A while back I had an oppourtunity to sit down with Steve McClenon the owner of Hotrods to Hell in Burbank, California. I spent a couple of hours chatting with him about his CenterDrive suspension systems. Finally I have found the time to put it down on paper and post it to the website. Enjoy.
HRHP: Why Truckarm?
STEVE:
In 1993 I had built a 38 Chevy Coupe for myself, with a very stout big block putting down around 575HP. I wanted this car to handle. The front was easy, mustang II with Chevy intermediate disk brakes. The rear suspension was a different story, 4 link was out of the question, the leaf springs were equally unacceptable, this car had to handle.
I was left with no readily available options. Having long been a fan of Grand National Stock Car racing (Winston Cup) I knew of Truckarm. I started researching the subject; I found the IROC cars also used it, as well as Busch (road course and oval). I soon discovered that there was no information available on the setup, and the Winston Cup chassis builders wouldn’t part with any information, most hung the phone up on me for asking. I gathered up what parts I thought that I would need then started figuring and drawing. I could see that this “simple�? suspension actually involved much more then meets the eye.
I continued to drive my leaf spring car as I researched, but a near death experience at 135 mph on the freeway changed that. The car took a bad hop off a bump and jerked over 3 lanes, I couldn’t lift all at once or the car would barrel roll so I had to squeeze out of the throttle slowly and drive out of trouble. I was able to collect the car inches from the center divider, still going about 90mph. I brought the car back into the fast lane and slowed down to normal freeway speeds. The next day I took the car to work, cleared a space and began to install Truckarm on the car. I looked at the process as a matter of self-preservation, and I had to start somewhere.
Soon the inaugural test drive, just pulling out of the driveway I could feel the difference. The car no longer creaked and groaned from chassis flex. I headed for my personal drag strip, the I-5 North onramp at Fletcher Drive. A long slightly uphill strait, with longitudinal expansion bumps at the top. With leaf springs the coupe would always get sideways. In first or second it wasn’t that big of a deal, but in third around 6000-6500rpm it would start hazing the rear tires and get sideways. This time I was able to flat foot it all the way onto the freeway. I could never do that before Truckarm no matter what line I took on the ramp. I was able to come up onto the freeway in fourth gear and the car just floated over the expansion bumps. The only distraction was the sheet metal blowing around on the car.
That moment was an epiphany for me. I knew that this deal worked, I knew why the cup boys had been using it for all these years, because it actually works. I knew that mistakes had been made, but the improvement to my 38 was nothing less then a total transformation.
This all happened over 11 years ago. We started building custom kits for our customers‚ car. Tri-Five Chevys, El Caminos, Chevelles, Novas, Camaros. Each time our customers were never less then ecstatic, as each car was transformed. As the years progressed we continued to develop and refine the system as each chassis has its own unique requirements. The next step was to develop kits that could be installed by the end user. The first kit was worked out for tri-fives, and 37-54 Chevy passenger cars, then Chevelles and it just kept on going.
HRHP: What came before Truckarm?
STEVE:
For all around live axle suspension Truckarm is the only viable option. A bold statement, I realize, but let us look at the requirements of a live axle rear suspension. Multi-tasking is a word that comes to mind.
Here is my list of priorities:
- Transmission of power to the ground
- Locate the rear axle in the car
- Isolate the chassis from surface irregularities (bumps)
Leaf springs are the cheapest and least effective way to get these three things done. Leaf Spring suspension was great for horse drawn wheeled vehicles when they only had to work as a spring.
The model A with transverse leafs used a wishbone in the rear for fore, aft, and rotational location, and power transmission. The leaf springs only had to do that job of a spring. On the model A the rear leaf only had to suspend that chassis and locate the axle laterally as the torque tube still provided rotational location and shared in the fore and aft location and power transmission
The parallel leaf soon appeared. At first a torque tube still provided rotational location and shared in the fore and aft location and power transmission, while the leaf springs did lateral location and suspension duties. The accountants at GM must have taken some engineering courses as the torque tube was eliminated. Now the leaf springs had to do everything. Suspend the car, transmit power, and locate the rear-end in the chassis. (Lateral, fore and aft, rotational, and transmit power to the chassis) Although this situation is far from desirable, it is cheap. Enter axle tramp (wheel hop) bump and roll steer, pinion wrap up, side sway, and as horsepower increased chassis twisting and sideways launches.
In 1958 Chevy came out with a 3-link setup to address the shortcomings of leaf springs. 2 lower and 1 upper link a short panhard and coil springs. One of the worst bump steering rear suspensions ever devised. The short links as they traveled through their arc would steer the ass end all over the place. The half-length panhard off on two planes added to the problem as its short length causes the rear-end to move laterally as the car moves up and down.
In 1964 Chevy introduced the triangulated 4-link on A-bodies. Gone was the panhard as it was replaced with triangulated upper links for rear-end lateral location. This setup was still plagued with the problem of short links traveling through sever arcs steering the rear-end in bump and roll. Many people will attempt to overcome this by increasing the spring rate of the rear springs to reduce suspension travel and use urethane bushings to control lateral movement. The result is an over sprung car that rides like a buckboard, and a rear suspension that binds.
Another shortcoming of 3-link, 4-link, and leaf spring suspension is that the car is being pushed around from the outer extremities of the chassis. Remember the wheels are not driving your car, its being driven by the suspension pickup points. What this does is creates a yaw intolerance that makes the vehicle more prone to spinout. The GM engineers address this problem by creating under steer in the A and F body lines on both the front and rear of the cars.
I could keep going, but I believe that the point has been made.
HRHP:
What is the History of Truckarm?
STEVE:
The main reason that GM put this rear suspension on their pickup trucks (hence the name Truckarm) was to satisfy a NASCAR requirement for factory rear suspensions. Equipping the trucks with Truckarm suspension made it legal for Jr. Johnson, and his crew chief, GM engineer, Ray Fox to use the setup on their 63 Impala for Daytona 1963.
As it appeared on the trucks it was awful. A half length panhard, above axle centerline, off on 2 planes, shocks at such an oblique angle as to be totally ineffective with the only real dampening coming from stiction in the rubber bushings on the ends of the shocks as the shocks themselves barely compressed. The arm angles and pickup points were also less then optimal. An afterthought, these trucks gave Truckarm a bad name. The trucks were over sprung, under damped, would not hook up, and had panhard induced bump steer that would actually make them do the hula.
The ill performance of the trucks aside, Truckarm use in NASCAR by Jr. Johnson got attention and it did not take long for the competition to follow suit. If it was not for engine failures Jr. Johnson would have been undefeated on the super speedways with Truckarm.
HRHP:
Why use it on my Hot Rod?
STEVE:
Truckarm is very stable and forgiving over high-speed bumpy surfaces. The long arms at a true instant center with the full-length panhard bar stay neutral throughout their range of motion. There is no bump or roll induced steering of the rear axle. The car is being propelled from the center of mass, which makes it very stable, and highly yaw tolerant. When the rear of the car steps out the propulsion points are at chassis centerline making the car very controllable. (The ultimate drifting setup) Also when you are on the throttle, torque reaction from the rear-end housing creates a lifting dynamic through the arms that tries to lift the car from the center of gravity. This lifting is what plants the rear tires so hard while at the same time keep the springs free to absorb surface irregularities. This is why forward bite is so incredible, but the ride quality remains so plush. A rear sway bar is not needed with a Truckarm system, as you are able to add roll rate with the throttle.
Testing before and after on acceleration runs have shown dramatic improvement in both trap speed and e.t.
With our screw jack system the car can be adjusted in seconds with a hand wrench.
They go like they are on a string, no wheel hop or twisting.
Under braking the rear brakes become much more effective, controlling the car from the center of mass. The torque reaction of the rear-end under breaking pulls the weight of the car down on the springs and in turn on the tires. The chassis also remains much flatter (less dive) and allows for some serious late braking. In test we have seen before and after improvements to braking by as much as 80ft with the same brakes.
What this is all getting at is that our American iron from the past can outperform anything coming off the assembly lines from Europe, Japan, or the US.
Nothing brings a smile to my face faster then watching some poor soul in his high priced import (sport car) spin out while trying to follow my 1966 Chevelle into a high speed corner on Angeles crest hwy.
HRHP:
I would like to thank Steve for taking the time to sit down with me and talk about his products and company. I hope that I will be able to spend some time talking with other vendors in the Hot Rod Industry and add them to the site.
