Torque Steer in DB9 2008

[Dubsands]

Looking for some advice on the following,

Driving at slow speeds in a turn and applying a modest amount of throttle my DB9 wants to go Right, on easing off the throttle it "shifts" back to the originally steered course. This is by the "seat of the pants", there is no movement in the steering wheel but the car wants to go right. It also happens when on the straight, doing 100km/h and give it a modest throttle input the car wants to go right and as soon as you take the throttle off back towards straight ahead. The car rides straight under all other conditions except this tendency to "Pull" to the RIGHT when adding a bit of throttle/torque. Despite the following list having been carried out the issue still persists;

Replaced all tires, with correct tyre pressure and tracking
Drained and replaced rear differential oil (No leaks, it wasn't filthy dirty and no metallic bits in the old fluid. Replace with Motul Gear LS 75W/90). The differential did have a bit of chatter prior to the oil change when cold and in a turn, like from drive way onto road, but this disappeared completely after just a few 100m. After the differential Oil change no chatter at all
Brakes checked for binding but nothing untoward found
Dampers all checked and nothing abnormal found
Main wheel bearings checked front and rear, again no abnormal play
Track rod ball joints and suspension all checked and nothing bent, broken or loose

Any ideas of what could cause this? Is it a normal feature in a rear wheel drive car with a modest amount of torque at its disposal? What is the next step in order to try and eliminate this tendency, if it is not normal?

[pschlute]

My 2005 DB9 never did that. It did however have a left turn bias when coming off the throttle at speed. Getting the wheels set up properly with a Hunter machine solved it.

[8Tech]

Check alignment and have the rear ballpoint and bushes rechecked. Sounds like the car is trying to steer from the rea. Use a lever to check for play, oh will never feel it just with has pressure.

[ds666]

It isn't torque steer as such ( which is normally linked to front wheel drive cars ) , think it is to do with what is called the " thrust angle " .
A good geo reset should sort it but perhaps there is some damage in the driveline from , for example , hitting a kerb ?

[Dubsands]

ds666 said:

It isn't torque steer as such ( which is normally linked to front wheel drive cars ) , think it is to do with what is called the " thrust angle " .
A good geo reset should sort it but perhaps there is some damage in the driveline from , for example , hitting a kerb ?

Thanks for the input ds666, I think you are correct in respect of the thrust angle. There is no history of damage to the suspension or wheels, they are all original. I will take it back for another alignment starting from scratch, I have the standard settings but may have to tweak them just a little bit (a little less toe in on the front and rear) to get the right feel and maintaining a neutral thrust angle.

[LTP]

Dubsands said:

Thanks for the input ds666, I think you are correct in respect of the thrust angle. There is no history of damage to the suspension or wheels, they are all original. I will take it back for another alignment starting from scratch, I have the standard settings but may have to tweak them just a little bit (a little less toe in on the front and rear) to get the right feel and maintaining a neutral thrust angle.

i think you need to do things in the right order. You need to get all the bushes in the rear suspension and the subframe mount checked before you get an alignment done, because if you've got a soft bush you're just wasting money aligning with it in place and it'll probably need doing again once the bush is fixed.

[Dubsands]

LTP said:

i think you need to do things in the right order. You need to get all the bushes in the rear suspension and the subframe mount checked before you get an alignment done, because if you've got a soft bush you're just wasting money aligning with it in place and it'll probably need doing again once the bush is fixed.

Thanks for the input, double checked all bushings, bearings, inflated tyres to correct pressure, full tank of fuel and then back onto a Geometric align. Front end all within spec. Rear Right excessive toe in, rear Left excessive toe out. All adjusted and torque vector down the middle. Test drive under modest throttle now simply lifts nose with no pulling left or right. For now the issue is fixed. I am still at a loss as to why the original settings after the new tyres were in place was showing as correct and then after 2 weeks and 250km it needed re-alignment. The only observation on the second alignment, the technician was also using a horizontal line (in line with the axels) and a tape measure. I thought that this was all done accurately by lasers etc.

[LTP]

Dubsands said:

I thought that this was all done accurately by lasers etc.

So did I. But, to be fair the toe-in/toe-out findings you reported are consistent with the rear wanting to move to the left, so the car would want to steer right. I guess it's not the alignment kit being used it's the knowledge and experience behind the kit that counts.