perfectly level? When I had my alignment done the shop had literally no idea what clocking the bushings meant and didn't seem too keen on trying it.

I've been trying to figure out the best way to do it myself and the closest thing I can come up with is since my driveway is a gentle slope using the rhino ramps on the downhill side to approximate level and do one end at a time.

 

[BmacIL]

I understand that when clocking the bushing the car should be level, what if you have no way to get it perfectly level? When I had my alignment done the shop had literally no idea what clocking the bushings meant and didn't seem too keen on trying it.

I've been trying to figure out the best way to do it myself and the closest thing I can come up with is since my driveway is a gentle slope using the rhino ramps on the downhill side to approximate level and do one end at a time.

That will be ok. The hardest part is getting enough clearance to swing a ratchet/breaker bar. Unfortunately rhino ramps don't cut it...ask me how I know.

 

[sgale]

All the rubber in the suspension should be clocked. The important ones are the forward/upper arm in the front, and the front inner point of the rear control arm. It's also a good idea to do the outer camber link.
https://www.mustang6g.com/forums/showthread.php?t=44129

Hey BmacIL, you say the important ones are the forward/upper arm in the front and the front inner point of the rear control arm. Could you elaborate on that? I wan to make sure I understand completely. Do you mean the front inner lower control arm and the outer control arm bolt? I'm referring to the wording cited by Coaster in the thread that you linked to. Not to be a hassle, but if you don't mind using that wording, that would help me clarify exactly which ones are most important.

Thanks!

 

[Nagare]

Did you see the pic on page 7? I don't know which one he was referring to, but the image definitely helped me to understand it better.

 

[sgale]

Now that you post that, I remember seeing it, I think I was just bogged down by knowledge at that point.

Thanks

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