sccadriver

I did a search and came up with the track day suspension set up. That didn't answer the question that I have. When I am driving on a straight road, usually above 40mph, she is kinda slightly has a immediate pull (like a quick movement of the car, easily corrected with a slight steering wheel movement to counter act) to the right. She does the same thing to the left when I let off the throttle. Does anyone have any ideas what may be the issue?

JCrane82

iTrader: (3)

alignment, tire pressures, crown in the road......all of these could explain a tendancy for the car to drift off line.

Does it do it regardless of the crown in the road? Can you test it in a parking lot with no crown?

9krpmrx8

iTrader: (46)

Sounds to me like Radial Pull (Google it).

RIWWP

iTrader: (2)

If the pull to the right happens only on applying throttle, and the pull to the left happens only on letting off the throttle, then check your tire sizes for the rear tires, confirm that they are the same size. If they are, then check tire pressures and ensure that they are the same pressure.

A total diameter difference between left rear and right rear will change the LSD application, and you will get that kind of reaction.


It is unclear if the initial pull right is related to accelerating or not though.

sccadriver

I have checked it several different ways. All the tires are the same size, same tread depth and air pressure is correct. It does it on any road surface including new black top road, no ruts. It is directly related to throttle up and down. Not just on and off the throttle, but slight press on the throttle and slight release of the throttle. The best way to describe it is like a front wheel drive torque steer. Could it possibly be that I need the rear differential serviced?

RIWWP

iTrader: (2)

If I were to ignore that you already checked stuff, I'd say that it confirms a difference in left rear vs right rear torque delivery, including negative torque.

I experienced this in the 8 as well as in a Miata with a rear LSD. In both cases, there was a problem with the tire pressures in the side that it pulls toward on decel, where the air pressures would dip too low, reducign the overall diameter and effectively increasing the rolling speed of that wheel/tire. The LSD is designed to act on a difference of torque, and so the result would be a pull to one side on acceleration, and a pull to the other on deceleration.

Since the axle splines are fixed diameter, the hubs are fixed diameter, the wheels are fixed diameter... the only thing that can change diameter on the diff-to-tire line is the tire, and it can do so with air pressure easily.

If everything is literally identical left to right and the problem still exists, then logically it would have to be a diff problem. The only diff problem I've seen outside of racing on the forums in 7 years was someone forgetting to put the fill plug back in, sprayed the fluid out on the road and siezed it up. However, tire pressure problems are not only common, they are reasonable.

I say re-check everything carefully to make sure they are the same. The overall diameter is the key metric, so if the pressures are the same, get out a tape measure and measure the diameter.

JCrane82

iTrader: (3)

swap left rear tire with right rear tire and recheck. If it is due to pressures/diameters, then you should get the opposite pull.

sccadriver

I too my tech for a ride while at lunch, just after setting the tire pressures. It still did the same thing. After a short drive we went through Mickey D's drive through. When pulling forward and turning he heard a light crunching noise. He said the next step is to drain and fill with the proper mix of fluid and friction modifier. I will keep everyone posted after that gets done.