CORVETTE SUSPENSION FOR CHEVY ADVANCE DESIGN TRUCKS

Updating A 1947-54 Chevy Chassis With Flat Out Engineering IFS

By Ron Ceridono   –   Photography by the Author

Like most manufacturers, as World War II came to a close, Chevrolet resumed production of cars and trucks with what were essentially prewar designs. Chevy’s AK series was introduced in 1941, continued in 1942, but wasn’t available to civilians again until 1946 (from 1943-45 GM continued to build trucks for the military).

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02 Paul Wilson and Merissa Ceridono cross measured the Chevy’s frame and found it to be 5 16 inch out of square
Paul Wilson and Merissa Ceridono cross measured the Chevy’s frame and found it to be 5/16 inch out of square—that would have to be addressed before going any further.

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In 1947 Chevrolet introduced what is arguably one of their best styling efforts, the new Advance Design series trucks with what was called the Unisteel cab. The series remained in production with minor alterations through 1953. In 1954, some noticeable changes occurred, including a one-piece windshield and a new grille. For the first part of 1955, other than some new emblems and the elimination of the torque tube driveline, not much changed until the all-new Task Force series was introduced. As a result, these trucks are usually referred to as the ‘54/first series ’55 style while second series is used to describe new ’55 design.

03 In between all the crossmembers the results weren’t encouraging but at least they were consistent
The frame was measured diagonally from end to end. In between all the crossmembers the results weren’t encouraging, but at least they were consistent.

Advance Design Chevy trucks are a hot commodity and Paul Wilson was fortunate enough to come across the near-perfect ’52 Chevy truck cab and front sheetmetal; unfortunately the frame was beyond saving. As luck would have it, a ’54/first series ’55 frame was found and the price was right but there were still issues to resolve, which we will explain.

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04 To square the frame it would be necessary to remove the crossmembers
To square the frame it would be necessary to remove the crossmembers. That process began by centerpunching the heads of all the rivets holding the crossmembers in place.

To update his truck Wilson decided to install C4 Corvette front and rear independent suspension with components from Don McNeil’s Flat Out Engineering. McNeil is a true hot rod pioneer who has been involved as a drag racer, Bonneville competitor, award-winning car and truck builder, as well as a businessman. Today McNeil specializes in kits to install ’84-96 Corvette C4 front and rear suspension components under an array of Chevy and Ford cars and trucks. These kits maintain the correct geometry and handling characteristics C4 Corvettes are known for and are designed to be easy to install. They come with all the hardware required and detailed instructions.

05 Before the crossmembers were removed angle iron braces were welded to the rails to prevent them from spreading apart
The heads of the rivets were then drilled. Before the crossmembers were removed angle iron braces were welded to the rails to prevent them from spreading apart.

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Like the Advance Design Chevy trucks there were two versions of the C4 Corvette suspension systems. McNeil tells us the ’84-87 Corvette front suspensions are approximately 1 inch narrower at 61 inches than the ‘88-96 versions; ‘84-87 front suspensions have 11-inch front brake rotors, so most 15-inch will fit; ‘88-96 front suspensions have 12-inch front rotors so 16-inch or larger wheels must be used. In the rear, ‘84-87 suspensions are  61 1/2 inches wide, wheel flange to wheel flange, and used parking brakes inside the rotor hats. The ‘88-96 is 1 inch wider at 62 1/2 inches and the parking brakes are built into the caliper. Both series use the 5-on-4.75 wheel bolt pattern, forged aluminum spindle uprights, A-arms, half shafts, and control arms that are not only lightweight but incredibly strong. These lightweight aluminum components give the suspension system a sprung to unsprung weight ratio that is unsurpassed.

06 After the heads of the rivets were drilled an air chisel was used to knock them off
After the heads of the rivets were drilled an air chisel was used to knock them off.

A critical part of installing any suspension component is making sure the frame is a solid foundation to build on—ours was not. When cross measuring our frame (from left front to right rear and right front to left rear) we found it was 5/16 out of square—1/16 is considered to be the maximum deviation. The frame showed no sign of damage so we assumed it left the factory that way, but regardless of the cause it had to be fixed.

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07 With the heads of the rivets removed the remaining portions were knocked out with a punch
With the heads of the rivets removed the remaining portions were knocked out with a punch.

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To resolve the problem with the frame we removed all but the very rear crossmembers as it wouldn’t budge with them in place. Removing the crossmembers did two things, it made the frame limber enough to make it square. It also made it possible to push the front of the frame rails together, put the Flat Out Engineering crossmember in place then spread the frame apart so the notches that were previously cut fit around the uprights of the C4 crossmember without cutting off the frame horns. Once square the original crossmembers were replaced by an X-member from Progressive Automotive. All things considered, particularly with a frame that is square with the stock crossmembers, remain in place, it would be quicker and easier to cut off the frame horns as the Flat Out instructions show.

08 Our original plan was to place the frame rails on lengths of rectangular tubing but decided against it
Our original plan was to place the frame rails on lengths of rectangular tubing but decided against it. Instead we clamped the rails to the legs of the hoist.

Next time around we’ll show how to rebuild and install the front suspension components followed by installing the C4 Independent Rear Suspension. It’s all part of our independent thinking.

09 Using washers as shims on the hoist arms the frame rails were leveled side to side and set at a 2 1 2 degree angle to simulate the truck’s nose down rake at ride height
Using washers as shims on the hoist arms the frame rails were leveled side to side and set at a 2 1/2-degree angle to simulate the truck’s nose down rake at ride height.
10 Flat Out Engineering’s instructions for positioning the front crossmember are easy to follow
Flat Out Engineering’s instructions for positioning the front crossmember are easy to follow. Note the precaution that the lower control arm mounts should be level.
11 We taped the frame rails so our layout lines would be easy to see
We taped the frame rails so our layout lines would be easy to see. Here Wilson establishes the spindle centerline on each side while Buddy the wonder dog guards the door.
12 Notches have to be cut in the frame rails to accommodate the Flat Out Engineering front crossmember
Notches have to be cut in the frame rails to accommodate the Flat Out Engineering front crossmember. They were laid out to tilt the crossmember back 2 1/2 degrees to keep the control arms level.
13 When the notches were cut the portions with the Xs were removed leaving small strips of the ’rails intact
When the notches were cut the portions with the Xs were removed, leaving small strips of the ’rails intact.
14 The 4 inch wide notches in the frame rails were carefully cut with an abrasive wheel
The 4-inch-wide notches in the frame rails were carefully cut with an abrasive wheel. The goal is to make a tight fit between the crossmember and the ’rails.
15 This is the completed cut on the passenger side frame rail—we didn’t cut the frame horns off for the reasons outlined in the text
This is the completed cut on the passenger side frame rail—we didn’t cut the frame horns off for the reasons outlined in the text.
16 In normal circumstances cutting off the front of the frame with the stock crossmember left in place is the easiest way to install the Flat Out Engineering crossmember
In normal circumstances cutting off the front of the frame with the stock crossmember left in place is the easiest way to install the Flat Out Engineering crossmember. Our circumstances weren’t normal.
17 With the frame verified as level side to side and nose down 2 1 2 degrees the new crossmember was positioned and tack welded in place
With the frame verified as level side to side and nose down 2 1/2 degrees the new crossmember was positioned and tack welded in place.
18 To pull the frame into square we used a pair of pipe clampsTo pull the frame into square we used a pair of pipe clamps
To pull the frame into square we used a pair of pipe clamps. Once squared additional diagonal angle iron braces were then added to hold the frame rails in place.
19 Rather than reinstall the original crossmembers we opted to install a tubing X member from Progressive Automotive
Rather than reinstall the original crossmembers we opted to install a tubing X-member from Progressive Automotive. Prior to installation the frame rails were boxed.
20 The Progressive Automotive X member is a universal design that has to be trimmed to fit
The Progressive Automotive X-member is a universal design that has to be trimmed to fit. The frame may be boxed just where the X-member attaches to the frame, or as we did the entire length of the ’rails.
21 With the X member centered in the frame and located the proper distance from the front spindle centerline it was trimmed to fit
With the X-member centered in the frame and located the proper distance from the front spindle centerline it was trimmed to fit.
22 The frame rails were once again checked to ensure they were level and square then the X member was tacked in place
The frame rails were once again checked to ensure they were level and square then the X-member was tacked in place. All dimensions were checked again before the final welding was done.
23 Before the final welding was done on the Flat Out Engineering crossmember the drop of the frame horns was checked to ensure it was 3 1 8 inches from the top
Before the final welding was done on the Flat Out Engineering crossmember, the drop of the frame horns was checked to ensure it was 3 1/8 inches from the top of the frame rails.
24 A final measurement was made to make sure the frame horns were square
A final measurement was made to make sure the frame horns were square. Once that was confirmed the new C4 crossmember was welding in place.
25 At this point the frame is square the X member is in place and the Flat Out Engineering crossmember is installed
At this point the frame is square, the X-member is in place, and the Flat Out Engineering crossmember is installed.
26 The next chore is to clean and rebuild the front and rear suspension from the donor ’86 Corvette
The next chore is to clean and rebuild the front and rear suspension from the donor ’86 Corvette.

Sources
Flat Out Engineering
(714) 639-2623
flatout-engineering.com

Progressive Automotive
progressiveautomotive.com

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