From the viewpoint of a technician, one of the first things we think of when installing a knuckle/hub assembly is the time it will save us. This is a beneficial advantage, and even though we are usually skipping the “hard” parts of the job, there are still many critical aspects of it that mean the difference between a job that is done, and a job that is done right.
Here’s a look at the most critical points of the job.
Attachment Points
Ball joints and tie rod ends are secured by either a pinch-bolt or taper-fit type of attachment, and either of these can be damaged by over-tightening. For a pinch-bolt attachment, be sure to thoroughly clean the ball stud on the ball joint or tie rod end. Built up corrosion can affect the installation.
Whether it be a ball joint or tie rod end, they should slide easily in place into the steering knuckle with no hammering or excessive force. Always be sure to torque any pinch bolts to the proper specification. Over-tightening can distort the hole and damage the ears on the knuckle. Since the pinch-bolt design is subject to corrosion, the shank of the bolt is a great place to use a small amount of anti-seize compound to prevent this from happening in the future. Remember, don’t use anti-seize on the threads because it will affect the torque.
For a taper-fit attachment, clean the threads on any ball stud so you can install the nuts by hand. Never use an air tool, because you can easily overtighten the ball stud, which can distort and damage the taper, pull the stud too far through the knuckle and lead to a loose fit, as well as the possibility of a broken ball stud.
Always use the correct torque specification when tightening a taper-fit ball joint or tie rod end, and always install a new cotter pin where one is utilized. A sign of a taper fit that has been over-tightened is one in which the hole for the cotter pin is well above the castle nut.
To Grease or Not to Grease
It’s a common question, should you grease the splines of a CV joint before sliding it through the wheel hub? The answer is no. These are designed to be clean and free of rust or lubricant, which means no grease and no anti-seize. Since a knuckle/hub assembly has a new hub, you’ll just have to clean the end of the CV joint.
The Axle Fastener
No single torque specification can be considered more important than another, but one from which you may notice the most immediate affect is that of the axle fastener. Be it a nut or a bolt, old fasteners can fatigue and lose their ability to maintain the proper clamping force, which plays an additional role in the case of a wheel bearing. The torque specification is designed for far more than just keeping something tight. In the case of wheel bearings, it is designed to maintain the proper amount of preload in the bearing, which in turn affects the geometry of the rolling elements to the bearing race. If this isn’t correct, the bearing simply won’t last as long.
The torque specification for many axle fasteners is often one of the highest ones on a vehicle, making it difficult to achieve and also increasing the temptation to use an impact wrench. The bottom line is, never use an impact to install an axle fastener. The repetitive shock from an impact wrench can cause permanent indentations in the bearing races.
This is a common mechanical occurrence called brinelling, and it can happen to many different types of bearings in many different situations. While we see this mistake most commonly with front wheel bearings, the best practice is to never use an impact where bearings are concerned.
There are different methods to tightening the axle fasteners. You can have an assistant hold the brakes, and another common method is inserting a punch into a vented brake rotor and allowing it to rest against the caliper bracket. Some manufacturers recommend a certain torque, then resting the vehicle on the ground to perform the final torque. Always follow manufacturer specifications.
Don’t forget the proper torque on the wheel lug nuts, and, last but not least, you should always perform a vehicle alignment when any suspension component is replaced.
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