Thursday, February 10, 2011

C3 Corvette Driver Frame Off Restoration Part 3

The article featured on this page is from the March 2011 issue of Auto Enthusiast Magazine.



Fun in Any Year (Part 3)

A hands-on approach to bringing back a C3 chassis.

Story Chris Petris

Images Stephanie Petris

Like any good wedding, preparation and planning makes our trepidation-filled day easier. Our planning started with installing our A/C, interior and exterior components.

Wiring for our radiator cooling fans, MSD ignition, etc. also made good sense with the engine and chassis out of the way. New aftermarket two-gauge battery cables will be installed after the body drop. Originally, we planned on installing the cables before the body was in place. Our concern was crimping the supplied terminals to the cables once they were installed.

Extenuating circumstances required us to fit the cables for length with the body installed. We would have to fit the battery cables then remove them for crimping. This is why it is important to plan the assembly as extra work is created from lack of or poor planning. Stepping back and thinking out the best plan of attack will ease the aggravation factor and possibly save dollars in the long run. Replacing the positive battery cable is no easy task on a completely assembled 1968-1982 Corvette. This information reminded us that we should attack the battery cable assembly and installation right after the body drop.

The Body Drop

We were ready to lower the body down onto the new rubber body mounts. Why use rubber body mounts not urethane? We wanted to avoid an even harsher ride from the already installed urethane suspension bushings. GM used four rubber body to chassis mounts with shims on each side to correct for any build differences. We usually try to record how many shims came out of each position and put the like amount in place.

This theory does not always work when corrosion has eaten up the shims or they are corroded into one big lump. Our situation was the original body mount bolts were loose (never tightened at all) from the original factory build. In fact, there was a rubber mount and bolt never installed, allowing the shims to fall out from the factory build. We would have to install shims as close to what we could determine was correct as a starting point. After the body is dropped we can add or remove the necessary shims.

The idea is to avoid body and front-end fiberglass stress while maintaining proper door gaps. We also need to look at the front fender to door gap when positioning the front bumper support. The front bumper support/crash bar is used to hold up the front fenders at the radiator core support area.

Once the body shims are installed, both doors should be checked for correct operation. When the doors are closed or opened, they should not drag or bind. This is where you should be looking at notes from the pre-disassembly phase of the project. If the doors worked fine before disassembly, they should now. We do not want to try and correct a poorly fitting door with shims if it fits poorly from worn hinges.

In our case, we had a good door fit on the passenger side with good tight door hinges. So we shimmed the body on the passenger side until the door opened and closed properly with good body fit lines. The driver door was another situation altogether; the door hinges were loose and the door was sagging from our pre-inspection.

Stocking up Shims

If you are working on a lift, drop the chassis down on the tires and roll it back and forth to settle the chassis. Do not try to use the body mount bolts to close a gap between the mount and chassis. Shims must be used to fill the gap or fiberglass structure damage can occur. Use the two line-up holes in the body sill plate area and chassis to align the body on the chassis. Use never-seize on the body mount bolts — who knows, you may be the one taking them out again one day.

We found that there was clearance for shims between the body mount and the two front chassis mounts. This was with the body sitting on the mount in front of the rear kick-up. We should use the mount in front of the rear kick-up as the starting point. Does the rear-most mount behind the rear wheel have shim clearance also? Any way you look at this situation, if the original body mount shims are not available for reference, you need to juggle things around until the correct combination is found. After the body mount shims are corrected, the mount bolts are installed and tightened.

Our final body mounting adjustment concerns the front end fiberglass. From the front of the doors forward, there is no rubber mounting used. The radiator core support has the inner fenders fastened to it. Front bumper supports have provisions for the radiator core support to sit on and be shimmed accordingly.

Over time, the front bumper support can drop, stressing the front end fiberglass. This is a really bad thing, as pressure is applied to the front fender bonding areas at the firewall. GM used a triangular-shaped fiberglass mount by adhesively bonding and riveting it to the upper firewall. The resulting stress from the mispositioned front bumper support loosens the triangular-shaped mount. The mount rivets loosen, allowing water to leak into the cockpit. It is common to see a wide gap at the upper front fender to door as the front bumper support slowly drops. It is always a good idea to keep an eye on how much gap there is between the upper front fender and door.

Chassis Set-up

Once the body and chassis are shimmed properly, the tough part is over. We install the crash bumper hardware, then the urethane bumper covers. Once the major components are installed, we check the basic front and rear alignment. We want the vehicle weight to be close to maximum when adjusting any alignment components.

At the front end we are concerned with toe-in by measuring between the center of the tires front and rear. Somewhere around zero to an 1/8th of an inch toe is good. That means that the distance between the center of the tires is exactly the same, or the front of the tire is no more than 1/8-inch closer than at the rear of the tire.

At the rear suspension, we usually install the shims that adjust the toe-in with equal amounts on either side of the trailing arm bushings. The rear camber adjusting cams are adjusted to keep the wheels straight up and down. These adjustments will get you to the alignment shop without eating up your tires.

Finishing the Fitment

There are a lot of electrical connections to make next. The majority of connectors are proprietary to avoid incorrect connections. Be sure to connect the ground cable from the engine to the frame or risk damage to many metal cables or wiring. We have seen automatic transmission selector cables melted because they were used for engine grounding during starting. The ground load has to go somewhere if the ground cable is not connected.

Now on to the final underside pieces to install, like adjusting and aligning the exhaust system. Our shorty headers were installed before the body drop while we could easily access the engine. Now we can install our exhaust with the body in place to avoid floorboard to body interference.

Installing the steering column coupler and checking all the suspension/steering components for tightness should be next on the list. Brake hard lines can be connected and then the system bled. We try to finish each system individually to avoid leaving bolts or lines loose. We finalize the brake system by bleeding them to avoid a disaster. Fuel and coolant hoses should be connected before a final check of all systems.

Always check all fluids before making any attempt at starting the engine for the first time. Make sure that the automatic transmission selector cable is adjusted properly (if equipped) before starting. If, for instance, the selector cable is out of adjustment at the transmission, the engine will start and the transmission will be in reverse. This happens more often than you might believe. Worse yet, if the transmission is not full of fluid, when you add the final few quarts with the engine running, the transmission goes into reverse with you chasing the car.

Once the engine is running, top off the fluids and let the engine run until the thermostat opens and recheck the coolant level. Check the feel of the steering, is it tight? Does the brake pedal feel firm? What about the emergency brake; does it feel tight stopping after about 15 to 17 clicks on the ratchet locking mechanism? Try putting the transmission in gear; do you feel a bump going into reverse and drive? If the trans goes into gear OK, go back and forth between forward and reverse a few times. Go out and check the transmission fluid level and add if necessary. If you have a manual transmission, does the clutch feel correct with 1½ to 2 inches of free-play at the clutch pedal? If the free-play is correct, try putting the trans in gear and slowly letting the clutch out. Does it engage smoothly? Check the ground for any fluid spots. If not, we are very close to that first drive to test all our major work.

The Road Test

The first road test should be about checking the feel of the brakes and steering first. Take off easy and apply the brakes. There should be a full pedal, with plenty of stopping power. The steering should be tight with no major pull if you put the shims back close to where they were. If all goes well, the next trip will be to the alignment shop and then a Saturday night cruise.

No matter how careful you are, there will be a few minor glitches to take care of on the first few road trips. Don’t feel bad, as that is common when you do any major restoration like this. We make sure the owner understands that we will take their Corvette on a long road test to avoid as many surprises as possible. Once we have any minor issues resolved, they receive the car. This avoids any hard feelings after major service work is performed. The feeling of a properly restored, upgraded chassis is unforgettable and now, you can go out and enjoy!





1 Shorty headers are installed with Earl’s pressure master header seals. These header seals really work for 100,000 miles without blowout. Header bolts don’t require frequent tightening either.

2 We decided to reseal the A/C components while we had the chance. Our A/C plenum evaporator case assembly can be installed later, but it sure is easier when the chassis is out of the way.

3 This line-up tool is used to align the chassis to the body on the passenger side sill. There is another line-up hole in the body and chassis on the driver side at the front of the door sill. Both line-up holes in the body have red plastic plugs in them.

4 The body mount rubber cushion and bolt is installed now that the chassis and body have been aligned. We tighten the bolts after all the cushions and bolts are installed and threaded at least three or four turns.

5 Now we can put all the bumper crash pieces in place using new hardware. We disassembled all the rear bumper impact components to clean and paint them. This is where a photo can be very helpful with the multiple pieces involved.

6 Almost looks like a complete Corvette again. The rear bumper cover is installed and adjusted to fit the body lines.

7 The underside has the positive battery cable installed after removing it for checking length. You can see how tight this area is. The sooner this cable is installed, the better.

8 We used an aftermarket crossmember for our 700R4 overdrive transmission upgrade. It is necessary to move the emergency brake pulley to avoid driveshaft contact.

9 The crossmember is really helpful in many ways, allowing ample room for just about any exhaust system we choose. We used stainless steel fuel and brake lines for long life. Using stainless steel will also prevent fuel line internal corrosion from the ethanol in the fuels we have in use today.

10 We wanted to be able to shift our overdrive transmission into first gear, so we replaced our original detent on the shifter.

11 Our new electric cooling fans will be powered at the starter using a fuse link for protection. Once we fit all the wires, they will be covered with black plastic wire loom. The shorty headers allow plenty of clearance around the starter, keeping heat away.

12 We’re ready to install our rear exhaust hangers on the Magnaflow mufflers. We decided to use a complete 2½-inch diameter exhaust system from headers to mufflers for easy installation.

13 The radiator, shroud and cooling fans are a complete unit and like the exhaust, drops in place of the original pieces. Our new Blueprint engine will be adequately cooled with this assembly even when the A/C is on in the hot summer months.

14 For our ride to the alignment shop, we are installing equal amounts of shim at the trailing arm. Don’t forget to install at least enough shims to keep the trailing arm from moving side to side. You’ll have the scariest ride of your life when you accelerate and let off the throttle if you don’t.

15 Chip Foose wheels allow plenty of room for the upgrade to Wilwood calipers and drilled rotors. Michelin Pilot Sport A/S tires will make a smooth high speed ride when we are cruising in overdrive.

16 We were hoping to wrap up our project but we encountered this previous accident damage. All the front fender reinforcements were loose. Some were completely broken loose, like this one. We used 3M product 8115 to bond all the reinforcements then we’ll smooth it off for painting around the edges.

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