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Pelican Technical Article:

Replacing the Steering Knuckle

Mike Holloway

Time:

4 hours4 hrs

Tab:

$250 to $1300

Talent:

***

Tools:

14mm, 17mm, 19mm wrenches or sockets, needle nose pliers, large flathead screwdriver, floor jack, jack stands, wheel chocks, safety glasses, lug wrench, torque wrench

Applicable Models:

Mercedes-Benz R107 (1972-80)

Parts Required:

Steering knuckle with ball joint

Hot Tip:

Don't remove the shock absorbers. Both control arms will have to be replaced.

Performance Gain:

Better handing, less vibration, smoother ride, and increased tire life

Complementary Modification:

Replace shock absorbers

As you drive your car your front suspension needs to do two jobs. It needs to pivot left and right in the direction you want to turn. It also needs to move up and down with suspension movement. Bushings are not capable of this kind of flexibility. In rear suspensions you can use more bushings, because there is no left to right steering movement. Ball joints are used to allow the steering angle to change with any up and down movement of the suspension. Mercedes-Benz uses two control arms, an upper and a lower to allow the spindle to move up and down with suspension movement and still allow the steering input to pivot the spindle. The lower ball joint is serviceable separately. The upper ball joint is built into the upper control arm. This means to service this component you need to replace the whole upper control arm. With all this left and right movement and up and down suspension movements these ball joints can wear out. When a ball joint wears out the spindle is allowed to move around while driving causing noises during suspension movement and also uneven tire wear.

In this tech article we will go over all the steps to remove the steering knuckle. In order to do this the upper control arm with built in upper ball joint will have to be removed. These fasteners are going to be tight, and there may not be a lot of room to swing the wrench. You are going to have to be patient and use some force to remove fasteners and components to rebuild your front end. Corrosion may hold a component in even after you have loosened a fastener. Keep in mind the joint may pop out when you use a removal tool so keep your hands clear and wear protective gloves. When this happens it will scare the heck out of you. I know this for a fact because it scared the heck out of me when it popped.

Steering knuckles connect the tie rods, shocks and control arms to the wheels and brakes. The spindles on the knuckles also carry the wheel hub bearings. If the spindles get damaged you can have all kinds of trouble, and the only solution is replacing the knuckles. In order to remove and replace the steering knuckle, you will have to free it from the upper control arm as well as the tie rods. Once that has occurred it can be removed from the wheel. You may wish to remove the front brake calipers to provide more room. It is optional.

Lift and support the front axle of the vehicle. You have to remove the tires to perform this job, and it does make access much easier since you may not have access to an automotive lift. See our tech article on jacking and supporting your vehicle and removing the front tires. The procedure to replace the front upper ball joint is the same for both the left and right side. In these pictures we are working on the passenger side. Keep in mind all the steps apply to both sides. It is recommended you replace both sides at the same time to keep your handling neutral.

Remember that your car may have been serviced before and had parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches.

Before you do any work on your car it is important that you wear safety glasses and work gloves. If you have to jack up your car, make sure to use jack stands and chock your wheels as well as applying the parking brake. Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. Never work on your vehicle if you feel the task is beyond your ability. Always disconnect the battery before working on your car.


Lift and support the front axle of the vehicle.
Figure 1

Lift and support the front axle of the vehicle. Place a jack stand under the lower control arm. You have to remove the tires to perform this job, which makes access much easier since you may not have the use of an automotive lift. See our tech article on jacking and supporting your vehicle and removing the front tires. 

I placed a jack stand under the chassis as well.
Figure 2

I placed a jack stand under the chassis as well. The procedure to replace the steering knuckles is the same for both the left and right sides. These pictures are of the passenger side of the vehicle. It is recommended you replace both sides at the same time to keep your handling neutral. Placing a jack stand under the chassis provides additional safety.

The steering knuckle (red arrow) is fixed to the wheel assembly as well as the tie rod and upper control arm ball joint.
Figure 3

The steering knuckle (red arrow) is fixed to the wheel assembly as well as the tie rod and upper control arm ball joint.

Do not remove the shock absorber. The first nut to remove is on the steering knuckle.
Figure 4

Do not remove the shock absorber. The first nut to remove is on the steering knuckle.

Using a 19mm open-end wrench, loosen and remove the nut from the ball joint..
Figure 5

Using a 19mm open-end wrench, loosen and remove the nut from the ball joint.

You may choose to remove the brake line.
Figure 6

You may choose to remove the brake line. I was able to remove the upper control arm without having to do this step but as long as you are there, you can look to bleed the lines of air if they feel squishy or you want to change brake fluid. 

Using a 14mm line wrench, loosen the brake line.
Figure 7

Using a 14mm line wrench, loosen the brake line. Make sure you have the proper receptacle to collect brake fluid if you decide to do this step. Again, it is optional and not required to carry out the removal and replacement of the steering knuckle.

The steering knuckle is connected to the tie rod.
Figure 8

The steering knuckle is connected to the tie rod. In order to free the steering knuckle, it has to be removed from the tie rod. The tie rod is connected with a crown bolt held in place with a cotter pin.

Using a pair of needle nose pliers, remove the cotter pin.
Figure 9

Using a pair of needle nose pliers, remove the cotter pin.

Using a 17mm wrench, loosen and remove the crown bolt.
Figure 10

Using a 17mm wrench, loosen and remove the crown bolt.

Using a separating tool, apply slow pressure to remove the connecting bolt.
Figure 11

Using a separating tool, apply slow pressure to remove the connecting bolt. Please keep in mind that there may be a 'pop!' when it gives way. It will scare the heck out of you but that will be the extent of it.

Using a separator tool, fix it to the ball joint and slowly turn the tools screw to begin to separate the ball joint from the steering knuckle.
Figure 12

Using a separator tool, fix it to the ball joint and slowly turn the tools screw to begin to separate the ball joint from the steering knuckle. Again, please keep in mind that there may be a 'pop!' when it gives way. It will scare the heck out of you but that will be the extent of it. 

After the ball joint is free, the upper control arm should be able to move up and down.
Figure 13

After the ball joint is free, the upper control arm should be able to move up and down. Move it back and forth in order to gauge the amount of play there is on the bushings.

The steering knuckle is held in place with two bolts.
Figure 14

The steering knuckle is held in place with two bolts. In order to make sure the bolts do not loosen, there is a bendable flange to keep them in place (red arrow). This can be bent back with a flat face screwdriver. 

The steering knuckle is held on with two bolts. Using a 19mm wrench, loosen and remove the two bolts.
Figure 15

The steering knuckle is held on with two bolts. Using a 19mm wrench, loosen and remove the two bolts.


The steering knuckle is now free to replace. Installation is the reverse of removal.
Figure 16

The steering knuckle is now free to replace. Installation is the reverse of removal.

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Page last updated: Sat 10/21/2017 03:10:14 AM