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Overview and Diagnostics of the Front Suspension
 
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Pelican Technical Article:

Overview and Diagnostics of the Front Suspension

Mike Holloway

Time:

30 minutes30 mins

Tab:

$0

Talent:

*

Tools:

Small pry bar

Applicable Models:

Mercedes-Benz R107 (1972-80)

Hot Tip:

Wear work gloves

Performance Gain:

Better handing and smoother ride, eliminate clicking noise when changing directions or going over bumps

Complementary Modification:

Replace the struts

If you are starting to hear a knock sound when you go around a corner there is a good chance your bushings are starting to go bad.  Bushings can be found on several components of the suspension and steering mechanisms.  These bushings get a lot of wear and tear and can see a lot of oil from the engine as the car ages. They do wear out and should be checked every 30,000 miles.  A very easy and straightforward way to assess the bushing health is to grab it and move each component back and forth to feel any play.  You can also use a small pry bar and attempt to move the various rods and arms up and down.  These mechanisms should not have any play in them.  The most common indications of suspension and steering component wear would be:

  • Squeaking when turning or hitting bumps
  • A loose, sloppy, or floating feel when steering
  • Shaking in the steering wheel when going over bumps
  • Tire wear on one side or the other - not to be confused with wear from misalignment

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. 

The following are the various components that make up your front-end suspension:

Tie Rods: Tie rods are attached to the steering idler arm.
Figure 1

Tie Rods: Tie rods are attached to the steering idler arm. The tie rods direct the wheels by pushing and pulling the front tires as the steering wheel is turned. Tie rods fail due to wear and tear. Tie rods longevity can be affected by certain driving conditions. Driving obstacles like potholes, poor road conditions or even minor accidents can cause tie rods to work incorrectly. Because of their importance and high usage, you should inspect them regularly. If you don't get your tie rods inspected on a regular basis, there are some warning signs to look for. If your vehicle pulls to one side while driving, or when braking, it's possible that bad tie rods may be the culprit. Your vehicle's tires will also show uneven wear on the inside and outside edge of the tire when there's a tire rod issue. However, one of the most noticeable signs of tie rods going bad will be a knocking sound coming from the front end of the vehicle when you turn into a parking space, or some other low speed, tight turning situation. The tie rod ends can be replaced separately, although we recommend you replace all of them at once. In addition, there is a connecting sleeve that connects both inner and outer tie rods together and also allows the distance between the two to change for your toe adjustment. Due to rust and corrosion on the tie rod threads, it is very difficult to break the rust free and thread out the individual tie rods. The procedure to replace the front tie rod ends is the same for both the left and right sides. Tie rod ends can either be right hand threaded or left hand threaded. Make sure you know which one you are looking to replace. Refer to the article on Tie Rod Replacement.

Stabilizer Bars: The stabilizer bars are also known as sway bars, anti-roll bars or some folks call them torsion bars.
Figure 2

Stabilizer Bars: The stabilizer bars are also known as sway bars, anti-roll bars or some folks call them torsion bars. Many consider torsion bars to act like a spring on each wheel. They are used on some vehicles instead of a coil spring or a leaf spring. They set the vehicle ride height by spring loading each wheel. The torsion bars support the weight of the vehicle like the coil spring on a coil-over. Sway bars don't support the weight but instead are a connecting link between the two sides of the suspension on a vehicle. The left side compresses the sway bar while trying to compress the right side at the same time. The sway bars are totally different. You can have no anti roll bar or you can have one per axle (sports cars have one at the front, and one at the rear). They resist the left and right sides being at different heights so that as the vehicle corners, it does not tip. For example, if you are turning left, your right wheels want to compress, and your left wheels want to lift, which causes the car to roll. The sway bar or anti-roll bar greatly limits this action causing the car to not roll during cornering, improving handling which you want in a sports car, or a truck or SUV. In a real off road vehicle, these vehicles typically don't have sway bars. Crawling over obstacles, the wheels will need to move to different ride heights without such interference. The sway bar connects the two struts of opposite sides of the wheels together creating firm steering. As you enter a turn the steering on the car moves the suspension into the turn. Inertia wants to propel the body of the car to continue along the straight path. This inertia coupled with centrifugal force throws the weight of the car towards the outside of the turn. This compresses the outside suspension with more weight on it and extends the suspension on the inside of the turn with less weight on it. This is known as body roll, and most drivers don't like it. The feeling for the driver is one of floating through a turn and not properly feeling the road. The role of the sway bar is to transfer the suspension compression on the outside to the suspension on the inside of the turn. Now a sway bar is made of metal and does flex so not all of the suspension compression is transferred to the inside wheels.  The sway bar does have its limits. Generally, a small sway bar will allow for more body roll and a larger sway bar will allow for less body roll. When sway bar bushings go bad they let the sway bar move around too much to be effective. The bushing may also squeak as you drive over bumps. If you discover that your sway bar bushings have failed, refer to the tech article on the steps to replace your sway bar bushings.

Drop Link: The drop link connects the sway bar to the connecting arm.
Figure 3

Drop Link: The drop link connects the sway bar to the connecting arm. The bushings act to cushion the response. If you are starting to hear a knock sound or the suspension feels loose when you go around a corner there is a good chance your drop link bushings are starting to go bad. These bushings get a lot of wear and tear and can see a lot of oil from the engine as the car ages. They do wear out and should be checked every 20,000 miles. If you are going to be replacing these bushings, it is a good idea to completely drop the bar and clean and paint it while you are performing the work.

Center Link: As you turn your steering wheel, a steering column shaft rotates in the steering column.
Figure 4

Center Link: As you turn your steering wheel, a steering column shaft rotates in the steering column. At the other end of the steering column is the power steering gearbox. This power steering gearbox changes the rotating motion of the steering column shaft into a side-to-side movement of the Pitman Arm. The Pitman Arm is connected to a center link. This center link connects the left side of the tie rod ends to the right side tie rod ends. This maintains the alignment of the left and right side wheels during turning maneuvers. The center link has ball joints on the end of it to flex with steering inputs. Over time the ball sockets can wear out. This allows the inner and outer tie rod ends to move around and allows small deviations in front wheel alignment. This can cause handling problems, steering wheel vibrations and uneven tire wear. Refer to the article on the steps to remove and replace the center link.

Pitman Arm: The Pitman Arms connect to the steering gear on a recirculating-ball steering system and transmits the force from there to the center (drag) link.
Figure 5

Pitman Arm: The Pitman Arms connect to the steering gear on a recirculating-ball steering system and transmits the force from there to the center (drag) link. They connect by way of the ball joints and also support the center (drag) link. The Pitman Arm does not have many parts. It is a sturdy part of the steering system. Some common problems include rusting, and a compromise of the plain bearing that connects the center link can wear out. When the ball joint wears out, steering can become loose and will continually deteriorate until it needs to be replaced. You will want to replace both Pitman Arms. Refer to the technical article on how to remove and replace the Pitman Arm.

Drag Link: The drag link connects the Pitman Arm to the steering arm.
Figure 6

Drag Link: The drag link connects the Pitman Arm to the steering arm. Unlike a center link, the drag link does not connect to an idler arm and has no inner tie rod ends attached to it. When the bushings begin to wear you may feel a shudder or looseness in steering. Refer to the article on the steps involved in changing your drag link.

Idler Arm: It is the job of the idler arm to hold the right side of the center link and inner tie rod for the right side.
Figure 7

Idler Arm: It is the job of the idler arm to hold the right side of the center link and inner tie rod for the right side. This keeps the left and right wheels in proper alignment while turning the steering wheel from left to right. Mercedes Benz uses a frame mounted bushing to act as the idler arm. When you service this part you will not be replacing the idler arm but the idler arm bushings. In order to do that you will have to disassemble the idler arm assembly. Over time these bushings can wear out and allow the right side center link and inner tie rod end to be slightly out of alignment with the steering linkage on the left side of the vehicle. This will cause steering wheel vibration, a knocking noise when changing direction and uneven tire wear. Refer to the article on how to remove and replace the idler arm.

Steering Dampener: As the suspension moves up and down and the car hits bumps the steering linkages absorb the shock and jolts of the suspension movement.
Figure 8

Steering Dampener: As the suspension moves up and down and the car hits bumps the steering linkages absorb the shock and jolts of the suspension movement. In an effort to suppress the shocks and jolts of the suspension, Mercedes Benz uses a steering dampener between the chassis sub-frame and the center link. It does this by slowing down the movement of the steering center link. The steering dampener is like a shock absorber for the steering center link, and this helps add to steering stability particularly while the car corners over a series of bumps. Refer to the article on how to remove and replace the steering dampener.

Steering Knuckle: Steering knuckles (red arrow) connect the tie rods, shocks and control arms to the wheels and brakes.
Figure 9

Steering Knuckle: Steering knuckles (red arrow) 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. Refer to the article on how to remove and replace the steering knuckle.

Control Arms: 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.
Figure 10

Control Arms: 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 (red arrow) 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. The ball joints are built into the control arms. In order to replace the ball joint, you will have to replace the control arm. Refer to the article on removing and replacing the control arm.

Front Spring: There are two front springs located on either side of your car.
Figure 11

Front Spring: There are two front springs located on either side of your car. These provide the major force disruption when going over bumps as well as reducing road vibration while traveling at speed. It is rare that springs will break but it has been known to happen. Visual inspection is in order to identify cracks or fissures. One technique is to spray the springs with water or penetrating oil and look for areas that are no longer smooth or for cracks. The fluid will act to highlight problem areas. If you have to replace a spring, use care and the proper spring compression tools.

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