The venerable Jeep Cherokee is often lauded for its practicality, off-road prowess, and ease of maintenance. One of the key features that sets it apart from its contemporaries is the use of its solid front axle, a feature that enthusiasts adore due to the ease of modification and swaps that further increase its capabilities. The solid front axle is attached via a 4-link suspension setup located by a track bar and sprung via coil springs, this is where issues start to arise. A 4 link setup when used in a “leading link” configuration is inherently unstable, a problem that many Jeepers will discover when suspension components start to wear out, most notably the track bar. The instability manifests itself through a phenomenon known as “death wobble”. A separate but often related issue is known as bump steer which occurs when the travel arc of the drag link (steering link) and track bar are mismatched. This can be felt with a jolt in the steering wheel or as unintentional steering when driving over a bump. Bump steer can affect all suspension types, but is more pronounced on solid front axle vehicles for reasons which will become apparent later in this article. Solid front axles have a number of other disadvantages, such as non-adjustable camber, high unsprung weight, and relatively limited caster adjustment - all issues that wouldn’t matter on a normal Cherokee.
Stock solid axle
When high speed stability becomes the main goal, the Cherokee’s solid front axle becomes a hindrance. When I started racing my Cherokee, the need to address the front suspension setup quickly became apparent. On more than one occasion when letting off the throttle at the end of the run the front end became unsettled and threw the Jeep into a brief wobble - a scary thing at 130mph! With no chance of slowing down, I decided to convert the Jeep to an independent front suspension setup, but with one condition: It must maintain its 4wd. Jeeps and many other solid axle vehicles have been converted to IFS in the past. There are even off the shelf fabrication kits that give you all the components you need with proven geometry. It is rare to see an IFS conversion that incorporates the drivetrain components necessary to maintain 4wd. It became my goal to do so while making minimal modifications to the existing frame rails on the Cherokee, and creating a removable subframe to house the differential, steering and control arms.
Liberty Dana 30 IFS front diff in place
Starting with a blank canvas, I had to build a subframe to hold all the components. I chose to use 1.5” x .134 wall mild steel tubing due to having a surplus of the material and the ability to bend it. This tubular frame attaches to the Cherokee’s unibody via bolted joints at the factory lower control arm mounts, the driver and passenger track bar mounts, and the sway bar mounts. Now I had to decide what drivetrain and suspension components to use. From the day the whole idea popped into my head I knew I wanted to use the KJ Liberty Dana 30 IFS differential. The KJ D30 uses the same differential carrier, ring and pinion size and spline counts as the existing XJ solid Dana 30, so I knew it was strong enough for what I was throwing at it. It’s also made of aluminum, making it quite light. The next component I had to choose was the uprights, or knuckles. Originally the stock solid axle Dana 30 knuckles were mocked up, but it was quickly apparent that upper control arm geometry would be difficult to optimize due to how short that knuckle is, and my ultimate decision to use the factory frame rail as the mounting point for the upper control arm.
As a mechanic, I have experience working with tons of different vehicles and front suspension work is guaranteed any day of the week, so I had plenty of other ideas on what knuckles might be appropriate. I decided to pick up a knuckle from a 2008 Jeep Liberty because it is tall, ball joints are cheap and readily available, and its made of aluminum. Having the front diff mocked up in the truck I stuck a solid steel alignment bar through the diff and hung the knuckle off the end of it. I ended up with the lower control arm perfectly flat from the knuckle to the subframe, and the upper control arm able to be mounted with quite a bit of freedom while still landing within the bounds of the factory frame rail. The control arms are not borrowed from any existing vehicle, they are built specifically for this project. The lower control arms are fabricated from .125 flat plate tig welded together forming a c-channel cross section. They are attached to the subframe via 5/8 heim joints. The mounts have multiple positions to bolt the control arm in to adjust roll center. The upper control arms are fabricated from .25” plate and attach to the frame via 5/8” and 1/2” heim joints. The upper control arms are designed in a way that minimizes the influence of caster adjustment on camber change. The steering rack is a manual Pinto style rack, which is one of the most popular units for hot rods and race cars.
Solid alignment bar simulates the steering knuckle at ride height.
Upper and Lower control arms in place
Steering rack in place
Completed structure
Optimizing tie rod height and length for minimal bump steer.
Making adjustments to the suspension proved to be fairly simple, since all joints have a heim joint at each end. The most difficult task in the setup was minimizing bump steer. Since the steering gear had to avoid the front differential, the rack had to be placed high and quite far forward. This positioning resulted in anti-ackermann steering geometry and the need for spacers to elevate the tie rod ends to reduce bump steer. The anti-ackermann geometry results in poor low speed maneuverability, but, from what I have read, greater high speed cornering grip – not something I was looking for, but not detrimental either.
Recording camber curve and bump steer
Front suspension and drivetrain can be removed in one piece for engine service.
Now, what would I change if I had to do it all over again? Well, one of the major design challenges was dealing with the effects of the control arms being so short. Narrowing the subframe would allow for longer lower control arms. The upper control arms would either have to be mounted above the factory frame rails to move the mounts further inward, or they would have to be recessed in pockets inside the frame rail. I feel that my choice in front driveline components was appropriate, as anything stronger would’ve been heavier. At 540whp, the Dana 30 IFS is holding up to both trans-brake launches and a massive amount of midrange torque, though, torque steer is considerable.
See more images of the build HERE