Installing a Corvette Suspension
1. The front crossmember comes fully welded as a unit along with separate upper shock mounts, boxing plates, and the necessary hardware.
2. We are installing '87 Corvette pieces but kits are available to use suspensions up to '95. Be sure to get the entire suspension assembly because almost everything is going to be reused. A company like J&D Corvette will have everything you'll need.
3. Before we started anything we made sure that the frame was
square and had not been tweaked or bent out of shape. Mike and Bob
measured side to side front to rear on both sides, and in an X, from one
side to the other from several different locations using crossmembers and
rivets as reference points. If your frame is more than 1/8-inch out of
square, the frame should be properly straightened before proceeding.
4. Before removing the original suspension, scribe a vertical line on the frame to locate the stock axle center-line. Using the axle snubber holes as a reference point isn't recommended, as these holes can vary as much as 1 inch from true center. It is important that the front wheel visually looks centered in the wheelwell, especially on '53-56 ford pick-ups, the front wheel was too far to rear to properly center it in the fender opening, and lowering only exaggerates this situation. In this frame's case the snubber hole was centerline.
5. Flat Out Engineering recommends moving the front axle
centerline 1 to 2 inches forward from the stock centerline depending on
the wheel and tire diameter used. If the cab is still mounted on the
frame, hang the front sheetmetal and mock-up the wheel and tire combo to
determine the proper front-axle centerline location. Mark this location
on the framerail. Mike moved the centerline forward 1 ½ inches.
6. It is now time to get the boxing plates ready to be tack-welded. Since the edge of the upper and lower framerails were not straight Mike used a straight edge to mark the rails to allow the boxing plates to fit flat.
7. Using a plasma cutter and then a grinder Mike got the edge
straight enough to fit the plates. The boxing plate should be slightly
shorter in height than the framerail surface so that you are filling in
a small "L" shaped weld surface at both top and bottom. If the boxing
plate is the same height as the frame rail, you are not getting the proper
weld fill, and you will grind most of the strength away when you do your
finish grinding. If the top or bottom rails are not 90 degrees to the
sides of the rails, tap them up or down as necessary, or grind a little
off of the boxing plates to allow this proper fit for welding.
8. Mike placed the boxing plates on the inside of the framerails and tack welded them. You don't want to weld them solid at this time. It's better to wait until you determine the final correct location of the new crossmember.
9. The Corvette front spindle center is 5/16 inch behind the
ball joint and spindle upright center. That means the center of the
wheel is 5/16 inch to the rear of the center of the new crossmember.
So the spindle (not the crossmember centerline) will locate on the frame
centerline (vertical line you scribed on your framerail). The easiest
way to do this is to mark a vertical line on the center of the upright
portion of the new front crossmember on each side and then mark another
vertical line on the crossmember upright 5/16 inch to the rear of the
crossmember centerline. This is your spindle centerline or the center
of the wheel when installed.
10. Mike slid the crossmember up from underneath the frame and positioned it by lining up the spindle centerline mark (rear most line on the upright) with the framerail centerline using a small square. Make sure you get this right, it will determine how well the wheels will look in the fender openings.
11. The crossmember should be sitting level with the ground when
the truck is at ride height. Bobco has found that with the frame sitting
level the crossmember should be set approximately 2 to 3 degrees lower
in rear than the front to duplicate the most common installation when
using front tires and larger rears. Most people use a 25- to 26-inch
tall front tire and 28- to 29-inch tall rear tire. Measure your wheel
and tire combinations and base your ride height and frame angle on that.
If you're using the same size tire all around place the crossmember
level. Mike determined this angle by placing a magnetic angle finder
(protractor) on the top of the center of the crossmember.
12. The front crossmember should be level at this point and the tubular lower control arm mounts should be horizontal when the frame is at ride height. After double-checking everything again Mike tacked the crossmember in place.
From "Independent Thinking" Writen by: Kevin Lee , Classic Trucks Feb 2003; Vol 12. No 2