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Rear End Sway- Problem?

Jobodizo

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JAJ

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Howdy all. I picked up a 2017 GT350R a few weeks ago and man, its so good. After having multiple high performance cars (Porsche's mainly) the rear end of the car, under load through a corner, feels very wrong and unstable. Not a loosing traction and going into oversteer type scenario, almost like the rear end of the car is swaying and/or walking. I haven't gotten it out to the track yet, but on the road (highway interchanges, and some, not all corners) the rear end of the car feels very unsettled, in a dangerous way. Its to the point where I've pulled over and made sure that there isn't a loose wheel or suspension component. I understand that these cars tramline pretty hard, and with the track alignment on the car, I get that can be exaggerated on anything less than perfect pavement, but has anyone else experienced this? I'm on PS4's right now 305/315 staggered. The car was set up by the previous owner so not sure of alignment spec's but definitely in the -3 range up front (unsure of rear). It does have camber plates but after looking over the car, all other suspension components are stock. Is it grooved pavement or expansion cracks that could be causing this sensation? All components (bushings/bolts) are fine and torqued as needed. Am I going crazy? As mentioned, I can take some corners and this thing is like a go cart, but others its just extremely unsettled and feels dangerous. Thoughts?
Get the rear wheel alignment checked. I had a similar experience in my GT350 (non-R) with MPSC2 tires coming back from a track event. Tires were heat cycled out and the car just wouldn't go in a straight line - after 200 miles my arms were sore. Checked the alignment - front (that I had adjusted) was perfect but rear toe was (as set from the factory) at around 0 degrees, versus the 0.3 degrees total toe-in it's supposed to be. 0.3 Degrees is a microscopic change, but once the rear toe was corrected, it was a different car.
 
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TRCKWMD

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Appreciate the input. I'll take a look at what y'all mentioned and report back. Sounds like i've got a good starting point to isolate the problem.
 
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People on the forum refer to that as the "rubber band effect." What you're probably feeling is lateral movement in the big rubber bushings that isolate the rear IRS subframe. Does it tend to happen more over corners when there is a slight bump or crowning that would unload the weight on the springs? Like @cmxPPL219 mentioned, grab yourself some of these and some of these and that'll probably fix you up.
That's about as accurate of a sensation as I can relate to. Its not every corner but when its off camber or grooved pavement, that's when I really notice it.
 

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OP, I’m in the south metro area. My car won’t come out to play for another couple of months, but if you want to use my car as a comparison we could meet up sometime in early May. My wife and I do the Morrison to Evergreen run A LOT during the summer and that drive can test the car if there aren’t too many bikers (the spandex wearing kind) on the road. I’m sure you’ll have it sorted by then, but if you want something to benchmark off of, I’m willing to step in.

My car has a relatively new set of Cup2s (thank you @SheepDog) and I have the FP track alignment so it won’t be apples to apples with the 4s but should be enough to compare for rear stability. PM me if you are interested.
 

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OP, I’m in the south metro area. My car won’t come out to play for another couple of months, but if you want to use my car as a comparison we could meet up sometime in early May. My wife and I do the Morrison to Evergreen run A LOT during the summer and that drive can test the car if there aren’t too many bikers (the spandex wearing kind) on the road. I’m sure you’ll have it sorted by then, but if you want something to benchmark off of, I’m willing to step in.

My car has a relatively new set of Cup2s (thank you @SheepDog) and I have the FP track alignment so it won’t be apples to apples with the 4s but should be enough to compare for rear stability. PM me if you are interested.
Thanks man! Hope to have it sorted by then and appreciate the offer! Where about are you? I’m in Parker
 

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Thanks man! Hope to have it sorted by then and appreciate the offer! Where about are you? I’m in Parker
No problem at all. I’m in Highlands Ranch. We do the Vehicle Vault car show a few times each year too.
 
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Well, i think I have found the culprit. Still going to get an alignment done just to verify that's on point, but went under the car to look for bushings that might be bad, none. Checked all sway bar end links, all tight and torqued to spec. Decided, hey, why not get a torque wrench on the lug nuts and see if my early suspicion was right being a loose lug nut (shame on me for not doing this sooner) and BINGO. Front lugs were torqued to about 90lb/ft, rears marginally better at 100lb/ft. Torqued to the specified 150lb/ft (well, 145lb/ft) since the owners supplement gives a 15lb/ft buffer. With the tire pressures down to 32psi and lugs torqued down, issue seems to be resolved. The dealer that I bought this from mounted 4 new tires prior to purchase and fixed a shock that was leaking so I know the wheels were off prior to purchase and guessing they just didn't re-torque properly. Will update after an alignment and let you know what the measurements were at.
 

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I am one of those that checks tire pressures weekly and when there are swings in temperatures from the last time I drove the car on the street. I also check wheel lug torque about every month. It is not unusual to find a few that are a bit low once in a while.

Anytime that the car has been to a shop for any work requiring the wheels to be removed I am there and tell the wrench working on it to torque to 150ft. lbs. EVEN THEN, when I get it home I recheck wheel torque.

At most shops I have been to the “Technicians” have no clue of how to properly torque something. More often than not they have a 3’ torque wrench that has not been calibrated since it was unloaded off of the ark and they masterfully torque the lugs at warp speed and bounce on the wrench 3-4 times “just to make sure”. That is if they don’t use the 3-4 uggas is just right method.

I recommend that you have a good quality wrench ( this does not mean that it has to cost $600 ) and that you use it regularly, and especially after any shop touches your car. If you don’t already have one, you will not make a bad investment in buying one. And, chances are that you will see fit to have others suited for other purposes.
 
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TRCKWMD

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I am one of those that checks tire pressures weekly and when there are swings in temperatures from the last time I drove the car on the street. I also check wheel lug torque about every month. It is not unusual to find a few that are a bit low once in a while.

Anytime that the car has been to a shop for any work requiring the wheels to be removed I am there and tell the wrench working on it to torque to 150ft. lbs. EVEN THEN, when I get it home I recheck wheel torque.

At most shops I have been to the “Technicians” have no clue of how to properly torque something. More often than not they have a 3’ torque wrench that has not been calibrated since it was unloaded off of the ark and they masterfully torque the lugs at warp speed and bounce on the wrench 3-4 times “just to make sure”. That is if they don’t use the 3-4 uggas is just right method.

I recommend that you have a good quality wrench ( this does not mean that it has to cost $600 ) and that you use it regularly, and especially after any shop touches your car. If you don’t already have one, you will not make a bad investment in buying one. And, chances are that you will see fit to have others suited for other purposes.
alignment done and the left rear was .78° toe out. That will do it. Fixed that and got it back to spec. Totally new car.
 

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alignment done and the left rear was .78° toe out. That will do it. Fixed that and got it back to spec. Totally new car.
There you go. I don't tighten lug nuts beyond 110 up front, and 120 rear. I know what spec says, but it's not necessary to go that high.
 
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TRCKWMD

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Oh that would have made for very exciting times.
Oddly enough, now that its back to the correct toe angles, its tramlining WAY worse than before but the turn-in issue is gone and its on rails in the corner. Need to get the front and rear camber dialed as well, just had time to fix the toe at my dealership the other day. Front is at -3.6 and rear is -2.2. She's set up pretty aggressive right now. I'll get that set back to the street setting after my autoX event this weekend.
 

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There you go. I don't tighten lug nuts beyond 110 up front, and 120 rear. I know what spec says, but it's not necessary to go that high.
I would follow the manufactures recommended 150 ft/ lbs. They won’t warranty things that break if your wheels are loose. If you run stock wheels and stock lugs then you’re not even close to the required torque to surface area.
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