How To Do a Hack and Tap on a Jeep Cherokee XJ

If you have lifted your Jeep Cherokee XJ above three inches, there is a good chance you are dealing with driveline vibrations, binding on the trail, or a worn-out slip yoke. Instead of spending the money on a slip yoke eliminator kit or tearing into your transfer case, the hack and tap is a proven, cost-effective alternative. In this video, Spence from Core 4x4 walks through the entire hack and tap process on the shop XJ Cherokee using an Iron Rock Offroad kit and a junkyard front driveshaft.

Fitment: Jeep Cherokee XJ 1984–2001 (NP231 transfer case) | Also applicable to MJ Comanche

What Is a Hack and Tap?

A hack and tap is sometimes called the “poor man’s slip yoke eliminator.” The concept is simple: you cut (hack) the output shaft on your transfer case, drill and tap a bolt hole into the end, and bolt on a fixed yoke. This lets you swap your factory rear driveshaft for a front driveshaft from a junkyard XJ, giving you a double-cardan joint and moving the slip yoke down to the differential end of the driveline.

The result: smoother highway driving, no binding on the trail, and the performance of a slip yoke eliminator kit without the cost or the hassle of disassembling your transfer case.

Why You Need This on a Lifted XJ

When you lift a Jeep Cherokee XJ, the angle between the transfer case output and the rear axle pinion gets steeper. The factory rear driveshaft uses a single cardan joint and a slip yoke that slides in and out of the transfer case. As the angle increases:

• Highway vibrations — the slip yoke cannot compensate for the steeper operating angle, causing vibrations at speed
• Binding on the trail — when you flex out, the slip yoke can bind inside the transfer case, robbing you of articulation
• Wear and tear — the increased angle accelerates wear on the slip yoke seal and splines

Spence recommends the hack and tap for any XJ at four inches of lift or above. Below that, the factory driveshaft can usually handle the angle without issues.

The Iron Rock Offroad Kit

For this install, Core 4x4 used the Iron Rock Offroad hack and tap kit. What makes this kit stand out is the documentation — the instructions are thorough, and all the tools are available as add-ons if you need them. The kit includes:

• Fixed yoke — replaces the factory slip yoke on the transfer case output
• Retaining bolt with Loctite
• Optional drill guide — keeps your drill centered on the output shaft (highly recommended)
• Optional drill bits and taps — if you do not already own the right sizes

Transfer case compatibility: This method as shown works with the NP231 transfer case. If you have an NP241, you will need an additional seal kit from Iron Rock. The 231 is the most common transfer case in XJ Cherokees, so most builds will follow this exact process.

Why Use a Front Driveshaft?

On an XJ Cherokee, the front driveshaft already has a double-cardan joint and a slip yoke at the axle end. By using a junkyard front driveshaft on the rear, you get:

• Double-cardan joint — handles steeper operating angles without vibration
• Slip yoke at the differential — instead of inside the transfer case, the slip yoke now operates at the pinion where there is less angle change
• Low cost — a front driveshaft from a junkyard XJ costs a fraction of a custom driveshaft

If you are running a WJ, ZJ, or TJ, or if you want to do the hack and tap below four inches of lift, you will need a custom driveshaft made to length. The front-driveshaft method specifically works on XJ and MJ platforms with at least four inches of lift and a factory crossmember (no transfer case drop).

Step 1: Remove the Factory Rear Driveshaft

Start by getting the Jeep up on a lift or jack stands. Before you touch anything, soak all the pinion strap bolts with penetrating fluid. These are 8mm bolts, and they are easy to snap on an older Jeep. If you break one, you will be drilling and tapping even more than planned.

1. Unbolt the four pinion strap bolts at the rear axle
2. Slide the driveshaft out of the transfer case
3. Save your pinion straps and bolts — you will reuse them with the new driveshaft

Tip: It is easier to break the bolts loose with the transfer case engaged or with the Jeep on the ground. When the axle is drooped out on a lift, the pinion can spin freely and make it difficult to get the bolts off.

Before removing the driveshaft, take a look at the slip yoke angle. On this XJ at four inches of lift, the kink in the driveline is clearly visible. That angle is the root cause of every vibration and binding issue you feel on the road and on the trail.

Step 2: Measure for the Cut

This step must be done at ride height with the full weight of the vehicle on the axle. Set the Jeep back on the ground before measuring.

Measure from the center of the U-joint at the pinion yoke (or from the flat surfaces on the yoke) to the end of the transfer case output shaft. For a factory front driveshaft, the target measurement is 33-3/4 inches, with about 3/4 inch of variance allowed.

The Minimum Spline Rule

Regardless of your measurement, you must maintain at least 1-1/4 inches of spline after the cut. This is the minimum engagement needed for the new yoke to sit securely on the output shaft.

On the Core 4x4 shop XJ, the combination of a four-inch lift and a slight transfer case drop built into the long arm kit meant the measurement was tight. Spence went with the minimum spline measurement rather than the standard 33-3/4 inches. If you are above 4-1/2 inches of lift with a factory crossmember, you can follow the standard measurement.

Step 3: Cut the Output Shaft

Put the Jeep back up in the air for the cut. The single most important thing during this step is getting a flat, straight cut. If the cut is angled, your drill hole will be off-center, and the yoke will not seat flush against the end of the shaft.

• Use a cutting wheel or angle grinder
• Take your time — a straight cut now saves headaches later
• After cutting, clean up the end of the shaft and the splines so the new yoke slides on easily

Yoke Modification (If Needed)

On this build, the shaft was cut back far enough that the yoke plate was not seating against the end of the shaft. Spence trimmed the yoke back, which allowed it to slide an extra 3/4 inch toward the transfer case. This gave more room for the driveshaft and was especially important given the tight clearance from the four-inch lift and long arm kit drop.

Step 4: Drill the Retaining Bolt Hole

This is where the drill guide earns its money. You need a straight, centered hole drilled into the end of the output shaft.

With the Drill Guide

1. Slide the new yoke onto the shaft
2. Mark the center with a sharpie through the yoke bolt hole
3. Remove the yoke and center-punch the mark
4. Mount the drill guide and drill to the specified depth (about 1-1/8 inch per the kit, though this build went to 1-1/2 inch)
5. Use cutting fluid or WD-40 to keep the drill bit cool

Without the Drill Guide

If you did not order the guide, you can still do it:

1. Place the yoke on the shaft and mark through the bolt hole
2. Center-punch hard enough to give the drill bit a starting point
3. Match the angle of the output shaft with your drill as closely as possible
4. Drill slowly and check alignment frequently

Spence has done it both ways and says both work. The guide just makes it easier to get a perfectly centered, straight hole.

Step 5: Tap the Threads

Before tapping, use a slightly larger drill bit to put a small taper (chamfer) on the top of the hole. This helps the tap start straight and prevents cross-threading.

The Chip-Breaking Rule

When you are cutting threads inside a hole, material builds up in front of the cutting edge. If you do not break this chip, it can damage the threads. The technique:

1. Turn the tap forward two or three turns
2. Back it off half a turn to break the chip
3. Advance forward again
4. Repeat until you reach full depth

You can tap with a drill (go slow) or use a tap handle or socket for more control. If you are not experienced with a drill, the manual method is safer — it is much easier to feel cross-threading by hand than with a power tool.

Step 6: Install the Yoke and Driveshaft

With clean threads in the output shaft:

1. Slide the new yoke onto the splines
2. Apply red Loctite to the retaining bolt — this bolt is the only thing holding the yoke on
3. Torque the bolt to 30 ft-lbs
4. Bolt the junkyard front driveshaft to the new yoke using your saved pinion straps and bolts
5. Grease the slip yoke on the driveshaft before installing

Important: Use red Loctite on the retaining bolt. There is not a lot of force pulling on the yoke axially, but you do not want this bolt backing out. Torque it to 30 ft-lbs and let the Loctite cure before driving.

Step 7: Check Clearance at Ride Height

Set the Jeep back on the ground and check the slip joint on the new driveshaft. You need enough room for the driveshaft to compress during uptravel without shoving the output shaft into the transfer case — that will cause problems.

On the Core 4x4 shop XJ, the clearance was acceptable with the yoke modification that gave an extra 3/4 inch of room. Spence noted they would watch it during off-road testing, especially at full tuck.

Pinion Angle

With a double-cardan driveshaft, you ideally want the pinion pointed straight at the transfer case output. There is some room for variance. If your pinion angle is significantly off, you can add shims under the leaf springs to rotate the pinion up and bring it in line with the driveline.

Tools Required

• Floor jack and jack stands (or a lift)
• 8mm socket for pinion strap bolts
• Cutting wheel or angle grinder
• Drill and drill bits (sizes per Iron Rock kit instructions)
• Tap and tap handle (or drill with slow speed)
• Drill guide (optional but recommended)
• Torque wrench (for 30 ft-lb yoke bolt)
• Penetrating fluid (PB Blaster or similar)
• Red Loctite
• Cutting fluid or WD-40
• Center punch and hammer
• Tape measure
• Grease for the new slip yoke

Hack and Tap vs. Slip Yoke Eliminator Kit

Things to Watch For

• Transfer case drop: If your long arm kit includes a TC drop, factor that into your measurements. You may need to space the TC back up or use the minimum spline measurement
• Lift height: Below four inches, a front driveshaft will be too long. Above 4-1/2 inches is the sweet spot for this method
• WJ/ZJ/TJ: These platforms have a hardened output shaft, making it harder to cut and drill. A custom driveshaft may be needed instead of a junkyard front DS
• NP241 transfer case: Requires an additional seal kit — the NP231 method shown here will not work as-is
• Off-road testing: After install, flex the Jeep and check that the slip joint has enough travel without bottoming out into the transfer case

Frequently Asked Questions

Related Content

• How to Install Adjustable XJ Leaf Spring Shackles — another XJ suspension upgrade from Core 4x4
• Why You Need Control Arms — educational overview of what control arms do and why upgrades matter
• 3 Methods to Rebuild or Repair Your Johnny Joints — maintenance guide for when your joints eventually wear

Shop XJ Cherokee Parts

Fitment: Jeep Cherokee XJ 1984–2001 | Jeep Comanche MJ. Questions? sales@core4x4.com | (385) 375-2104