Ford F150: How to Solid Axle Swap a 4x4

This operation replaces the stock 1/2-ton independent front suspension (IFS) axle commonly known as TTB (Dana Twin Traction Beam) with a solid or straight axle from an older 1/2-ton truck or Bronco.

By Timothy Savage - July 13, 2016

This article applies to the 4WD Ford F-150 (1980-1997).

While the whole point of an independent front suspension was ride comfort for the driver and passengers, 4WD “true believers” are of the opinion that the point of being able to add drive power to all four wheels is for driving up and down steep hills in muddy conditions. In lieu of comfort, this requires a strong, stiff axle on both ends, high ground clearance, and optimum wheel travel. And many believe that can best be accomplished with a solid axle on the front, as well as the rear.

The F-150 used TTB independent front suspension axles with coil springs on 1980 to 1997 model year 4x4s, which comprised three F-150 generations:

  • Seventh generation (1980-1986)
  • Eighth generation (1987-1991)
  • Ninth generation (1992-1997).

The 1979 was the last year F-150s and F-250s that had actual solid front axles. Ford carried its TTB front end forward for 16 years in the 1/2- and 3/4-ton truck (and six years in the 1-tons). For the tenth generation F-150 (starting in 1998) Ford replaced the TTB front axle in the F-150 with a new A-arm suspension, and even though the F-250 returned to a solid axle in 1999, the F-150 never looked back at one again.

Ford F150: How to Solid Axle Swap a 4x4

Materials Needed

  • Ratchet set
  • Sockets
  • Breaker bar
  • Grease gun (with high-temp wheel bearing/disc brake grease)
  • Hammers (big, bigger, biggest)
  • Pry bars
  • Anti-seize lube
  • Brake cleaner
  • PB Blaster
  • Two-jaw puller or pickle fork and Pitman arm puller
  • Torque wrench

The most desired SAS model year donor vehicles for 1980 to 1997 F-150s are the 1978 and 1979 model year D44 (the “D” stands for Dana) solid axles. They are considered the “holy grail” of F-150 SAS for their typically higher price, which is based on the two reasons they offer a more straightforward conversion:

  • The housing dimension on the 1978 to 1979 axle will give you a lot of room on the driver side for control arm mounts (later year F-250 and F-350 solid axle housings can be made to work, but will will give you much less room under the front end), and
  • The 1978 to 1979 front axle disc brake setup makes for a more straightforward build, especially since the brake calipers from your current TTB axle will not fit on the older solid front axles.

Note that these older axles also typically come from well-used (or maybe abused) vehicles, and may have to be entirely rebuilt before being “swappable.” The differential gearing may also have to be replaced, due to its worn condition, or—importantly—to set its gear ratio the same as your truck’s rear end ratio (or vice versa).

Also note that there will be some metal fabrication and welding involved, as well as some steering/suspension geometry work. Many aftermarket auto supply companies make compatible upgrades for raising and modifying a Ford F-150, some of which may also come in handy for a SAS. Depending on what you want (or end up needing) to do, you can search them out for:

  • Mount connection plates/brackets,
  • Shock towers,
  • Spring buckets,
  • Extended radius arms, and of course,
  • Springs.

Preparation

For the solid front axle swap, the truck must be lifted at least four inches by using taller coil springs. This isn’t so it can use bigger tires; although that certainly is a desired side effect for many 4WD owners (a note on tire size later), but so the axle will fit below the engine and front crossmember. But because this vehicle height increase also results in the front axle having more travel, two important modifications must be made:

1. Radius Arms: Either extensions from the radius arm ends from the frame or longer radius arms mounted further back on the frame will be necessary. Some go with extending the original radius arms, while another option is using the longer radius arms that came with the solid axle. In addition, custom longer radius arms are available from aftermarket suppliers.

ford f150 SAS solid axle swap change bronco F250 how to DIY guide info
Figure 1. Radius arms with extension on back.

2. C-Bushings: Additional axle travel also means the axle now rolls forward a bit more when it moves upward, putting forces on the wheel to make it want to go under obstructions, rather than over them (over being the more desirable outcome, obviously). Polyurethane C-bushings are available in different “degree” castings designed to rotate the axle a small amount backwards to set the axle to the castor that you’ll need to keep the drive shaft and pinion as straight as possible. Be sure to get the bushings installed right: They will say on them “FRONT BOTTOM - 4 DEGREE OFFSET.” For the four-inch lift used in this article, 4-degree C-bushings will be used.

ford f150 SAS solid axle swap change bronco F250 how to DIY guide info
Figure 2. Red C-bushings installed.

You will need high enough jack stands, and at least four, to drop the TTB front axle and replace it with the solid axle. Get two jack stands under the front axle as close to the front bumper as you can get. The reason to have the vehicle level during the solid axle installation is because the wheels will need to be able to drop for alignment, which will be shown later.

ford f150 SAS solid axle swap change bronco F250 how to DIY guide info
Figure 3. F-150 on jack stands near front bumper.

At this point, we will assume that you have your truck up in the air, and safely set on jack stands. Pull the wheels off now.

Step 1 – Remove the TTB axle

Disconnect and remove the:

  • Antilock sensor from the back of the wheel
  • Stabilizer bar and tie rod ends
  • Steering assembly/drag link from Pitman arm
  • Track bar
  • Brake lines (cover/plug the line ends)
  • Disconnect the shock bottom retainers
  • Disconnect top spring retainers
  • Lower the axle
  • Disconnect the lower spring retainers and remove the springs
  • Disconnect the radius arms, and then
  • Pitman arm joints.

Lower the TTB axle to the floor, and move it out of the way.

Step 2 – Hang the solid axle

You can use the original TTB upper coil spring buckets, as shown, or use 1978 to 1979 upper buckets, which can be located a bit further forward for a better approach angle and more clearance from the crossmember. The DIY shown used a plumb bob to mark where the bottom of the springs would be directly below the top attachment point of the springs, as they might not want to hang straight down.

Attach the new springs to the solid axle with the spring retainers.

Lift the solid axle, compressing the springs, until the axle is at its ride height.

Warning

Lifting the solid axle must be done slowly and carefully, watching the two sides of the vehicle to make sure it doesn't fall off the jacks and causing damage or serious injury.

ford f150 SAS solid axle swap change bronco F250 how to DIY guide info
Figure 4. Lift the solid axle from beneath, compressing the springs.

With the springs compressed to their drive ride height, line up the radius arms and brackets on the frame and square everything up, making sure the brackets are in the same relative position on either side. You’ll want the radius arms to be parallel to the ground to allow optimum up/down movement. Lifts over the 6-in will require using either longer radius arms, or drop brackets. Even using the radius arms from a 1978 to 1979 front axle, the radius arm brackets will have to be moved to a different position on your frame.

Mark where the bolt holes go into the frame, drill them, and bolt the brackets in place.

ford f150 SAS solid axle swap change bronco F250 how to DIY guide info
Figure 5. Move the radius arms into position, mark the bracket holes, drill them out, and mount.

Once the radius arms are bolted down the truck can hold its own weight up front, but jack stands kept under, the frame can keep any unexpected movements from happening.

With the wheels off, mount the shocks and brake lines, and bolt the drive shaft back together. If the pinion yoke on the front differential doesn’t match-fit to your front drive shaft, you will need to swap it out with the pinion yoke from your TTB front axle. Tighten the universal joint’s bolts to only 12 lb-ft (16 Nm).

Step 3 – Set up your steering and track bar

The track bar helps to keep the front axle under the truck when the steering and suspension is moving and flexing. The track bar and drag link of the steering system have to be as close as possible in length—and as close to parallel with each other as possible. Lifting your vehicle doesn’t necessarily mean you will have to use a drop Pitman arm. Hold off on that until after you line everything up.

Do so by making sure the axle is square and centered under the truck. Then bolt up the tie rod and drag link. Measure the length of the loose end of the drag link to find a location for the bracket you’ll be fabricating to allow the track bar as close to the drag link as possible, as well as as close to the angle of the drag link as possible. Then build the track bar and bracket to accommodate these criteria. This end of the frame is boxed, so many simply weld a simple bracket they’ve fabricated to the frame.

ford f150 SAS solid axle swap change bronco F250 how to DIY guide info
Figure 6. Track bar bracket fabricated and welded to frame.

The preferred track bar build material is DOM tubing (DOM is Drawn Over Mandrel steel tubing produced from welded strips of C1020 steel). Long nuts are welded to the end of the tube, with threading to adjust a Johnny Joint—a bushing joint. (This is also true for fabricated tie rods and drag links.)

ford f150 SAS solid axle swap change bronco F250 how to DIY guide info
Figure 7. Johnny Joints connected to DOM tubing for track bar fabrication.

Factory track bars typically have a curve to them to clear frame components. For a straight track bar fabrication to clear the crossmember, you may have to cut the front of the engine support crossmember off and reinforce the remainder.

ford f150 SAS solid axle swap change bronco F250 how to DIY guide info
Figure 8. Trimmed crossmember.

Attach the track bar and then double check to make sure everything is still square, centered, and aligned.

Step 4 – Finishing up

When completed with this:

  • Reconnect the ABS sensors and brake lines.
  • Put the wheels back on, lower the truck to the floor, and get it to an alignment shop ASAP, remembering to have them align the vehicle to the 1978 F-150 4x4 specifications, not the specs for your vehicle’s model year.
  • Test drive it, and make any necessary adjustments.

You're done. Of course, you’ll probably have to now raise your tired rear end to match the level of your now-raised front SAS end.

A Not About Tires

With a D44 solid axle upgrade resulting in some additional suspension lift, some drivers go wild with “big foot” tires. But generally speaking, a stock D44 TTB axle should only be expected to handle up to 35-inch tires for serious off-roading, with a D44 solid axle being able to handle up to 39-inch tires for serious off-roading. For anything bigger than 40-inch, experienced off-roaders will point you toward a D60 solid axle.

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