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Upgrading Our Street Stock Suspension. Part 2: The Rear End

The front suspension was dialed in and ready to go, but our bomber stock Camaro was ready for some serious AFCO Racing help in the rear.  Past experiences had left us wanting more.  Our driver was finally getting into the corners hard enough to move the rear end around in the chassis, and we were experiencing incomplete races due to extreme parts failures like bent shocks.  Our friends at AFCO Racing assured us that we were going to be alright.  Leaf spring chassis have been around for years and AFCO had the experience to help us fix the problems.  We set our goals with this project car to install and tune our leaf springs for victory lane.  After this, it was all going to be on the driver to get us there.

Our project car was in some serious need of suspension help with smaller, worn out leaf springs that allowed excessive axle wrap and side to side movement of the rear end. We put in an emergency call to AFCO Racing.

Our AFCO Parts List For The Rear Suspension:

(1) Right Rear Leaf 176 (part # 20228)

(1) Left Rear Leaf 205 with Wrap Up Reinforcement (part # 20228HDRF)

(2) Stock Shackles (part # 20236-2)

(4) 9 1/2″ Plated U Bolts (part # 20238-9)

(2) 3 Position Spring Plates (part # 20250B)

(2) 2″ Lowering Blocks  (part # 20248)

(2) 1 1/2″ Lowering Blocks (part # 20247)

(1) 1/2″ Lowering Block (part #20244)

We talked with Ben Baker, AFCO Racing’s dirt circle track specialist about our project platform; A 1978 non-metric chassis Camaro.  Baker was familiar with this type of suspension because almost every track that has a street stock division features a parade of these Camaros in every race.  With a little information on the track and normal racing conditions, Baker was able to guide us to a set of leaf springs that would prove to be more than just a good starting place.  While the leaf spring suspension may seem like a simple system with only two leaf springs, a couple sets of shackles and a couple sets of bushings, but there is more to the leaf spring setup than its simplicity would indicate.

AFCO’s Ben Baker recommended these parts for our project car because they would bolt up to the stock mounting positions “with no real issues.”  Baker also recommended the different height lowering blocks “to help get the proper ride height and wedge settings.  Low friction bushings in the front eyes of the leaf springs are fine to use with no issues but you should make Delron bushings for the rear eyes of the springs and the rear chassis bushings.”  Baker ended up by warning “Make sure when you bolt the springs on to us nylock locking nuts and do not over tighten the springs. If you over tighten the springs it will cause the suspension to bind.”

AFCO Racing offers leaf springs for dirt track Camaros in various rates. Our old worn out puny leaf spring at the top looks humble compared to the new AFCO Leafs.

AFCO offers leaf springs in several different spring rates for the Camaro in the dirt track market.  By design, AFCO adds more material to the front part of the Camaro leaf springs to make them act more like Chrysler type asymmetrical design with a shorter and more stout front section.  This helps provide traction under acceleration without wheel hop.  For the 3/8 mile semi banked oval track with decent traction, Baker set us up with a 176 rated spring on the right rear (part number 20228).  The left rear required a little bit more for our track with tight corners, so Baker recommended a 205 leaf spring with wrap up reinforcement (part number 20228HDRF).  According to Baker, the AFCO Leaf Springs are made from Chrom-vanadium and are set to precisely the blueprinted specs for arch and length.  Chrom-vanadium steel is manufactured with a chromium content somewhere near 1 % and when heat treated has excellent  strength & toughness properties;  it is also resistant to fatigue.  Chrom-vanadium with high carbon content is used to make ball bearings and roller bearings, so that tells us that the material is a great choice for high stress applications.

AFCO Racing's leaf springs are manufactured with Chrom-vanadium steel for reliability and durabillity.

The minimum tensile strength of chrome vanadium is particularly high compared to other alloys.  When coupled together with the stronger front area and the heat treatment process, these springs have an extended period of life which is perfect for budget race teams looking for long term performance.  The final process for the leaf springs is a shot-peening stage that relieves stress in the steel.  Steel cools at different levels, which causes the steel to form layers, much like the rings inside a tree.  Shot peening lessens the stress from these cooling layers and provides a more durable and longer lasting leaf spring.

Installing and Tuning leaf springs requires checking to make sure that leaf springs are not twisted by poor mounting.

Installing and Tuning Leaf Springs

According to Eric Saffell, Product Manager at AFCO, “Leaf springs produce consistent performance when the installation factors are taken into consideration during the spring installation.  They can also produce a stiffer or softer rate than measured at the factory, depending on the installation.  For example, where the axle pad makes contact with the leaf spring, it deadens that part of the leaf spring.  Depending on the size of the mounting pad, the increase in spring stiffness is proportional to the amount of the spring that is deadened by the mount.  Stock axle pads have a rubber lining that does little to deaden the pad.  When racers change over to solid axle mounts and lower plates, more of the spring gets deadened and an increase in spring stiffness takes place.

Twisting the leaf spring can also cause increase spring rate over the manufactured and advertised rate.  The increased spring rate is directly proportional to the amount of twist in the leaf spring.  Twisting in the leaf spring is more common than most racers realize and can be caused by stagger, wedge, bent axle tubes, race damage repair and misaligned chassis mounts or axle tube pad mounts.  The leaf spring will twist whenever it is tightened to a surface that is not parallel to the axle mount.

Shimming and angle milling the axle mounts or using lowering blocks can be done to minimize the amount of leaf twist.  Angling the leaf and shackle mounts can also be utilized for the same purpose.  Leaf spring twist is more likely with solid type leaf spring bushings than with pliable rubber bushings.  Whenever the rules allow, Saffell recommends using AFCO’s front eye pivot type bushing, which eliminates leaf spring twist from body roll and misalignment.

In addition to leaf spring twist, the leaf spring static tension should be checked for parallel mounting from a side view at ride height.  Static tension will also cause an increase in spring rate.  Using a clamp on axle bracket will help eliminate any static tension or misalignment conditions.

Shackle angle can stiffen or soften the spring rate. When installing the shackles, the best starting place is at a neutral 90 degrees.

SHACKLES

The angle of the shackle can stiffen or soften a spring’s normal rate. The effective rate of a leaf spring is increased by decreasing the angle of the shackle.  The reverse is also true; increasing the shackle angle decreases the spring rate.  The length of the shackle affects how quickly the shackle will change it’s angle.  A shorter shackle will change it’s angle quicker than a longer shackle when the leaf spring is deflected.  Baker recommends using a shackle that is two inches longer than stock on this type chassis whenever the rules allow.  Unfortunately for us, our rules dictated using stock components.

ARCH

The free arch of a leaf spring is correctly measured by drawing a straight line through each leaf eye center and then measuring from the line to the spring surface at the centering pin.  The spring should be lying on its side in the free state whenever it is measured. Experimenting with different arches can help you by changing the effects on handling.  A leaf spring with more arch will raise the chassis and the roll center.  The effect of raising the roll center will mean that there will be less chassis roll and less rear side bite.  Increasing the leaf spring arch on the left rear will increase the wedge and make the chassis tighter off of the corners.  Decreasing the spring arch would have the opposite effect.

Lowering Blocks can help dial in the chassis setup by moving the chassis roll height up, but they can also create a problem if the leafs are not mounted flush to the axle mounts.

LOWERING BLOCKS

Our parts list included several different sized lowering blocks.  These blocks are generally used to change the ride height of the chassis but can also be used to adjust wedge.  The addition of lowering blocks will lower the chassis which produces less roll steer which will help the chassis to turn.  However, if the lowering blocks drop either or both spring eye positions relative to the axle then the rear roll center height will be lowered and chassis roll, along with rear side bite, will increase.  A lowering block that is too large can prevent the leaf springs from absorbing engine torque which can reduce forward bite.  A basic rule of thumb is not to exceed 4 1/2″ distance between the bottom of the axle tube and the top of the leaf spring.

We used AFCO's 1 1/2" lowering block to get get our wedge and ride height correct.

Shocks

The race track rules limited us on what we could do with the shocks by stating the the shocks had to be non-rebuildable.  For a starting point, Baker recommended we start with AFCO #1020 on the left front and an AFCO # 1021 on the right front.  For the rear stock replacement shocks Baker suggested AFCO’s #1032 on the right rear and left rear.  This initial set up would allow for a switch to AFCO #1034 on the right rear if the track started to turn dry slick or a switch to AFCO #1022 on the right front for more forward bite.  This set up would keep us to a 5 shock package that is perfect of a low dollar race team and helps minimize confusion on adjustments by keeping chassis shock tuning adjustments limited to two simple adjustments.

Getting the right shock coupled with the right leaf spring rate is key to a perfect race set up.

Set Up

Working with the guys at AFCO, we decided to set up our chassis initially with 50 pounds of wedge and 3″ of stagger.  According to Baker, our target weights for the initial scaling session should be 55% rear weight and 53% left side weight.  Most importantly, we were told to keep the rear wheels in line with the front wheels and leave the option of moving the right wheel inboard of the right front by two inches for extremely dry tracks.

Top Ten Installation Tips For Rear Suspensions:

  1. Installing the leaf springs is easier if you start by installing the front end first.
  2. With the leaf springs in place and the mounts secure, set the rear end on the leaf springs but leave the mounting pads and U-bolts loose enough to center the rear end.  Then put the weight of the car on the springs and set the pinion angle before welding the mount pads in place.
  3. Use U Bolts that are rated at a minimum of Grade 5.  For 1/2″ fine thread U Bolts, the standard torque is 50-55 foot pounds.
  4. Re-torque the U Bolts after the first night of racing and then every fourth race after that.
  5. Always start by squaring the rear end to the chassis centerline.
  6. Only use stock rubber front bushings with shoulders to prevent side loads if you are using the stock type bushings.
  7. Plastic washers can be used as shims to fill the gap between the spring bushings and mounting box on the chassis.
  8. Always check to ensure that the axle mounting pad is flat and square with each other and with the leaf spring.
  9. Always use new fasteners.  Old nuts and bolts can be weakened with age and abuse.
  10. Resist the urge to use pneumatic tools to tighten any of the hardware.

Using a two post lift and a differential jack made the installation very easy, but a floor jack and jack stands will work just as nicely.

Our Installation

We managed to install our AFCO rear suspension within a couple of hours, but we admit that having a two post lift and a rear end jack helped substantially.    With a hydraulic floor jack, a set of jack stands and common hand tools, a weekend warrior can perform this job in the same amount of time.  The toughest part of any suspension component installation project is always the removal of the old parts.  Pneumatic impact wrenches can be used to break the toughest fasteners loose.  Once all the old parts are removed you can begin installing the new parts.

It helps to lay the parts out on the ground in sequential order prior to the installation.  With our project car on the lift, we secured the fronts of both leaf springs to the chassis and positioned the rear end into place.  The shackles came next so that we had a mounting point for the rear of the leaf springs.  With the leaf springs secured to the chassis at both ends, we attached the U-bolts, spring/shock mounts and lowering blocks in position around the axle tube.  With the weight of the chassis on the leaf springs, we checked the shackles for twisting and the shackle angle.  With the rear end centered in the chassis and the shackles installed in a neutral position (neither forward or backward but straight down) and the pinion angle was checked.  We were looking for a negative 2 degree pinion angle and needed to roll the axle housing slightly to reach that setting, then we tightened down the U-Bolts.

Our red and white Camaro had no problems with the track conditions and could hold a tighter line through the corners. Here our driver makes a pass for the lead and his first heat race win. There's no doubt that the suspension upgrade helped.

Track Testing

We took the car out to the track on race day to see what kind of changes our suspension upgrade made.  The driver commented on the chassis feeling much more stable entering the corners and through mid corner but was loose coming out.  The track was on the dry side for the racing so we felt that we could correct the loose off condition with tire backspacing and air pressure.  For further proof that the suspension upgrade made that much difference, our driver took the car out for his heat race, starting from the absolute back of the pack and won the 8 lapper.  It was the driver’s first dirt track race win.  We left the track knowing that a good suspension and good setup will take an average car to the front of the pack.

Sources

AFCO Racing

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