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New alignment, still very twitchy. Think I don't have enough caster.
So first question, how does caster get messed up on these cars to start with, and second - how do I fix this? The car is unstable enough at normal driving speeds that it is 100% hands on wheel full attention, would-not-let-someone-else-drive twitchy. And not like a race car set up for quick turn-in.
As far as I can tell, the car's had no accidents. I've had the nose off and spent a good bit of time underneath so I think I would have seen repaired damage. 67k miles, oem Sport suspension with coupe 19" wheels, Kumho PS91 tires in 245 and 275.
Were the struts ever replaced? We might be digging into very weird questions.
Caster leads me to think: Bent strut, spindle or mislocated strut tower, but sounds extreme if the car was never in an accident. Could it be that this is affected by a strut replacement (like missing gaskets on top of the gasket, missing spring isolators, incorrectly torqued bolts)?
Last edited by Carboy37; Sep 30, 2020 at 04:31 PM.
Did you ever fix this issue Mike? I’ve been silently reading this thread’s updates for months. I hope you do get it sorted out. Are all the struts tightened well onto the chassis?
I actually got a chance to poke at it yesterday. TL;DR: I think the upper control arm bushings are shot.
Wheel/tire and brake assembly looked good. No visible damage - looked at a junkyard car (hit in the rear) over the weekend and took reference pics. Struts do not affect front alignment on this car - upper and lower control arms. Lowers were tight with little flex. Uppers... well, for a 3000 lb car, I shouldn't be able to wiggle them easily.
Wanted to add - what you're seeing with me wiggling the control arm front to back is a direct change in caster. Not sure if that is still present under loading (had car on stands with wheels off) but I imagine it would be.
The thing that bothers me is that all three alignment techs assured me they pried and pounded on everything and it was all OK.
I think your bushings are fine, from the video. They move after you load them up...but they spring back.
Rubber bushings don't (can't) hold dynamic alignment angles. Bushing deflection will allow your alignment angles (Toe/Caster/Camber) to constantly change as you drive down the road, even when the car is brand new.
Additionally, all the alignment angles change as the suspension cycles through its bump cycle.
You'd be surprised how much dynamic change in angle it actually takes to cause instability.
As far as your issue goes...
Any chance you're using Hankook V12 EVO's?
Those are famous for excessive tread squirm. Lots of people report a strange instability and delay in steering motion when they get new V12's.
Your issue indicative of squirmy tyres, whatever brand they are. Do you have a spare wheel/tyre set you can try out to eliminate that hypothesis?
If it is tread squirm...you can wait for them to wear down. It will get better with wear.
Or you can buy a different tyre.
If you do get new rubber bushing UCA's....remember to tighten the bushings down only when the car is resting at ride height.
Not so fun fact that nobody except me finds useful:
Factory bushings are also designed with specific durometers and sizing. Their controlled deflection also helps stabilize the car because they work/deflect as a system. Aftermarket bushings do not have this type of systematic engineering. So you should choose type, durometer, and function of your aftermarket bushings carefully. You're the engineer captain now.
Last edited by Hugh Jorgens; Oct 20, 2020 at 11:30 AM.
Do Infinti's have sequential bore sizing for the front and rear wheels so you can't mix them up?
Maybe someone put a rear wheel on the front on one side?
This happens on S2000's. They have sequential bore sizing. People mix up the stock wheels. Instead of stopping when the wheel is resisting, they just keep torquing the lug nuts down. The wheel goes on. Ruins the hub bore. Potentially ruins the hub, bearing, and rotor. Causes all kind of issues. Etc.
No, Kumho PS91s. I haven't read anything negative about them and I just searched again.
I tried levering them while sitting on the ground with tires - still very easy to move. Tried same thing with the wife's CX5 (similar weight but MacPherson strut suspension) and the LCA doesn't move at all, nor does the strut top. I don't have another dual control arm to check, but the wrecked G37 I took reference pictures of didn't flex that much.
I'm putting only a tiny bit of force on there - the lever is roughly 2' long and I'm putting maybe 1-2 pounds of force - the kind of pressure if you reached out to a friend to give their arm a reassuring squeeze.
Do Infinti's have sequential bore sizing for the front and rear wheels so you can't mix them up?
Maybe someone put a rear wheel on the front on one side?
This happens on S2000's. They have sequential bore sizing. People mix up the stock wheels. Instead of stopping when the wheel is resisting, they just keep torquing the lug nuts down. The wheel goes on. Ruins the hub bore. Potentially ruins the hub, bearing, and rotor. Causes all kind of issues. Etc.
No, and I checked - both front wheels are the coupe 19x8 with 245 tires.
I also put the aftermarket 20s back on the front and roadtested - twitch is still there.
But the issues started right when you got the wheels and tyres, is it?
65K miles is extremely early for a factory-supplied bushing failure.
Has the suspension ever been modded? I know you mentioned its currently stock.
I got the car in May of 2018; if anything was changed, it was changed back before I got it. Only modification I saw was an amp wire in the trunk and the 20" wheels.
