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SL-C Manual: Suspension

Hardware

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The suspension is pre-assembled on the chassis for shipping purposes only. It is explicitly not ready to “just tighten up the bolts and go”. It is the responsibility of each individual owner to check assembly and evaluate all fasteners, spacers, washer and related hardware for their intended use. All fasteners must be tightened to their correct torque setting by the owner- the factory did not do this. You are responsible for the proper selection and assembly of all fasteners on the car. A guide to torque settings is in “General Information” section. Use washers and the appropriate fastener locking technology (safety wire, Nylocs, Stage 8 locks, etc.) for every fastener.

The button head cap screws that attach the front billet suspension mounting blocks into the chassis will need to be secured using Loctite. The photo below shows the location of these screws. In this picture, the recommended washers under the bolt heads have not yet been installed. Since regular washers may overlap into the openings, you may want to modify a normal washer to fit the open space. This can be done by grinding the edge of the washer, or by bending the edge of the washer in the arm opening. This helps prevent the washer from rotating.

Also, note the aluminum spacers inside the box. Be sure to keep these in place as they locate the rod end for the lower control arm.

The front and rear upper arms are attached to the chassis using ½ UNF grade 8 bolts.The rear lower arms are attached to the chassis using 5/8” UNF grade 8 bolts.The front lower arms are attached to the chassis using 5/8” shoulder bolts. Note that the 5/8” shoulder bolts feature a ½” UNC thread. The shock absorber upper mount points including bell crank to shock attachment and push rod to bell crank attachment are all ½” UNF bolts.

Rod Ends

It is critical that you ensure that minimum thread engagement length is adhered to for each rod end. Most texts recommendation for the minimum requirements for threading into steel is 1 times the diameter of the bolt (or rod end shaft in this example). For threading into aluminum it is safer to use 1.5 times the diameter. The SL-C uses mostly ½” diameter rod ends. So as an example you would want the rod ends to thread into the steel push rods at least ½”. Similarly, rod ends should thread into aluminum suspension arms at least ¾”. 

One way to verify this engagement policy is to paint a small mark in the threaded portion of the rod end at the point representing minimum thread engagement. You can then verify proper thread engagement by just looking at the exposed thread and making sure that mark is not visible.

If you are racing the car, some sanctioning bodies require a minimum amount of thread engagement. You are responsible for meeting whatever rules are in force for your car. 

The photo below shows the rod end thread engagement locations in the front upper suspension arms.

The photo below depicts the areas of the rear suspension where clearance is very tight when the suspension is at full droop (e.g. when jacked off the ground). These are where the bottom of the shock housing is fitted into the bell crank (top arrow in photo) and where the pushrod runs behind the top suspension arm. At full droop there is only 1mm or so of clearance.

If you are removing the suspension arms from the chassis at any time, please ensure the correct orientation of the aluminum safety washers. The safety washers are installed with the small diameter toward the rod end or bearing on shocks. The safety washers are different thickness at some suspension mounting points, in particular the lower front suspension attachment points. Therefore be careful to note their location so that each one goes back where it belongs. Front and Rear shock attachment points use a thin safety washer.

At the rear the safety washers are used in a number of locations.

If after removing the suspension arms, you need to remove a rod end from its arm, you should record how far it is threaded into the arm. For example, you can count and record the number of exposed threads.

Bump Steer

Bump steer refers to a change in toe as the suspension moves through its range, from fully compressed to fully-extended. In general, all cars have some degree of it, and in general, the objective is to minimize any toe change due to suspension travel, as it has the effect of adding steering effect, which the drivers usually perceives as instability or unfavorable handling. It’s called “bump steer” because the effect of the wheel/tire combo hitting a bump can cause the car to act as if there had been steering input added by the driver (when of course, it was a change in toe from the suspension moving close to full compression from hitting a bump in the road). It’s not just bumps we are concerned about though, as just pitching a car into a turn will compress the suspension enough to have some effect on toe. That’s why it’s vital for good handling to correct, as far as possible, any toe changes that arise from suspension movement.

The SL-C is designed to have very little bump steer. To get this adjustment close, the tie rod should be parallel to the lower control arm when the car is at rest (with tires mounted, and a normal distribution of weight in the car which of course requires the car to be fully assembled). You can establish minimum bump steer with a varying washer stack, and when you have it right, create a spacer of the same length.

If you don’t feel comfortable adjusting bump steer, consult a professional chassis engineer, or check at a local race shop. The advice above (getting the tie rods parallel with the lower control arm) will get you very close, and the shop can take it rest of the way as needed. 

Front bump steer is adjusted by moving the mounting location of the outer steering rod end vertically where it attaches to the front upright. The photo below shows the location of this adjustment. 

Rear bump steer is adjusted at the point where the rear toe link attaches to the rear upright a shown in the following photograph. Add or subtract washers while running the suspension through its range, measuring the toe change at the brake disc. You’ll probably find an inexpensive dial indicator very useful here as the changes are relatively small (on the order of less than .125”). Changing the number of washers will change the angle of the tie rod, which will have an effect on toe as the suspension moves throughout its range. Once the correct angle of the tie rod has been established by adjusting the height of the washer stack, replace the washers with a fabricated spacer made from steel tube.

Note that the picture here shows an early car with the rear tire rods in single shear. Later cars have a different arrangement with the tie rod in double shear, but the process for adjusting bump steer is the same.

Toe Adjustment

“Toe” or “toe-in” is the term used to describe the angle of a pair of wheels on the same axle. Wheels that are exactly parallel to each other are said to have zero toe. Wheels that point inward (or “pigeon toed”, or are closer together at the front) are said to be “toed in”. Likewise, wheels that point outward are referred to as “toed out”.

Most cars will need a small amount of toe in on the front and rear to make the car feel more stable, especially under braking. Don’t vary much from the recommended settings unless you have substantial experience setting up race cars, as incorrect toe setting will make any car handle very erratically.

The normal toe adjustment settings are listed above in the General Dimensions section. 
Note that unlike many cars, the SL-C has adjustment for toe in both the front and the rear wheels. The rear toe link can be seen in the picture above; the red arrow points to the end connected to the upright. The other end is connected to the chassis. 

Adjust the rear toe by loosening the lock nuts on each end and turning the link so that the effective length is either shorter or longer, depending on which direction the toe needs to move.

To adjust the front toe, do the same with the tie rods on the steering rack, as shown on the picture below:

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Note that like many suspension settings, toe, camber, caster, bump steer and other settings are all interdependent, and changing one may change another. When setting the suspension up, leave it to a professional, or be sure to check that, for example, what you have done to fix the toe didn’t alter the camber, or bump steer, etc. Unless you have experience aligning suspensions, just get the settings close enough to get the car to an alignment shop. Once the alignment is finished, mark the adjustment nuts and bolts positions with a paint stripe so if necessary you can restore them to their original positions. 

Ball Joints

Check to see that the bolts attaching the front ball joints on to the ends of the suspension arms are installed with the bolt head toward the inside surface of the wheel. The rear ball joints should be installed with the bolt heads facing down, opposite to the fronts. Trim the bolt to the correct length if clearance is needed. 

This ensures the maximum possible clearance between the wheel and the ball joint mounting fasteners. 

Also, be sure to use washers wherever a bolt or nut contacts aluminum, especially in the suspension. Failure to do so will result in galling of the aluminum, especially as the fastener rotates during installation and removal and may allow the fastener to loosen over time.

Also, be sure to verify the edge of the ball joint does not contact the rotor or other brake parts. Ball joints are a part made by many manufacturers, and tolerances-- and even flange designs-- can vary, so check yours. In the picture above you can see the builder had to grind the outer edge of the ball joint flange to ensure adequate clearance from the brake rotor. According to one builder, MOOG K-6136 is a replacement ball joint that fits perfectly and does not require any grinding to clear the brake rotor.

When installing the ball joints, be sure that the castle nut threads onto the stud such that the cotter pin can engage the notches in the nut properly. The picture below shows a stack of washers needed to bring the nut to that height. The washers can be used to establish an optimum height, and then ideally are replaced with a solid spacer of that thickness. If you choose to use the washer stack itself, consider taping them together around their periphery so when removed they will remain as a stack and the correct height will be maintained.

Be sure to use the cotter pin, as shown in this photo, to prevent the Castle nut from loosening.

 

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When torqueing the castle nut – or for that matter any fastener – if the fastener does not hold the torque, disassemble the fastener and find out why. Replace and destroy any fastener, including ball joints, that have mangled threads, do not hold torque or in any other way do not work correctly. 

When installing the ball joints, be sure to check that each joint has a Zerk fitting, and that you grease the joint before putting the car in service. If you need to add or replace a ball joint Zerk fitting, they can be obtained at most parts stores, local or online. Note that some cars have been shipped without a Zerk or a cap to close off the interior of the joint. Failure to seal this opening will cause increased wear, strange noises (when dirt gets inside the joint and increases clearances) and unusual handling characteristics. The front ball joints use a 1/4-28 Zerk fitting, available from McMaster or your local parts store.

Failing ball joints have also been identified as a source of hard steering, so if you feel the effort is too high, check to see if your font ball joints have been adequately greased. If they are worn, they are inexpensive to replace with new ones.

For those tracking or racing their cars, there is a track kit that can be used to replace the ball joints with competition-quality rod ends. For race-only applications, there is a specific upgrade that allows very fast camber adjustments, race-quality bearings and rod ends instead of ball joints. These are normally unsuitable for the street as they reduce the available steering angle. Please call the factory for more details.