TECHNICAL TIPS

Memory Steer

Application: Pickup Trucks/ Cars

Background: We get this question several times a week from the Tech Line.

By: Doug Hardy, National Trainer/Technical Services

Bulletin: What is memory steer and what can cause it?

Memory steer can happen in all types of vehicles. Normally the symptoms include the vehicle wanting to pull left after a turn to the left and/or the front end wanting to pull right after turning to the right. This is typically caused by one of the pivot points binding in the suspension system or the steering linkage.
On MacPherson strut front wheel drive vehicles this is usually caused by the upper strut mount. It can happen at any time but usually occurs on high mileage vehicles right after the strut has been replaced. The upper bearing plate has been moved out of its normal wear area and now wants to bind up in a turn or the bearing plate can be sagging and contacting the strut tower. Either way the bearing plate needs to be replaced. It’s always a good idea to check the bearing plate or bearings and replace them when replacing the front struts or springs.
On Ford and Dodge Trucks sometimes a memory steer will happen after replacing one of the caster/camber sleeves on the upper ball joint. To correct this condition it is recommended that you break the taper on both the upper and lower ball joints, center the steering, and retighten both ball joint stud nuts to specifications. This relieves the bind that may occur in the ball joints that can be caused by installing a sleeve with close to maximum correction.
Another area that can cause memory steer is the rubber bonded socket (RBS) tie rod ends used on some Ford cars and trucks. The proper way to install this tie rod end is to have the steering pointed straight ahead as you tighten the stud nut. If it is tightened off-center, the bushing rubber material in the joint acts like a spring wanting to return to its installed position and can cause a memory steer condition. Fortunately, most of these tie rod ends had a high failure rate and normally were replaced with a standard greaseable ball type tie rod end. But there are still some out there.

Additional Tips:
* Sometimes an unbalanced power assist or a binding steering gear can cause a pull to one side or a memory steer condition. Check for power steering problems by lifting the front of the vehicle off the ground and then starting the engine without touching the steering wheel. Rev the engine up a bit and see if the steering wheel wants to move in its own. If so, you many have a leaking spool valve. On most rack and pinion and Saginaw type steering boxes, movement during this test indicates that you need to replace the gearbox. If you have a very old Ford, Corvette, or some other car with the assist piston mounted on the steering linkage you should be able to adjust the centering valve to eliminate pressure bleeding to one side or the other and eliminate the pull.
* You may have to drop the tie rod ends or remove the linkage from the pitman arm to find a neutral valve problem. This is a good time to detect binding in the spindles, re-examine the tie rod ends, and re-inspect the ball joints. It normally takes about 30-35 pounds at the outside of the tire to steer the tire from side to side. What you are looking for is one spindle steering much harder than the other or binding at some point. This test should be performed with the weight on the turn tables & with the tires off the ground.
* If someone has adjusted the steering gear sector shaft too tight, this can also cause a bind on turns and the steering wheel may not want to return to center. If the gear has too much play when centered but binds in turns, the sector shaft to ball nut teeth are probably worn out. Usually, this requires replacement of the steering gear.
* If there is still no answer, isolate the brake. If the vehicle is pulling to the right "backset" the right hand caliper and clamp off the hose. Very carefully drive the vehicle to see if the pull is gone. If the car no longer pulls, it is that brake.
* Do not overlook the rear brakes. A dragging rear brake will have the same effect as a front brake.
* On the I-beam Ford trucks you may need to increase the caster offset to correct a pull. The older trucks may require up to a 2 degree caster spread to correct a pull.
* Don’t forget to spin the tires to see if a bearing is dragging and causing a pull.


RDTSB/02/005
Issue Date:
October 15, 2002