A pull to one side with a drift in a straight line can have many causes.
The Straight-Road Drift Test
Most car manufacturers conduct first checks by going for a test drive on a flat, straight road. The motorist drives slowly at first (around 30mph) and gently releases the wheel. The car will drift off in a particular direction. If there is any serious pulling then the test is repeated at a slightly higher speed to establish whether or not the problem gets worse. The causes of pulling or drifting could be associated with the tires or with the steering system.
Checking the Steering Wheel Centre Position
The steering wheel of a car that is parked on level ground will sit in a straight line if all is well. If it’s not perfectly central but the car does not pull to one side, then it will indicate that the car is not tracking properly. However, if the steering wheel is not central and there is also a tendency for the car to pull in one direction, then this suggests that the rack is not in its neutral position.
Ruling Out Tyres First
Most Power Steering Specialists will normally check the tire pressures of all four tires and look for uneven wear of the treads. Often a single tire, even if it is only 4-5 psi below the recommended pressure, can cause a vehicle to pull.
Checking for Uneven Rack Resistance
Turn the steering wheel slowly through the lock and check for any stiff spots or unusual resistance. Uneven resistance as the wheel goes through the full lock could indicate worn internal seals or even a damaged valve body. A useful reference for Power Steering Specialists is https://westernpowersteering.co.uk/.
Reading the Alignment Figures
On the 4-wheel alignment rig the figures for toe, camber and caster are compared with those of new cars of the same make. Even a castor difference of as little as 0.5° side to side can cause constant drifting, even when all else appears to be in order.
As all causes of drift are simple to rule out prior to opening up the car for repair, it is easy to diagnose the problem before any parts are ordered or fitted.
