A purpose-built chassis built with stronger tubing or a full frame provides far greater torsional rigidity than the factorysupplied welded half-frame rails. The automotive aftermarket now has manufacturing equipment that only OEM companies used to possess. This technology allows these companies to research, develop, and manufacture complete chassis.
This Tech Tip is From the Full Book, CORVETTE C3 1968-1982: HOW TO BUILD AND MODIFY. For a comprehensive guide on this entire subject you can visit this link:
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Equipment for water-jet steel cutting, CNC machining, and mandrel tubing bending is available for companies to build new purpose-built chassis. They can build these chassis on CAD/ Cam machines and do it repeatedly. These are desirable chassis with the latest engine, transmission, and drivelines, allowing for late-model Corvette performance.
Do You Need One?
A full aftermarket chassis is desirable for high-performance applications and racing. This is certainly an option for a restorable C3 with a rusted bird cage, if you plan to complete a ground-up restoration with some aftermarket parts. An aftermarket frame and all the required trimmings is certainly a sizable investment, and with many C3s, it may not be worth the investment. Of course, that’s a personal decision. But keep in mind that an original chassis is a solid performance platform, and for most street-going Corvettes the factory chassis provides more than adequate performance.
You have to ask yourself if you possess the skill to drive a stock C3 beyond the limits of its chassis. If you do, you probably need a chassis with the latemodel components to match your skill level. On the other hand, if you do not possess the skill, do not expect the chassis to make you a better driver.
As far as cost, a bare purpose-built chassis is not that much more than buying a new original-equipment chassis. If you are careful about finding a donor car you could save considerable money. Then you can also offset the costs by selling some of the take-off parts from your original chassis.
Each chassis supplier developed and built a chassis that resolves the inherent shortcomings of the original chassis, and each has a different interpretation. You need to consider this aspect and determine what you want from the chassis. You may want a different wheel offset, but the builder does not offer that. In many cases, they do not make a major change in chassis width to accommodate your wishes. Think about the finished product so you can address all the details before you start on the project.
A few important suspension and steering upgrades occur with the aftermarket chassis. Rack-and-pinion steering is way up there and is much better engineered in an aftermarket chassis than the available bolt-on to the C3 chassis.
Suspension geometry with the increased positive caster is also important for high-speed handling. Depending on which generation of Corvette suspension you choose, you could also have true independent rear suspension with upper control arms for the best possible rear-end stability. The first designs were almost all for the C4 Corvette, which has a differential and rear suspension very similar to the Shark. Now many are available with C5 Corvette suspension for that ultimate handling and braking experience. C4 brakes can be upgraded, but the C5 brakes are better from the start so you can save a few bucks there too.
Three Project Examples
I have been a part of a few of the chassis builds and built a few from scratch and have found that compromises have to be made. My very first build was a 1961 with an SRIII chassis, then a Paul Newman 1968 chassis, and to date, a 1981 Corvette with a Street Shops chassis with C5 Corvette driveline.
When building a custom chassis, as I did for the 1961 SRIII, the level of planning and engineering is similar to building a car from scratch, although I had a completed bare chassis. I was one of the first few to buy a chassis from their first chassis design. As with any business, as the company evolves so does the product. Of course the 1961 chassis is different from the Shark, but the concept is the same, especially the work involved in engineering the entire package.
Many systems had to be customized and built, such as the fuel tank design and plumbing. Bumpers and safety equipment must be planned into the build. When building a project car, this is a critical job; it’s your responsibility and your life depends on it. Many want to personalize their project, not build an exact replica of their prototype. Designing a one-off car is no small feat, and it takes a lot of time, energy, and resources to complete a fabricated car with a custom chassis.
The Paul Newman chassis was even more difficult because they had not completed a Shark chassis yet. So, I started the project with a prototype chassis. Remember way back in the first chapters when I said that the 1968 was a 1967 in a Shark body? Well, this was the case here. The 1968 body was set on a Paul Newman chassis built for a 1967. Many things were not considered, which required hundreds of man-hours to come up with solutions to make the chassis work.
When I went to the shop to pick up the 1968 convertible project (that had been at two other shops), it was apparent that I had a monumental project to sort out. The freshly painted body was sitting on the aftermarket chassis with no bolts to hold it down. The pieces were gathered and off to the shop I went. During the initial inspection it was clear that no one had thought about how the C4 Corvette differential’s torque arm affects the 1968’s floor and transmission tunnel. With the torque arm installed, the entire side of the transmission tunnel and part of the passenger’s side floor had to be cut out to fit it in place. The customer wanted a full seat, not a jump seat, so I had to fabricate a differential mount that eliminated the torque arm.
Before I started that project I contacted the customer about wheel and tire choices to make sure the wheel and tire had that perfect spacing between the tire and wheel well lip. Good thing I did that, because the car sat like a 4×4 truck, requiring chassis modifications to lower it and raise the differential to get the driveline angles correct.
To make things even more interesting, when the Donovan aluminum bigblock with ZL-1 intake was set into place it sat 2 inches higher than it should, which prevented the raised hood from closing. I juggled things around, lowering the engine as much as possible with a Stef’s custom aluminum oil pan and raised the body 1 inch on the chassis to make it all fit. One other major problem was that no one had considered how the front bumper crash pieces or supports would be installed. They all required many hours of thought and hand fabrication to make sure there was crash protection and something holding the front end up.
The problems that arose from this project were not all the chassis supplier’s fault. Communication was the problem. These items should have been discussed long before the chassis assembly began. When the project had been successfully completed, it was one of my proudest moments. During the project, I went through many trials and tribulations. I asked myself, “Why did I inflict this much pain on myself?” Fast-forward to 2007: I have a Street Shops chassis to build for a 1981. This is one fine chassis made from rectangular mandrel-bent tubing with multiple suspension configurations available.
Street Shops has C4, C5, or C6 suspension mounting points chassis; I went for the C5 fully independent rear suspension chassis. This company has developed expertise from building many chassis. When they set out to make their chassis, wheel and tire width was a major player in how wide the track would be. To keep the Shark look, wheel width is limited to fitting under the original wheel wells using the same offset as the original Shark. This uniformity is the key to making them affordable and is what the builder had in mind from the very first chassis. In addition, Street Shops has fabricated brake and fuel lines for its chassis.
You can also buy a rolling chassis that allows you to lift the body off your original chassis and roll the new purpose-built chassis in place, ready to go with few delays. To make a project such as this affordable, you need to find a good deal on the donor car and then make the pieces come together for a personal touch. I found a running, driving 25,000-mile 2004 Corvette that had rollover damage. Many parts can be used, while others can be sold to make up for some of the cost.
One thing to consider is that you can build the entire chassis before ever touching your Shark if you are driving it presently. If you plan to sell the engine and transmission or, for that matter, the entire drivetrain, including the frame, potential buyers can test-drive the pieces before the disassembly, which makes them easier to sell. That can add up to a considerable chunk of change, offsetting the project cost dramatically.
Prep for Body Removal
You need to know that changing a chassis is a major event, and it involves a lot of tough work to get the body off the original chassis. The front, rear bumpers, and all the supporting structure must be removed. In addition, any cables, electrical, and parking brake hoses must be removed. The toughest of all requires the removal of the body mount cushions. In most cases, these have never been removed, or they have been in place for many years. Corrosion works on the body-mount bolt nuts. The idea was good when the cars were assembled, and as they age the nuts become one with the bolt.
Body Removal Prep
Step 1: Remove Rocker Panel
The rocker panels must come off to remove the front splash shields. This may seem simple enough: take out a few Phillipshead screws and the panel drops off. These screws can be difficult to remove since corrosion eats at them. It is difficult to get rust penetrant onto the threads: drilling the head off is sometimes the smartest plan. With the head off and the panel out of the way, rust penetrant can be applied and the remaining screw shank gripped with pliers for removal.
Step 2: Remove Bumpers
Chances are your Shark has rubber bumpers. I found that running a thread die on the bumper stud before attempting to remove the nut saves heartache down the road. These 10- to 24-thread studs are often broken from hasty removal, and it’s costly to replace as the stud comes secured in a reinforcement strip.
Step 3: Disassemble Bumpers
The front and rear bumper must be removed to lift the body. All of the bumper supports require removal. Here, the honeycomb crash absorber (to which the bumper supports bolt) has been removed. This is a major undertaking and much more than a chassis replacement is going to occur. Many issues with the body may be found, such as rust and corrosion damage to the steel fiberglass support structures.
Step 4: Remove all Grounds
Sharks, like all Corvettes, have numerous grounds at the front and rear of the chassis. Removing them is one thing; making sure they are all put back on is another. One missing ground wire can keep you busy for days chasing a phantom electrical problem. Make sure you note where the grounds are and put them back with adequate wire and fasteners after a thorough cleaning of the terminal and mounting area.
Step 5: Remove Cables and Wiring
Throttle cables and tachometer (pre-1974 Sharks) cables must be removed before the body lift. The engine harness requires removal before the lift, and the alternator power output lead must be removed. Take your time here; leaving a cable or wiring connected usually does more damage than just to the connected piece. I have seen serious component damage as the wiring is being pulled.
Step 6: Remove Steering Column
You can either pull the steering column or remove the steering coupler nuts as seen here. As the body is lifted, the coupling separates. I usually remove the steering column completely to make this as easy as possible. During the body installation it is best to have the steering column out of the way; aligning the coupling during the body drop is difficult.
Step 7: Remove Parking Brake Cable
If this step is missed it could be disastrous; the parking brake cable goes around this pulley wheel, which must be removed. The parking brake cable must also be disconnected at the rear cable that goes to each trailing arm. I cut the old exhaust pipes off at the crossmember to remove the entire rear section of the exhaust. The mufflers get in the way of the rear fenders during body removal.
Step 8: Remove Radiator Core Support
The Shark radiator core support sits on top of the bumper support. I usually leave the radiator core support bolted to the inner fenders and remove the two 5/8-inch hex-head bolts holding the radiator support to the frame. Sharks from 1968–1972 have the radiator core support held in differently than this 1979, but the concept is the same. Make sure you remove the proper bolts. Loosening these bolts helps when it comes time to remove the radiator so that the core support tilts forward with less effort.
Water with all kinds of road minerals is thrown onto the body cushion bolts, requiring careful work to avoid major body damage. Using a torch around fiberglass is not recommended. Many people do and the burnt fiberglass shows. Rust penetrant works, but you need to think it out and begin dousing the bolts and nuts for weeks before you remove the body cushions. Sometimes you get lucky and the bolts break off, but most often they just spin and you must cut the head off the bolt. The body cushion bolts behind the rear wheels are always the worst. Fortunately, they can be cut off with a reciprocating saw.
Body Cushion Removal
Once the body is up and off the chassis, you need to inspect the C-channels that run under the sill plates. The C-channels are a crucial part of the birdcage structure supporting the Shark-body passenger compartment. If you find any rotted areas, they need to be properly repaired even though they are not visible. If required, you weld patch panels into the C-channels, especially around the body mount cushions. The areas around the body cushions often have the worst corrosion damage. Then you need to apply some primer and paint.
You should also make note of the body cushion shims. You have to put them back where they came from so the doors open and close properly. I often find that it takes some additional or sometimes fewer shims to get the door gaps uniform after a major project like this. This is a trial-and-error procedure unless you have shimmed a body a few times.
For instance, if the rear door gap is open too much at the top you need to add shims to number-4 body mount in the wheel well behind the rear tire. Always check the body gaps and shim with the tires on the ground, with no jack supporting any portion of the vehicle.
Body Cushion Removal
Srep 1: Body Cushion Removal
This is a common sight: a very rusty bolt sticking through the number-4 body mount retaining nut. The rear speakers are removed from this 1979 to gain access to this caged nut. Convertible Sharks have these nuts behind the rear deck supports, making them very difficult to access. A thin steel cage riveted to the fiberglass floorpan was used to prevent the nut from spinning, which breaks immediately because of corrosion. I soaked these nuts for days before trying to remove them. A crescent wrench can sometimes be used to hold on to the nut while someone turns the bolt from the bottom. Using an impact wrench helps immensely to hammer at the nut during removal as opposed to trying with all of your strength to pull on a ratchet and socket setup. Using to use the impact on a low setting, letting it slug on the bolt and knocking the rust loose.
This is often the alternative to removing a rusty bolt that does not cooperate; a reciprocating saw does a decent job of cutting the bolt. The problem is that the bolt begins to spin from all the force the saw places on it and then the bolt must be held from inside while the saw cuts the bolt. The bolts are also pretty tough, so the cut takes a while.
Step 2: Remove Number-1 Body Bolt
This is by far the easiest body bolt and nut to remove: the nut and bolt are both accessible after the lower splash shields are removed. If you’re lucky the bolt may break; if not, plenty of rust penetrant helps. I have found that loosening the bolt some and reapplying penetrant helps, then reverse the impact and tighten the bolt and apply more penetrant. The back-and-forth action along with the penetrant helps the removal process immensely.This special tool was made from a piece of bar stock. I found that by forcing it into the space between the body mount nut and frame pocket, it usually stops the nut from spinning. The tool is hammered tightly into the space. I have used this tool countless times with excellent results. Size does matter; take a little off at a time, making it end up with a square section about 2 inches long at the end to be inserted.
Step 3: Remove Number-2 Body Bolt
The use of an impact wrench can save many hours of aggravation removing the number-1 and -2 body mount bolts. The hammering effect of the impact wrench helps break the rust and corrosion from the threads, saving valuable time and possibly more work. Number-2 body mount bolts are behind both kick-panels. This 1979 Shark had clean, almost rust-free number-2 body mounts. Many of thesebody mount bolts are rotted away.
Lifting the Body
Our project required more work because it used the C5 Corvette differential assembly. The entire back section of the floor had to be removed to fit the body. Once the body was mounted to the chassis, a modified rear floor section was constructed to make the plan work.
This project used a late-model drivetrain, and that produced excellent fuel mileage. In addition, there were many other benefits to the project. Even a factory original engine exceeds 300 hp, and then there are the bigger brakes. These components on a purpose-built chassis are important on a road course or at autocross events.
Lifting the Body
Step 1: Use Cherry Picker or Two-Post Lift
I used a tow strap to lift this 1981 Shark body off the original chassis. The door bars were made from fence posts, then bolted into the door hinges and striker; they made excellent lift points for the strap. I used another strap from the front to the cherry picker to stabilize the body during the lift. The front strap is also holding on to the radiator core support, which is the only place with enough strength to avoid body damage.If at all possible, use a two-post lift. You can slowly raise the body without it swaying, or hoping that you have the body weight balanced. Keep a watchful eye as the body passes by the number-4 body mount behind the rear tire. The body comes very close at this area on all Sharks;
using the cherry picker can cause some body damage if you are not extra careful during the lift.
Step 2: Prep for Body Drop
The Camaro Tremec T-56 6-speed transmission requires a new opening in the floor for the new shifter placement. I cut the smallest opening possible for the initial body drop, hoping to avoid adding material once the body is fitted. Depending on your drivetrain and particular year Shark, this opening requires modification to make the shifter work.
Step 3: Remove Floor Section
Our ambitious project was to use C5 1997–2004 Corvette suspension/driveline components on the Street Shop chassis. Because of this, we had to remove a major section of the rear compartment floor to fit the chassis. I do not recommend this for the novice or first-time builder; serious fabricating skills are required to build any floor section from scratch. The preliminary cut was done with a small, handheld air-powered reciprocating saw, leaving enough material to do a final cut.
Step 4: Build New Floor Section
As you can see, the entire rear floor section is removed for the trial fitting of the body on the chassis. I do not spend a lot of time cleaning or prepping anything until the pieces are close to their final form. My policy when doing any project like this is to make everything work, then take it apart and make it pretty if you are inclined to do so. You can expect to have the body on and off numerous times until all of the areas are worked out. That is why I say this is for experienced builders. Street Shop does have a C4 suspension and driveline package for their chassis that does not require this much surgery. You should consider this for your first major build if a purpose-built chassis is for you.
Step 5: Build Floorpan
I use 22-gauge aluminum panels to make a “buck” fiberglass mold for the modified floorpan. Three separate pieces are formed using hand tools for the preliminary buck. Each panel is fitted carefully with one thought in mind: always remember that the thickness of the fiberglass has to be added to computations. This is where careful fitting is important for the least aggravation.
Step 6: Make Fiberglass Panel
The inner surface of the aluminum buck is covered with PVA, a release agent for the fiberglass panel to come off the buck. You may want to put your fiberglass on the outside of your buck; it all depends on which side you want to be smooth. The smooth side is always against the PVA. PVA can be found at most paint and body suppliers or marinas. The side pieces are glassed first, then the center is added for a final fiberglass mat application to make it one piece. Although you may not do a major C5 suspension/ driveline purpose-built chassis, most performance vehicles get some fiberglass modifications. The same techniques can be used for any fiberglass addition.
Step 7: Install Engine
The 1968 Shark Paul Newman chassis required a unique fix to our large-cubic-inch big-block engine installation. The injected big-block required a special hood to fit over all the components; the raised hood was not going to work. The solution was to raise the body 11 ⁄4 inches with the aluminum spacers shown. The engine was set as low as we dared allow it for the already lowered chassis. The lower you can get the center of gravity, the better. The conundrum was that the 18- and 19-inch wheels required the suspension to be raised anyway; this fix solved both issues. The wheel/tire combination fit in the wheel wells and the hood was not an issue. No one was aware of the solution. This is what it takes sometimes to make all of the things you want to come together.
Suspension and Drivetrain Installation
Step 1: Suspension and Drivetrain Installation
C5 Corvette suspension components are installed on this Street Shop chassis. The assembly is simple due to the use of factory components. The mandrel-bent frame rails make it a very strong chassis with minimal flex. Coil-over shocks are used on all four corners for the best handling and adjustability. Corvette 2004 OEM upper and lower control arms are being installed onto the frame from our donor car. The plan is to assemble the entire project, making sure the driveline and suspension perform to expectation. After that, the entire project will be disassembled. Then, the pieces will be cleaned properly and refinished.
Step 2: Install Brakes
All of the 2004 C5 front suspension components have been transferred to the new chassis except the power steering rack. After the upper and lower control arms were installed, the complete spindle assembly (with brakes) was installed on the upper and lower ball joints. Street Shop provides a modified rack-and-pinion steering to accommodate the Shark’s track, which is narrower than the C5. This steering rack, complete with outer tie-rod ends and urethane mounting bushings, bolts in place with the hardware provided. Street Shop includes a power or non-power steering rack in the chassis package. They also provide a modified front anti-roll bar and links for simple installation. This well-thought-out chassis has the frame rails in the same place as the factory rails, so the original bumper supports work without a hitch.
Step 3: Install Control Arms
This is where the C5 shines: it has upper control arms to positively position the rear spindle assemblies. The lower control arms are part of the rear crossmember and cradle assembly. Street Shop modifies the factory cradle to fit the C5 suspension components into the original Shark’s narrower tire track width. For the first time, constant-velocity axleshafts were used on a Corvette C5 chassis to handle the suspension geometry changes as the wheel travels throughout its up-and-down range. The upper control arms are being installed onto the frame after the supplied U-brackets were installed on the control arms. At this point there is no need to tighten everything fully. Snug is fine; wait until all the pieces are together for the final torquing. You can use a factory C5 service manual for the torque specifications, including the U-brackets for the upper control arms; General Motors provides torque specs for the appropriate bolt diameters. Having a bolt and nut thread gauge handy during chassis assembly is always a good idea with metric fasteners. It gives you millimeter thread and bolt diameters quickly.
Step 4: Install Rear Suspension
Once the rear suspension is assembled, you can see that even at the highest point of suspension travel the rear wheel camber is close to zero. This is why the C5 Corvette handles better than its predecessors, maintaining the wheel alignment throughout the suspension travel. All factory torque specifications are used for the suspension assembly. I had a dilemma since I chose the C5 suspension and driveline system with rear-mounted transmission that uses a torque tube to connect the engine to the transmission. The C5 differential has no yoke to connect the torque tube to the differential. 21st Century Street Machines provided a rare conversion kit (no longer in production) that uses a Ford 9-inch conversion plate to front bearing assembly. Street Shop has a couple of other options to make the C5 rear suspension work with a Dana differential. One is a Viper style and the other is their proprietary assembly design. Regardless of the differential you choose, Street Shop has the mounting brackets and supports ready to go for a simple bolt-in.
Step 5: Install Engine
The crate LS6 bolts directly into the chassis with an LS Camaro T-56 6-speed transmission for propulsion. All of the driveline angles have been determined by Street Shop and set appropriately, making this a simple drop-in of components. Unlike the LS transplant in Chapter 2, this chassis allows the use of a complete C5 Corvette engine without an oil pan change. The C5 engine mounts can be left on the engine and simply bolted into the chassis. Modifications are the same as with the LS engine transplant, including the cooling system, heater hose, and accessory installation. For that matter, due to the Shark body and chassis constraints, there is no difference to the engine install whether it is in this purpose-built frame or the factory frame. The major differences are the suspension and rear driveline component configuration.
Step 6: Install SRIII Chassis LS Ancillary Components
SRIII Motorsports made enough room in the chassis for the C5 Corvette accessory drive system, placing the A/C compressor low and out of sight on the passenger’s side. While this is a clean setup, placing the A/C compressor down low can be troublesome to service in the future because of tight fitment of the compressor and limited access. However, a complete take-out used C5 Corvette engine assembly can be used with all factory pieces. This is something to consider if you are a long-hauler; parts availability is much simpler if you are looking for factory parts over custom pieces. The heater hose connections are also tight because of the inner fender once the body is in place. Street Shop chassis require the use of aftermarket accessory drive supports to fit their frame. Although such small things may seem insignificant, the cost adds up. Fabrication skills are high on the list for hoses, supports, and all sorts of required ancillary components.
Step 7: Install Wiring Harness
A set of 2001 Camaro LS exhaust manifolds were used for the engine installation because they fit close to the engine, clearing the frame rails. This GM LS crate-engine harness was routed onto the engine before the body installation to check fitment while it was easy to access the engine. You need to integrate the engine harness with the Shark’s original harness. This comes down to preference: you are embarking on a custom path that requires you to work with all of the Shark’s existing and add-on wiring systems. Very few of these projects are similar in the builder’s choice of accessories or aftermarket components, including the engine’s control system. The best possible solution for the novice is to use an engineered wiring system from a company such as Painless Performance, which has intimate knowledge of the LS engine requirements and the Shark body you are using.
Step 8: Install Coil-Over
SRIII Motorsports incorporates coil-over shocks in all of their chassis builds (see Chapter 10). Depending on the chassis you choose, coil-over shock installation is quite easy: place a bolt, washer, and nut in the mounting points. Make sure you torque the bolts to the chassis supplier’s specs, or use the thread fastener gauge to determine the bolt size for the proper torque spec. SRIII supplies the rear toe link that bolts to a modified differential cover. You have to modify your cover per their instructions and then clean up the cut-off areas with a coarse grinding disc. C4 Corvette factory-style camber rods are used at the bottom of the differential; this aftermarket performance set with urethane bushings is from Vette Brakes and Products for simple rear camber adjustment with minimal deflection. They can recommend the correct spring rates for the best overall handling. Keep in mind that they have built plenty of these assemblies and have driven them to prove what works. This C4 suspended chassis uses all the original components, which is important if you plan on really driving your project. Nothing is worse than having a part failure and hearing that you can’t get them for two weeks or more on a road trip.
Step 9: Inspect Assembled Chassis
The Street Shop chassis is a “roller,” ready for body installation. I tried a set of C5 Corvette headers hoping that they might fit; unfortunately, they come too close to the transmission. Street Shop has prebent fuel and brake lines to make a very tough part of the project much easier. I prefer to make my own because I have all the required tools; this can be pricey for one-time use. The chassis can be put in the corner until your Shark is ready for the transformation.
Written by Chris Petris and Posted with Permission of CarTechBooks