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There is good news when it comes to removing an old front suspension and replacing it with a more modern suspension. The aftermarket street rod industry has had many years to design and produce replacement units that far exceed the performance of the older original suspensions.

The bad news is that if the installation of the new suspension isn’t done correctly, the vehicle being modified may actually drive and handle worse than it did with the vintage front suspension. The lesson here is, if you are considering such an undertaking, buying new parts doesn’t guarantee a job well done. For that you will need to gather all the information you can find concerning how a suspension works before ever turning a bolt on the old suspension to remove it. Where do you find such information? This book is a good place to start. After that, visit the local front end alignment store, where you can talk to the tech about what you are doing. His time costs money. Pay him.

THE PROJECT’S NEW SUSPENSION

The front suspension I’ve chosen for this project is known as an IFS, or independent front suspension. It is also known as the Mustang II front suspension because it is basically an improved version of the original Mustang II front suspension. In the restoration world, this front end is also known as an SLA suspension, or short arm, long arm suspension. Short arm means the upper control arm is shorter than the lower control arm, as shown in photo 1. OK, I know this is going to come up, so here goes. The upper control arm is shorter because this setup acts to keep more of the tire on the road at all times, especially when cornering, and that greatly improves upon the handling qualities of the vehicle.

This type of replacement front suspension consists of three main components: a front cross member, shown already welded into place on the frame in photo 2, and the right and left upper control arm mounting brackets, at this point only tack welded to the frame.

Photo 2 shows how the front cross member is positioned within the frame and how the upper control arm brackets are positioned on top of the frame rail, and it also points out a lot of other things that are going on at the same time.

PHOTO 1: A bird’s-eye view of an SLA front end. Notice how much shorter the upper control arm is than the lower control arm.

PHOTO 2: This is a finished view of the new cross member installation. Notice the new round tube at the front of the frame put there for cosmetic reasons, the dogleg created just aft of the cross member when the frame was narrowed, the new cross member itself, the upper control arm mounting plates, and, finally, the motor mount brackets. Phew! No wonder this took forever!

For instance, the frame has been narrowed to fit the new front cross member, the engine mounts have been tack welded into place, and the front tip of the frame has been cosmetically dressed out with a round steel tube. These are all steps that must be considered before ever opening the toolbox to start building a new front suspension.

These parts may be the guts of the new suspension, but in the overall scheme of things they represent only three pieces in a long list of parts that are needed to complete the transformation. Let’s take a look at the rest of the components that make up this IFS unit, and then I’ll explain some of the basics that make the IFS unit such a good choice when you are updating an older vehicle with a modern front suspension.

THOSE CUSTOM CONTROL ARMS

If you have ever had a disassembled front suspension, all of the parts in photo 3 will look familiar. With the exception of the control arms, which are custom-made tubular units, all of these pieces can be purchased off the shelf at the local automotive parts store. These are all Ford or Ford-compatible components and are as follows: disc brake rotors, disc brake calipers, spindles, coil springs, shock absorbers, and a power rack and pinion steering unit.

Did I say power steering? Yes I did. Recall that I said at the beginning of this project the goal would be to bring this car up to today’s standards and make it wife approved. Power steering is one of those requirements.

TIP

When adding the power steering option to an aftermarket IFS unit, be sure to ask the supplier about the source of the power rack and pinion unit. New power steering lines will be required, and you will need to know if the rack and pinion is from a Mustang, Pinto, or Thunderbird and the year model.

As for the custom tubular control arms, I elected to go with these parts to ensure that the front suspension on this car wouldn’t have that “borrowed from the salvage yard” look. Less expensive stamped-control arms are available, and they work just fine. Their only knock is that they look a little too factory to suit my taste.

FITTING THE NEW CROSS MEMBER

Referring back to photo 2, it is obvious that changes had been made to the frame to accommodate the installation of this suspension. To start, I had removed the bulky original cross member that supported the old front suspension as well as the smaller forward cross member located at the front tip of the frame. Both pieces had to go to narrow the frame to accept the new cross member. Why didn’t I just order a cross member that would fit my existing frame? I could have, but it would have taken several more weeks and hundreds more dollars to have the piece custom fabricated. Purchasing an off-the-shelf unit not only saved me a few bucks, it also allowed me to stay on schedule. And it affords me the opportunity to demonstrate how to narrow a frame correctly.

PHOTO 3: The IFS kit comes with just about everything, including the control arms, spindles, springs, shocks, brake rotors, brake calipers, and a power rack and pinion steering unit.

TIP

When ordering any IFS unit, particularly an off-the-shelf unit, make certain the supplier knows the year and model of the car in which the unit will be installed. This allows the supplier to provide control arms that are the correct length as well as coil springs that are the correct size, if they’re going to be installed.

SOME NIPPING AND TUCKING

The first step to narrowing any portion of a frame is to determine how much the frame needs to be narrowed. In this case, the original frame measured 26 inches wide at the old cross member location when measured from inside edge to inside edge of each frame rail. While I was at it, I also measured the width of the frame at the front tip. This point measured 29 inches wide from outside edge to outside edge. I’ll explain the need for this measurement later.

The replacement cross member measures 23 inches wide at the support flanges, where it welds to the inside of the frame rails. That’s a difference of 3 inches between the width of my new cross member where it mounts to the frame and the existing frame rails. This difference is the reason for the need to narrow the frame.

Now that I know the frame must be narrowed by a total of 3 inches to fit my new cross member, I divide that number in half to determine how much to narrow each rail: 1 1/2 inches.

ASSESSING THE RAILS

Making an observation of the frame rails before making any cuts tells me this frame is basically straight from just behind the old cross member forward to the front tip of the frame. That also tells me that any cuts I make should be made behind where the old cross member mounted and in the area where the frame begins to flare out as it widens and moves under the body of the car. This is preferable in that it lets me make my cuts and bends where anyone looking at the frame would expect to see bends and curves. It is the perfect hiding place.

MAKING THE FRAME PIE CUTS

Working with one rail at a time, my first step is to determine exactly where on the rail to make my cuts. I’ll start with the right rail. This isn’t rocket science, so I just eyeball the rail and pick my points. I make my first cut 18 inches back from the forward tip of the frame and the second cut 25 inches back.

Next, I make two full-scale templates of the rail area to be narrowed, one depicting the rail before being narrowed, the other depicting the narrowed frame using the proposed cut line points to make the bend in the rail. For clarification, I darken the proposed area of bend on both templates as shown in photo 4.

In the photo, the proposed areas of bend on the template were cut at 90 degrees. If I lay the protractor over the darkened areas and align it to the 90-degree cuts, it automatically gives me the precise angle to make my pie cuts in the frame rail in order to make the bends. That angle on both cuts is 10 degrees.

What is all this pie cut business? To bend the rail, I need to take a small wedge-shaped slice, or pie cut, out of the rail. This creates a gap in the sidewall of the rail so that when the rail is bent, the gap will close. Photo 5 offers a good view of how this wedge will be removed from the frame.

PHOTO 4: These templates depict the shape of the rail both before and after being narrowed. Notice the use of the protractor to determine the cut angles.

PHOTO 5: I taped the rail to help define the cut lines. Notice that the piece being removed resembles a wedge of pie, thus the name pie cut.

Since I’ll be bending the rail inboard at the rearmost cut, I want to take my wedge from the inside of the rail. I’ll use a reciprocating saw with an 8-inch metal cutting blade and remove my 10-degree wedge from the inner rail, allowing the cuts to taper to a point as they reach the outer wall of the rail.

For the second cut, I’ll bend the forward portion of the rail outboard. That means the pie cut will be made on the outside of the frame, and it will also be 10 degrees wide.

With both cuts made, all of the strength of the frame rail is gone, and it will bend quite easily. To control each bend, I use a ratcheting cable puller that is attached to the opposite side of the frame and to a point between the two cuts to pull the rail inboard until the rearmost pie cut closes.

With the ratcheting cable puller holding the rail bent into place, I use a hydraulic ram placed between the front tips of the frame to push the forward section of the frame back out until the second pie cut closes (photo 6). The rail now has a dogleg bend just aft of the position where the old cross member was located, with the front section of the rail being once again straight and parallel with the opposite, uncut rail. I’ll take measurements from the same points I used earlier to determine the precut width of the frame, and with any luck my new measurements will read 24 1/2 inches and 27 1/2 inches, respectively, exactly 1 1/2 inches narrower than before.

PHOTO 6: A ratcheting cable puller is used to bend the rail inboard at the rear-most cut, while a hydraulic ram is used to push the front section of the rail back out straight. I’ll know the rail is bent correctly when the pie cuts close.

PHOTO 7: The new cross member is positioned within the frame and leveled.

This is a time-consuming process, and the old adage of measuring two times, three times, and a fourth time if necessary is very good advice. When the rail is perfect, I tack weld both pie cuts, then repeat the entire operation on the other rail.

Once both rails have been cut, bent, and tack welded into place, it is time to once again check my measurements. Remember the 29-inch measurement across the front tip of the frame? This measurement must now read 26 inches. If it does, the frame is perfect, and the measurement at the cross member should read 23 inches. If it doesn’t, I must take frame cross measurements to see which rail is out of alignment.

I start by measuring from the first cut on the right rail to the tip of the left rail. That measurement must be 32 inches. If it isn’t, the rail must be moved either inboard or outboard, depending on the measurement, to achieve the 32-inch reading. When both rail cross measurements equal 32 inches, the cross member measurement reads 23 inches, and the front tip reads 26 inches, it is time for the cross member.

INSTALLING THE FRONT CROSS MEMBER

Because of my precise measuring, the new front cross member will be a snug fit between the two rails. I use a floor jack to push the front cross member up into place, then leave the jack there as a support while I again take measurements.

If you recall, I took some preliminary measurements of the old front suspension before removing it. One of those measurements was taken from the front axle centerline to a hole in the top of the frame 52 inches back. I again measure from that hole forward and remark my axle centerline on both rails at 52 inches, using a long straightedge laid across the width of the frame. This will be the centerline for the new cross member. Once centered on the new axle centerline, the cross member is first leveled, then tack welded into place (photo 7). Now the real work of building this suspension can begin.

THE BUILDUP

With the front cross member tack welded into place, I want to mock up the left side of the suspension minus the coil spring and shock absorber. Remember, I’m only tack welding things together for now; adding the spring would be dangerous and at this point unnecessary.

I start by clamping the upper control arm mounting plate to the top of the frame rail directly above the new front cross member, then bolt on the upper and lower control arms and the spindle. These are critical parts to setting the C and C of this suspension. What are C and C? Glad you asked.

C AND C: CAMBER AND CASTER

If this car ever hopes to roll down the road straight and true, I have to get the camber and caster alignment points perfect. To do that, I really need to know what camber and caster are and how each one will affect the handling of this ride.

The basic definition of camber is “the inward or outward tilt of the wheel when viewed from the front of the vehicle.” Here is an example: If a vertical line were drawn through the center of the wheel, it would be said to exhibit 0 degree camber. But if the wheel leaned inboard toward the engine from that same vertical line, the wheel would exhibit negative camber. On the other hand, if the wheel leaned outboard from that same vertical line, the wheel would exhibit positive camber. Improperly set camber causes excessive tire wear and allows the vehicle to wander all over the road.

Caster is defined as a “vertical line drawn from the ground up through the center of both the upper and the lower ball joints when viewed from the side of the car.’’ The vertical alignment of both ball joints means the vehicle exhibits 0 degree caster. Improperly set caster may cause a nonreturn of the wheel after a turn, vehicle drift, or a pull to one side.

Ask any front suspension specialist, and he will tell you a positive degree setting on both the camber and caster is a must. So with that thought in mind, the first thing I do is support the lower control arm by placing a jack stand under the arm, then level it using paint stir sticks as shims. This leveling action places the suspension at the assumed normal ride height of the car.

Next, I place the magnetic protractor vertically on the flat of the spindle and check for positive camber (photo 8). With the upper control arm clamped into place at the full inboard position on the mounting panel, my reading is 2 degrees negative camber. That’s a good thing. It means I’ve built into this front end a small amount of negative camber and a maximum 12 degrees positive camber, gained by moving the upper control arm full out-board. In a world where 1 to 2 degrees positive camber is ideal, everything is looking great.

To determine my caster setting, I place a 24-inch carpenter’s square just in front of the ball joints and measure the distance from the square to each ball joint (photo 9). In this case, the distance from the lower ball joint measures 3 inches, and the distance from the upper ball joint measures 3 1/16 inches. That’s perfect. My front end exhibits 2 degrees negative camber with plenty of positive degree adjustment, and my caster setting reads roughly 0.5 degree positive caster with plenty of positive degree adjustment available.

PHOTO 8: Notice that the upper control arm mount is only clamped into place. This allows me to move the mount if necessary to gain a positive degree reading on the magnetic protractor attached to the spindle.

PHOTO 9: With the upper control arm held full inboard, a measurement is taken at both ball joints to ensure their vertical alignment.

Had this measurement been, for example, 3 inches on the lower ball joint and 2 1/2 inches on the upper ball joint, I would have needed to move the upper control arm mounting panel back until the upper ball joint measurement read a minimum of 3 inches.

Now I can tack weld the left upper control arm mounting panel to the frame and repeat this exercise on the right side.

SOME STEERING CHECKS

The only things left to verify up here is the placement of the rack and pinion steering assembly and the spindle to rear axle alignment. I start with the rack and pinion steering assembly. All I’m looking for here is to be certain the tie-rod ends bend slightly downward and backward when mounted to the spindles. This will eliminate any chance of bump steer caused by the tie-rod ends having a forward bias. Any necessary adjustments can be made by adding shims where the rack mounts to the frame.

To check the spindle to rear axle alignment, I attach a string at the center point of the rear axle and extend that string forward through the center of the upper ball joint then beyond to intersect the center of the tie-rod mounting hole on the spindle, with the wheel pointing straight ahead. Also known as Ackermann, this setting is important, as it gives the front wheels the correct toe-out when making turns. If the string doesn’t intersect both the ball joint and the tie-rod hole, an alignment problem exists somewhere within the installation of the new cross member. Bring out the tape measure and double-check everything. As a last resort, consult your front suspension technician with hat and money in hand.

Once I know everything is set correctly—verified by having measured, measured again, checked, and checked again—the suspension components can be disassembled. The cross member, upper control arm mounting panels, and wedge plates can then be welded solid and ground smooth.

I didn’t mention installing the wedge plates? This triangular-shaped metal plate, referred to as a wedge plate, is included in the IFS kit and must be welded between the lower control arm mounting tube and the new cross member to prevent the control arm from flexing any time the car makes a hard turn (photo 10).

Worried about heat warpage during welding? That’s a huge concern. The remedy is to pick a point to begin welding, then weld a short bead, roughly 1 inch long, then move to another area of the frame and weld another short bead. Granted, this takes a lot of time, but this method works to keep the heat evenly distributed over the entire area being welded, thereby reducing the chances of heat warping any part of the frame. If necessary, a damp cloth will help cool the metal between welds, and a die grinder with a 5/16-inch-thick. 3-inch-diameter grinding wheel will make short work of smoothing the welds.

PHOTO 10: The triangular wedge plate must be welded to the lower control arm mounting tube for added reinforcement to prevent the control arm from flexing during a hard turn.