What a tie rod actually does

A tie rod carries steering force to the wheel’s steering knuckle. In a rack-and-pinion system, the rack slides sideways and pushes or pulls the tie rods. Their ball joints flex as the suspension moves, so the steering keeps working while the wheel travels up and down. MOOG puts it simply: without tie rods, steering the car would be impossible. MOOG on tie-rod symptoms.

The inner tie rod connects to the rack, usually under a protective bellows. The outer end’s ball stud bolts to the knuckle. Nearby parts do other jobs: a control arm locates the suspension, a CV axle carries drive torque, and a stabilizer link connects the anti-roll bar. Tracing the rod to where it attaches is more reliable than spotting it by the rubber boots. MOOG shows inner and outer tie-rod constructions.

Inside, the joint is a ball and socket. Replacement designs add features to slow wear and loosening:

• heat-treated ball studs;
• spring (Belleville) washers that keep preload as the bearing wears;
• grease fittings that let new lubricant push out contaminants; and
• wrench flats for setting the length.

MOOG.

A steering linkage is another layout

Not every tie rod connects straight to a rack. On a steering-box car, the box can move the tie rods through a center link or drag link. The Mustang photo shows that kind of linkage, which still moves the spindle. “Inner” and “outer” have to be read in the context of each layout.

Length sets toe

Changing a tie rod’s effective length changes toe: which way the wheels point relative to each other, seen from above. Brake & Front End notes that small amounts of wear in each joint can add up to a big change in toe. Brake & Front End.

MOOG says the old habit of counting turns when swapping an outer tie rod no longer finishes the job. Toe on the side you worked on is likely to be out, and as the car drives, toe “equalizes,” leaving both sides off. Being out by just a degree can wear both front tires. Lane-keeping, stability control and automatic emergency braking all rely on the steering-angle sensor, so it needs recalibrating after the alignment. MOOG explains the alignment consequences of outer tie-rod replacement.

Checking one properly

MOOG lists these symptoms:

• uneven tire wear;
• pulling or poor tracking;
• a steering wheel that shakes or feels loose; and
• clunking in slow turns, or grinding if a torn boot has let dirt in.

MOOG. Many other steering and suspension faults cause the same symptoms.

Brake & Front End explains the inspection:

• The boot matters most. Its top killer of tie rods is a damaged boot. Modern sealed joints can’t be flushed, so a torn boot means replacing the end.
• Check at ride height. Wear forms an oval in the socket, so a joint can feel tight with the suspension hanging. With the car on its wheels, an assistant rocks the steering while you watch.
• Use hands, not a pry bar or pliers. Ford and other manufacturers say this, because force reads bushing movement, and pliers can make even new joints seem worn.
• Make sure the play is in the joint. Play at the inner rod can be a loose rack instead.
• Use the specified torque. Tie-rod studs in aluminum knuckles are often torque-to-yield and fitted dry.

Brake & Front End. An intact-looking boot doesn’t prove there’s no play inside. Follow the vehicle’s alignment and calibration requirements after any work that changes them.