Classic Corvettes get vibration and noise isolation from a succession of soft, flexible rubber and steel components designed to soak up road boom and powertrain harmonics to make the going quieter and smoother. Back in the day, new Corvettes were fitted with rubber parts throughout the suspension, exhaust system, engine and driveline. All of it was designed to deliver a comfortable driving experience.
Today, we want a more hardy driving experience where a classic Corvette exhibits better road manners than it did decades ago. Suspension technology has brought us better vibration and noise isolation in the form of Hyper-Flex polyurethane from Energy Suspension, which outperforms rubber by a wide margin.
Energy Suspension tells us factory suspension bushings and mounts are generally made of steel and rubber for good noise and driveline isolation. Rubber is very flexible, which means you’re going to experience a lot more flex in places where you’re not going to want it, such as the suspension, which is unacceptable when you’re headed for the road course. When rubber suspension components flex it changes the geometry, which tends to throw handling off in the twisties.
The black rubber originally installed on classic Corvettes was made from petroleum byproducts as opposed to natural rubber. Polyurethane is a “reaction polymer” created in a thermoset process, which is more common today than rubber. What’s more, polyurethane is virtually indestructible and outlasts rubber. “Rubber” is used to describe factory bushing material and “polyurethane” is used to describe Hyper-Flex, the proprietary material used by Energy Suspension in its polyurethane products.
Why is it important to have reduced flex from our suspension systems? Because the flexing of suspension components slows a chassis’ response to input creating an obvious disconnect between driver, chassis and the road. In tire and suspension testing and research, engineers do a “step and steer” test, which involves driving at a constant rate of speed, quickly dialing in a specific steering attitude, holding that input, and then measuring the car’s response to input. Most vehicles will have an initial reaction and then a secondary reaction after everything settles down. While some of this “settling” is tire reaction, a lot it comes from suspension deflection and sloppy geometry where a test vehicle plows all over the place.
Polyurethane design and manufacturing isn’t as simple as it may seem. Hardness is measured on the Durometer scale. There are two main scales followed by either A, D or OO. Tires, as one example, will have a Durometer number of 60A while a solid hand truck hard rubber wheel is a 50D. These two systems operate on the same testing procedure of probe pressure into the polyurethane or rubber to determine hardness.
Energy Suspension focuses primarily on the Durometer scale to measure hardness. If you think about it on a small scale, a polyurethane or rubber bushing is a suspension system for the suspension system. How does the material compress, deflect and spring back? If you get tremendous pressure and no damping, you get a vehicle that never settles when it gets rough and you wind up all over the road. The harder the material the less damping occurs.
Polyurethane bushings last far longer than rubber because they’re resistant to heat, ozone and harsh chemicals. If you keep polyurethane parts lubricated, and you will rarely have to do this, they can last the life of your vehicle.
What kind of performance can you expect from Energy Suspension parts, which we obtained through Summit Racing Equipment? Road racers will experience better lap times thanks to the firmness of Hyper-Flex, which minimizes unwanted geometry changes. If you’re more inclined to go drag racing, expect to see better elapsed times beginning at the 60-foot mark because you’re going to hook up better and at the top end because your front wheels are staying straight and not deflecting outward, which slows you down. Vette
1. Energy Suspension Hyper-Flex control arm bushings take all of the twist and shout out of a classic C2, C3 or C4 suspension system. The advantage to using polyurethane bushings is reduced flex and increased durability.
2. When you install fully adjustable Energy Suspension engine mounts, you will notice an immediate difference in the way the drive feels because these guys isolate engine harmonics better than the OEM engine and transmission rubber mounts. They provide a firmness you will never feel with rubber mounts.
3. Choosing the right Hyper-Flex polyurethane product from Energy Suspension is a matter of understanding hardness, which is tested with a Durometer. The harder Hyper-Flex bushings will firm up your handling. By the same token, engine, transmission and body mounts need to have more give to better isolate road boom and powertrain NVH (noise, vibration, harshness).
4. We’re working with a ’67 427 Corvette at California Muscle Cars. We’re going to replace nearly every bushing in this C2 Vette. We’ll begin at the front suspension by removing the shock absorbers.
5. When you disassemble the frontend, take a picture of the upper control arm alignment shims. Tape the shims together and mark where they came from so you can reinstall them in the same spot. However, you should still get a frontend alignment after the bushing change is done.
6. Kirk Peeler of California Muscle Cars slowly takes the screw jack pressure off the lower control arm and releases the spring.
7. The lower control arm is removed next using a 7/8-inch socket.
8. We’ve placed the upper and lower control arms on the workbench for inspection and replacement of the bushings and ball joints. Summit Racing Equipment has provided us with Moog ball joints and tie-rod ends to make this job complete.
9. Penetrating lubricant is applied to the control arm bushings and hardware to make removal easier. Closely examine the shaft after you remove the bushings. If there’s excessive wear and pitting, replace the shaft.
10. Energy Suspension sleeves have been pressed in first in a vice or hydraulic press then, followed with black Hyper-Flex bushings and sleeves. Lubricant is provided with the bushings to make the going easier. Wear protective gloves with this lubricant. Driving the old bushings out requires an air chisel and a certain amount of patience.
11. This is what the Energy Suspension bushings look like installed. They provide unending support and will last the life of your Corvette.
12. Since we have the control arms out we’re also installing Moog ball joints from Summit Racing Equipment for durability. The old ball joints suffered from split boots and excessive wear.
13. The lower control arms, which have been completely rebuilt with new Moog ball joints and Energy Suspension Hyper-Flex bushings, are installed at this time.
14. The upper control arms, also fitted with new ball joints and bushings, are reinstalled through the top as shown, with their shims correctly positioned.
15. The front coil springs and brakes have been reinstalled and we’re ready for the stabilizer bushings and endlinks. Because there are various sized stabilizer bars you may have to bore the bushing out or specify to Energy Suspension the stabilizer bar you have. Because Hyper-Flex stabilizer bar bushings are decidedly stiff for handling purposes, you may have to lean against the bar to get bolt thread penetration.
16. We’ve opted for Moog tie-rod ends from Summit Racing Equipment. The original tie-rod ends have been measured and we’re setting the new ones up per the same measurements. You may also count the number of threads visible and use that as a reference.
17. Energy Suspension body mounts provide excellent support. Choosing them depends on the type of drive you’d like to have. Rubber body mounts isolate the road in an OEM type of way. Hyper-Flex mounts provide a more solid driving experience.
18. Body mount replacement can be darned tricky. You must carefully lift a Corvette body off the chassis. If you are not careful, you can crack the fiberglass.
19. We have installed the lateral spring mount Hyper-Flex bushings, which install with ease. Where it gets challenging are the shims, which go on top.
20. Shims at the lateral spring mounts install like this and they can be a bear to get in there. The suspension has to be manipulated in such a way that you can get them in.
21. The rear stabilizer bar has endlinks sporting rubber bushings like this. Hyper-Flex endlinks will make a huge difference on how this big-block Vette will handle.
22. The old rubber stabilizer bushings have been pressed out. Getting the new Hyper-Flex bushings in is a challenge because they are so stiff. Bushing assembly lube will make it easier to press the new bushings in.
23. Solid, increasing pressure on the bushing in a vice or hydraulic press will get the Hyper-Flex bushing in place. Next is the steel sleeve, which is pressed into the bushing.
24. Once the bushings are pressed into each end of the stabilizer bar we’re ready for installation. A footnote to this procedure is the need to remove the spare tire and cover to get the stabilizer bar out.
25. The stabilizer body mount and new bushings are installed next, which completes the stabilizer bar installation.
26. Particularly challenging to replace are the rear strut rod bushings. When you remove the strut rods you disturb the alignment, which will call for a four-wheel alignment. This is an eccentric, which adjusts the strut rod in or out.
27. This is one of the Hyper-Flex strut rod bushings, which must be pressed into the strut rod. Because this Corvette’s owner didn’t want to disturb the alignment, we’re showing you where it goes.
28. Before you is the C2/C3 independent rear suspension with its fixed differential and transverse multileaf spring. These suspensions aren’t always for the novice. It is best to consult with a chassis professional if you’ve never had an experience with these before.
Photography by the Author and Energy Suspension