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In our last issue, we started our look at triangulated four links for GM G Bodies (and much of this is the very same for earlier A-bodies too). We pointed out there were and still are a number of different rear suspension options for drag racing these cars, but the very best scenario is where the bars are adjustable, the shocks are double adjustable and a high quality Anti Roll Bar is used at the rear.
The stock G Body I/C location isn’t really that bad. Believe it or not, many of today’s very successful Pro Stock drag cars have instant center locations way ahead of the vehicle. In fact, many torque arm suspension combinations (for example, a 1982 to 2002 Camaro) that are known to hook pretty much on grass have a long I/C location. Crank in big power with your G-body and you’ll likely find that an I/C location near stock is actually close to optimum, provided you don’t jack the body way up in the air.
If you have some adjustment in the bars (for example, adjustable uppers and lowers), then you can fine tune the suspension and set the static pinion angle. What’s with big deal with pinion angle? It is a very big deal. In order to keep the driveshaft and u-joints operating in a (more or less) straight line, the pinion angle has to be correct. Typically, the pinion angle is measured between the pinion gear flange and the driveshaft. As the suspension in a car “wraps up”, then the pinion is driven upward (out of whack). To ensure that the pinion is in the correct location under power, it is typically set nose down static. For cars with spherical bearings (rod ends) or solid back suspension bushings, most people strive for a pinion angle of between -1 to -2 degrees (- is negative angle, or pointing “down”). If the car has OEM style rubber suspension bushings, a pinion angle of -3 to -4 degrees is likely more appropriate.
Preload is another major tuning tool, but in a triangulated four link, there is a big (as Big) caveat: In a high horsepower car, the engine torque tends to roll rotate the chassis. This means the car has more bite in the right rear. In turn, that bite tends to move the car toward the left. In a lower powered car, the forces that rotate the rear end (torque rotation) tend to provide more bite to the left rear tire. In either of these cases, you can counteract these forces with preload. In a conventional, non-triangulated four link (like a dedicated drag race car setup), you can shorten the upper right bar to increase the preload on the right rear tire. If you can lengthen the same bar, then more load is placed on the left rear tire. Sounds good, but here’s the rub:
On cars that have the triangulated upper control arms (GM A and G Bodies) setting preload isn’t possible with the upper bars. When you adjust only one upper control arm then you actually shift the rear end housing left or right, depending upon which bar you try to adjust. The upper bars on a triangulated 4-link are used to center the rear end housing from side to side (by adjusting one upper). The upper bars also used to set the pinion angle (by adjusting both uppers the same direction and same amount). Adjustable lower bars are used to center the tires front to back in the wheel well and to make minute wheel base dimensional changes. To preload the suspension in a G Body (or A Body), a sway bar (anti-roll bar or “ARB”) is most often used. From here, you use adjustable shock absorbers (front and rear), front suspension limiters and to a lesser degree, specific spring rates to get the car to hook, but as you can see, the trailing arms are major traction players. For more on ARB’s, follow this link:
https://www.racingjunk.com/news/loose-as-a-goose-why-arbs-are-necessary-in-most-drag-cars-part-iv/
Finally, check out the accompanying photos. They’ll give you a good idea regarding what’s hot for high quality, bolt-in rear suspension hardware for your Malibu, Grand National, Cutlass, Monte Carlo or El Camino.
Autofab Race Cars
7443 Washington Blvd.
Elkridge, MD 2107
PH: 410-796-8777
TRZ Motorsports
1651 Kelley Ave
Kissimmee, FL 34744
PH: 407-933-7385
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Here’s a look under that Buick shown in the opening photo. It’s equipped with stock stamped upper trailing arms. Meanwhile, the lowers are lift style bars with revised geometry. In this case, the geometry wasn’t working. It was trying to rip the rear end out of the car (with an extremely short instant center).
This is an overview of high quality adjustable trailing arms from both Autofab (grey hammerstone) and TRZ Motorsports (black). TRZ’s spherical bearing housing bushings are on the right and just above them are Autofab’s chassis braces.
Here’s a better look at the pair of adjustable upper trailing arms. The black arms (top) are from the folks at TRZ Motorsports. The grey arms (bottom) are manufactured by Autofab Race Cars.
Overall configuration for both sets of uppers is similar. They offer considerable adjustment capability. More in the next photos:
These are the adjusters found on both bars. The idea here is to allow you to change the upper bar length (see the text for more info) without removing the bar from the car.
What’s the difference in rod ends? The big difference is the size of the aluminum spacer. It really doesn’t have an effect upon performance.
Out back, each bar is setup similarly (there are detail differences, such as the clearance notches Autofab incorporates).
Essentially, these pieces wrap around the upper bushing on the rear end housing. More on bushings later.
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GM G Bodies are popular drag race platforms. No question about it. When it comes to availability, the cars are still out there and while prices have escalated for nice examples, they haven’t gotten completely out of control. With that, there’s also plenty of info out there on how to make a coil spring car like a late model Malibu, a Cutlass or a Grand National work down the straight and narrow. Some of the things you’ll run across include airbags (either one or two), so called “lift” bars, “no hop” bars, ladder bars along with a whole bunch of questionable bolt-on paraphenalia. Some of that either works a wee bit or doesn’t work at all. Some is worse. I’ve had the opportunity to live with a set of name brand lift bars (complete with revised pickup points) on a Turbo Buick. They might have worked, but the geometry was so bad you could see where the bolt holes for the bars (drilled into the rear end housing brackets) were becoming oval. Simply stated, those bars were trying to rip the rear end right out of the car. Nice.
So what’s the real solution for a G Body? Big power will usually lead to tire smoke. How do you make it work? As far as the back end of these cars is concerned, there are three major ingredients to “hook”: Shocks, anti-roll bar, adjustable trailing arms. If you have an early GM A-Body (for example, a vintage GTO, SS396 Chevelle, 4-4-2 and so on), you’ll find they pretty much use the same hardware layout, although the respective bits and pieces don’t interchange between generations (A Body to G Body and vise-versa).
The real meat and potatoes of the back suspension happens to be the upper and lower trailing arms. GM used u-shaped stampings for the trailing arms. They’re not the most robust pieces available. You can get boxed style replacements, but the real key is to install tubular pieces with adjustment capability. What’s so important about adjustment? One big isue is to establish a working pinion angle, but that’s just the beginning. The real key is to first understand that the coil suspension found on GM G body is nothing more than a four link with angled trailing arms. By laying out the suspension with angled bars, it meant GM didn’t have to worry about a means to control lateral movement in the rear end. Instead of using some form of track locator or Watts linkage, the trailing arm triangluation keeps the rear end in the car. With this arrangement the bean counters were happy (no added parts means less cost), but so were the engineers (no added parts means less unsprung weight, which equates to better performance).
So far so good. The big issue here might be the fact the instant center (I/C) location on these cars is way out there (to the front – in some cases somewhere close to the engine). And in many cases, the I/C is rather high (due to the angles of the bars it can be somewhere above the front wheel spindle). Whoa. What’s “instant center”? The instant center or “I/C” is an imaginary point about which the chassis or a suspension member rotates in a given (instant) position. It’s found by projecting lines along suspension members to a point of intersection. This intersect point is called the Instant Center. The I/C acts as a pickup point for the back suspension, even though the points are imaginary.
The problem with many of the no hop or lift style bars or any of the other traction devices for A and G-bodes is they tend to create a very short instant center (by changing the angle of the bars). That might work for a low powered car but as you feed more power to it, it just makes the car [very] violent. Worse, some of the top mount bars (that raise the upper trailing arm location on the rear end housing) have a tendency to hammer the trunk floor when you get on the throttle. Not good.
That’s a wrap for this issue. Next time around, we’ll dig deeper into the basics of G-Body traction. Meanwhile, check out the accompanying slideshow with photos of high quality, adjustable trailing arms from both Autofab and TRZ Motorsports.
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