The SL-C has arguably the most advanced suspension system on any component car.  From double-adjustable shocks, and elimination of soft rubber bushings that rob road feel, to the selection of billet aluminum as the material for all suspension control arms, the evident quality of design and execution is there for all to see.

That doesn't mean that you, as the builder, don't have to assemble and setup the suspension to get the most from it.  Improper assembly can have effects ranging from inability to get alignment in specification, to the pieces falling off the car.

It's critical to look over every suspension component on the car before you drive it, and be sure it is assembled correctly.  Some of the things to consider are an adequate number of threads engaged in every fastener, especially rod ends, and the use of safety wire, Loctite, safety washers and other methods by which the assembler is assured that the fasteners stay fastened. 

If you aren't an experienced race mechanic or fabricator (and most of us are not), please get a copy of Carroll Smiths series of books on fasteners  here at Amazon: http://www.amazon.com/Fasteners-Plumbing-Handbook-Motorbooks-Workshop/dp/0879384069/ref=sr_1_1?ie=UTF8&qid=1394720978&sr=8-1&keywords=carroll+smith%27s+nuts+bolts+fasteners+and+plumbing+handbook

Suspension Fasteners

Check the fasteners on the car. The car is assembled at the factory just enough to get the car able to roll, to facilitate loading. That means that sometimes bolts that are not final may have been used. Some of the issues are bolts that are all-thread (that is, bolts that don't have a shank, but are threaded to the bottom of the bolt head), and bolts that are too short or too long.

The problem with all-thread bolts is that the threads, exposed to a rotating object like suspension bushings, tend to act like a cutting tool, elongating the hole. Thus, you should be careful to use bolts that have precisely the correct grip length. Never use all-thread bolts in suspension applications.

 Bolts that are toolong or too short should also be replaced.  Use Grade 8 bolts, washers and nuts. Also, when buying Grade 8 hardware, beware of counterfeit product.  As far back as 1993, counterfeit bolts were recognized as an issue. See this PDF for more details on how to recognize the real from the wannabes.

Finally, see the Fasteners page for more info.

Ball Joints

The ball joints onthe SL-C are designed for strength and user replaceability. However, some joints may have improper nuts on them. The standard ball joint uses a 1/2" stud.  However, some may have had metric nuts assembled on them incorrectly. The metric nuts typically won't hold torque, and don't feel right when you tighten them.

The Tip: remove all nuts on all ball joints to validate that the nut and the stud have the correct threads. Replace as needed. Most of these use spacers to get the castle nut at the correct height. Be sure to use good quality--grade 8 if possible, or NAS washers if you are bucks up- or consider making spacers from solid rod of the right diameter, drilled to allow the stud to come through.

If you are tracking your car, be sure that you life out ball joints-- and all other wear items in the suspension.  The ball joints should be replaced after 20 hours of track time, or less if you regularly use the curbs.  In  fact, the factory offers an upgrade to the regular suspension ball joints that replaces them with spherical bearings for added strength and life under the extreme duty that track days provide.

Ball Joints and track/race cars

The ball joints provided are very strong, and as is usual with Superlite products, engineered with a large safety margin.  Because they are originally specced for a full-size pickup, they are more than adequate for normal street use in a car that weighs a fraction of the vehicle for which they were originally designed.

However, there have been a couple of failures on track cars that have been using the stock ball joints.  This can be avoided by lifing out the ball joints.  There are also some upgrade options.

Here is a table with the essential options for ball joints:

Application  Recommendation  Pros  Cons 
Street  Use the stock ball joints, or consider the upgraded race ball joints. Inexpensive, already there, good safety margin for street use, the stock joints are "free" and proven to be fine on the street.  A race joint is a cheap upgrade if you want to add more safety margin.  None, really, but like all wear items, either ball joint should be lifed out, especially if your car sees extreme duty (rough roads, high power, etc) 
Track  Upgraded race ball joints, or new track ball joint replacement kit from Superlite.  Occasional track use: race joints, heavy track use, upgraded spherical kit from Superlite. 

The race joints are inexpensive, and are built to higher tolerances.  


The replacement kit dispenses with the joint entirely and replaces it with a CNC aluminum cup, and spherical bearings. 

The race joints are under $100 or so each, but the upgraded spherical bearings kit are around $1200.   With heavy track use, you still need to monitor the wear of either of these options.  


The spherical bearings restrict suspension travel and steering wheel cut angle, so these are not suitable for the street.

Race  Complete race suspension from Superlite.  This is an expensive upgrade but includes new uprights, new lighter arms, replacement of the joints with  spherical bearings, and allows camber adjustment with shims for quick changes at the track. Same geometry as the stock suspension, but more rugged, suitable for race applications. The most expensive option, but the proper choice for a race car.  Like the track upgrade, these also restrict turning angle and suspension travel, so are not suitable for the street.  Like all race parts, periodic inspection of the bearings is required, and lifing them out is a good idea as well.

In terms of ball joints (as opposed to the track and race setups which use rod ends) the race ball joints listed in the chart below are a heavier duty version of the original GM pickup upper joint.  

The chart below shows several vendors of alternate and occasionally heavy-duty ball joints and their part numbers. Note that the SL-C is designed for 19" rear wheels or greater. If you are using the CCW 18" wheels in the rear, there may be clearance issues with some of the aftermarket ball joints. One builder with 18" rear CCW wheels found that there was interference with the ball joint and the wheel when he installed the QA1 joints listed below. Depending on your car, you may be able to grind the ball joint for clearance, or failing that, use another one.

If you are using 18" rear wheels, be aware of the tight clearances in this area, and do a dry fitup before you install these permanently so they can be returned if there is a fitment problem. Most cars that have at least a 19" rear wheel won't have a clearance problem, as this is normally only an issue with 18" wheels in the rear. But check clearances, both static and dynamic to be sure. Dynamic clearance can be checked by using clay on the inside of the wheel rim, followed by careful driving, then checking any "machining" of the clay.

Note that there may be considerable variation in installed height and features in replacement joints that have the same interchange.

We recently did a small ball joint analysis and this is what we found:

The QA1 1210-103 listed in the chart actually has a pintle (the part that comes out of the socket and is bolted to the lower part of the upright- QA1 calls it a "stud") that is too short- installing it will cause the upright to bind against the ball joint in turns. You can replace that pintle with a longer one from QA1, but it is a little taller than the stock one. This joint will result in control arms that are spread about .250 wider than the stock joints, which looks like it would slightly increase the amount of negative camber gain in compression, as well as a small change in roll center.

The QA1 ball joint is a very nice piece, apparently made from billet steel, and with the very best feel. It is completely adjustable for feel, as well as being rebuildable. But QA1 says it isn't for street use, and in fact, comes with no rubber seal (presumably you have to re-use the one from the ball joint you are replacing). If you treat it like the wear item it is, and check it frequently for wear, it's probably great for the street when you use it with an adequate rubber seal (the seal from the original factory ball joint fits fine over the QA1 joint body). The part comes with no hardware except the castle nut. You have to buy both QA1 tools (the spanner wrench and the hex key) to properly assemble or rebuilt the ball joints, so factor that into your calculations.

You can order the correct QA1 joint with the longer pintle/stud using part number 1210-203B. The "B" suffix denotes the longer stud, and using this part obviates the need to replace the stock stud with the longer one. If you order the 1210-103 joint, you'll need to order the correct pintle, which is 9029-203. These joints are available from the usual suspects including Jegs and Summit.

The Moog K6136 that this writer evaluated was made in the USA, but had a fair amount of resistance, a rough feel to it, and tended to bind in certain parts of it's range. Perhaps it would wear in with miles on it, but it actually felt like it had more resistance than a slightly worn OE joint. On the other hand, the Moog had a superior design for the included rubber seal, and also included a complete hardware bag with all new attachment bolts and nuts, a new castle nut and the required cotter pin. Importantly, the Moog also had a pintle that was longer, like the QA1, so it has the same installation problems (see below for a solution to the too-long pintle). Based on measurements taken by a couple of builders, you may find the Moog joints to have a pintle or stud somewhere between 3/32" and 1/4" longer. Measure yours to understand what the difference, if any, is on your car.

Finally, an older joint that had been in service on a street SLC was removed and examined. Initially it seemed too tight and a little balky, but new grease and a little time working it in improved the feel noticeably. That probably shows the sensitivity to proper greasing that these parts require. The Pro Tip: Grease your ball joints with good grease before you drive the car at all, and check, and grease them frequently.

The takeaway: for most people with street cars that don't see track duty, the original ball joint from Superlite is the way to go. It fits as intended, works quite well when properly lubricated, and is cheap to replace.

Make sure you measure carefully before you put in any new joint to check the installed height on the upright not just the overall height, as subtly different shaped studs will influence installed height dramatically. For those cars that see occasional track duty and want to keep the ball joints (as opposed to the upgrade available from the factory), the aftermarket joints can be a solution, but be aware of the compromises (slightly different geometry with a taller pintle, increased cost, possibly new tools, the possible need for spacers, and the requirement to possibly source hardware and seals in some cases, as well as the requirement to use a different pintle with the QA1s).

For those using the QA or Moog joints that are a little different dimensionally, the suspension geometry changes as noted above if used without changes. One builder has made up spacers that make up most all of the difference in installed heights for the QA1 joints. These are installed under the ball joint to lower it slightly to get very close to the stock height. There is a CAD file available; contact the wiki admins to discuss getting it if you want to have the needed spacers made up for your car. A limited number of spacers from .250 aluminum are available if you just want to buy spacers that are already made- please contact the wiki admins if you want to buy a set.


(From Wayne Marov)

For those that are new to building or unsure what to do, I thought I would save you some time. Remember, these cars are put together to just roll into a trailer. I am not criticizing or picking things apart I am just sharing my experiences and what I did about it.  I am at the stage where I wanted to complete the suspension, one corner at a time and these are some of the things I came across.


1. Ball Joint spacers: In order to get the cotter pin hole in ball joint shaft to align with castle nut, spacers are required. Mine had two shims and an aluminum safety washer. Not good. If you torque a castle nut (79ft/lbs) over an aluminum washer it will gouge it. I took it apart to measure the thickness required and made one steel spacer. I happen to have a lathe and had a piece of 1-1/4" solid steel round bar that I bored a 1/2" hole through about 2 or 3 inches then cut 4 pieces .426" (one for each ball joint). Painted them black. I feel a lot safer. Good luck trying to torque the rear ones, I hope you can guess accurately (with an open end wrench).

2. While the castle nuts were off, I separated the ball joint from the upright. I did this for a couple of reasons, first, on the bottom of the upright there is a steel plate with four socket head cap screws. I removed each one to put thread sealant (steel bolt into alum) and torque. I check every bolt on the car for thread sealant and torque. Secondly, I put washers under the four grade 8 bolt heads holding the ball joint bracket to the lower control arm. Also, on the two bolt heads to the lower shock mount to lower control arm. I have always believed in protecting the softer aluminum from the hardened steel bolts. I did a thorough check of the entire car and found several areas that need washers. I sometimes find that using a metric washer on SAE Bolts will provide less slope on bolt shank and also a little smaller outer diameter for neater appearance. 

3. The rear toe link spacers: Mine had eight yes 8 large thick shims. I made the same steel spacers using 1" round bar with a 1/2" hole through a few inches and cut two pieces .807". Don't forget the washer on the bolt head. For the bracket attached to the rear upright I received them with two washers and just left them. I am not a machinist and don't aspire to be one, and it does take time to make these. Ask a local shop to make four of one size and two of another and see what he wants to make them. I know what a PITA it is to constantly ask a shop to make me one of this and one of that. If enough guys need/want them I could buy a long piece of round bar, bore one long hole and cut several spacers from that piece. Now, I don't care to do that, and won't, but I have a friend who is a retired machinist that would charge a very reasonable rate to do this at my shop. I'm not selling it, but if it can help out let me know. Some guys may need spacers for the street tail hinges.

4. While all four hubs were off, I scuffed them up a painted them black. They are steel and had already had surface rust on. I happen to have a borrowed set of CCW's wheels on the car (thanks Jack) and noticed that the rear wheel studs are not long enough. So while the hubs were off, I pressed in new ARP wheel studs. 


5. Don't forget washers on the caliper bolts. 

6. Something I have always done, is to mark each bolt with bright red marking pen when they are properly torqued. When they are torque checked later, I put a second mark.

7. So far there have been 44 shims removed (see picture to right) and I have about 10 more temporarily keeping my rear clip aligned.


Helper Springs

The Problem

Helper, or Zero-rate springs, are sometimes used to keep a coilover stack aligned when in full droop.  In other words, when you jack the car up and the wheel is off the ground, in some cases the spring and the perch will become mis-aligned, so when the car is dropped back on the suspension, the spring is no longer concentric with the perch.  This plays havoc with alignment.  :)

The solution

Use a helper spring from Pegasus (part number 1876-4) and the correct collar to tie the helper spring to the suspension spring.

The collar can be obtained from Amazon, or other sources.  Use Genesis 2.5" spring guide (if you are using the standard 2.5" springs) available from HRP, or from Amazon.

Here's a link to another builder's approach to helper springs.

Rear Springs

The factory rear spring are normally 650 lbs/in.  If you have a heavy transaxle, a dry sump and a big engine, you may need stiffer springs.  Consider going up 100 lbs to a 750  or 800 lb spring.  Springs vary, and if after examination you think your springs may be in danger of coil bind, replace them with a stiffer one.  You can also use an 8" spring to get more length, which may be useful.

Springs can be obtained from the usual sources like Jegs, Summit and Pegasys.  The factory has supplied QA1 springs, and lately, Swift springs.  Other good names include Hyperco and Eibach.  Check their catalogs and distributors.  Springs are easy to change, and can make a big difference in the way the car handles, so feel free to experiment, knowing that the factory springs represent a pretty good start.

Front Springs

 The default factory spring rate for the fronts is 600 lbs/in.  you can use 7 or 8 inch springs.  If you are planning to use the RamLift- which most street cars will find very useful- you need to source 4" springs.  Hyperco has them in 600 lbs, which is where you should start. 

Suspension Life

As more SL-Cs get miles on them, it's a reasonable thing to ask how long the suspension pieces will last before a rebuild is needed. All street cars eventually wear out bushings in the suspension, and so it shouldn't be a surprise that the SL-C, if driven enough miles, should experience wear as well.

Like production and race cars, the SL-C never really needs maintenance on the billet suspension pieces- these normally last the life of the car, absent abuse or accident damage. But bearings (including rod ends), which are the equivalent of the rubber bushings in "normal" cars, do wear out, and will need to be replaced.

It's hard to know how long bearing should last, but one builder got 15,000 miles on his car before he saw worn bearing and rod ends. While many SL-Cs will never see that kind of mileage, that is probably really good wear for what is essentially a race suspension on the street.

In fact, all pro race teams establish a replacement schedule for suspension rod ends and the bearings in the suspension. For the SL-C with the standard suspension that sees mostly street duty, here's a very conservative suggested schedule:

 Rod ends: Replace with quality Aurora bearings every 3 years or 4000 miles.

 Bell crank bearings: Replace every 4 years or 7000 miles, more often in severe duty like track days or crashing over potholes on the street.

 Ball joints: Replace every 3 years or 4000 miles for street cars, every 20 hours for track cars (or replace with the upgraded parts from Superlite as discussed above if you are tracking the car). Note that the race cars don't have ball joints- they are replaced with rod ends.

This is just a suggestion- cars have gone well beyond these time and mileage suggestions, but this is pretty safe. Remember, this is a race car for the street (or track, or race).

If you have the race suspension on a race-focused SL-C, it's good practice to examine all bearings, rod ends, etc after each event, and inspect and replace if needed each season. 

Replacement Parts

Worn rod ends, bearings, etc can always be sourced from Superlite. This is easiest, unless you are very sure you know what exactly to order. If you are sure, here is a link to the QA1 page where one of their rod end lines is displayed.

One builder notes that the rod ends on the rear suspension bellcrank is a QA1 PCML-8.

Here is a link to the Aurora flipbook of the rod ends.