Before you can install a long arm kit on a Jeep JK Wrangler, you have to tear the old suspension apart, drop the gas tank, and cut every factory control arm bracket off the frame. It is the most intimidating part of the build — and also the most straightforward if you have the right tools and take your time.
In this video, Spence from Core 4x4 walks through the complete tear down and prep on the shop JK — a dedicated 100% off-road rig running 40-inch tires and Currie 70 axles. This is Part 1 of a two-part series. Part 2 covers the full long arm kit install with bracket welding, arm measuring, and torque specs.
Fitment: 2007–2018 Jeep Wrangler JK / JKU (2-door and 4-door)
The Build: Core 4x4 JK Long Arm Kit
The kit going on this Jeep is the Core 4x4 long arm kit for the 2007–2018 Wrangler JK. It works on both two-door and four-door models and is a true four-link system — long upper and long lower arms on both axles. Core 4x4 does not use the radius-style or long-lower-short-upper designs that cause axle wrap and limit suspension cycling at lifted heights above 4 to 4.5 inches.
This is a full weld-on kit, which means the factory brackets must be completely removed from the frame. That requires a sawzall, grinder, and some patience. The reward is a clean, purpose-built suspension platform.
Step 1: Remove All Control Arms
With the Jeep on the lift, the first step is pulling every control arm — front upper, front lower, rear upper, and rear lower on both sides. Support the axles on jack stands so they are not hanging solely on the shocks.
This JK was already running Core 4x4 Crawl Series control arms and track bars (front and rear), so the old arms came off easily. If your Jeep has factory arms with seized bolts, budget extra time and plenty of penetrating fluid.
Step 2: Drain and Drop the Gas Tank
The rear long arm brackets require welding between the gas tank and the frame. The tank has to come out — there is no way around it. On the JK, the gas tank is held up by a skid plate rather than straps, so the process is a bit different from older Jeeps.
Siphoning the fuel
Spence siphoned the fuel the old-fashioned way — disconnect the filler hose at the top of the tank and use gravity with a rubber hose. He went through four gas cans on a full tank. There is a check valve in the fuel system, so go in at the filler hose connection rather than trying to siphon through the filler neck itself.
Easier method: Disconnect the fuel line at the fuel rail, trip the relay for the fuel pump, and let the pump push the fuel out into your cans. Faster and cleaner — but Spence was already committed to the manual approach.
Dropping the skid and tank
The JK gas tank skid doubles as the only thing holding the tank up. Remove the transmission skid first (four bolts), then start on the tank skid bolts along both sides. Leave the front two and rear two bolts in until you have a transmission jack or floor jack supporting the weight.
There are four connections at the rear of the tank (filler hose, evap line, and two fuel lines) and two at the front. Use fuel line disconnect tools — the cheap Harbor Freight set works, but higher quality tools are less likely to break the brittle plastic clips.
Safety note: Make sure all fuel is cleaned up and the studio or garage is fully aired out before you start cutting or grinding. Fuel vapor and sparks are a bad combination.
Step 3: Tools for Cutting Brackets
This is the part that intimidates most people, but with the right tools it is straightforward. Here is what Spence used:
- Sawzall (reciprocating saw) — does the bulk of the work, gets tight to the frame and makes clean cuts. Use quality blades — Diablo medium metal blades are thinner and flex into tight angles
- Angle grinder with cut-off wheel — find a wheel with a recessed mount so the grinder sits flush against the frame. This prevents gouging the frame rail
- Flap discs — small ones for detail cleanup, larger ones on a bigger grinder for final smoothing of cut welds
- Batteries — if you are running cordless (Milwaukee, DeWalt, etc.), have every battery you own charged. This is a lot of cutting. Or just use corded tools
Consumables used on this tear down
| Item | Quantity Used |
|---|---|
| Sawzall blades (Diablo medium metal) | 12 |
| Cut-off wheels | 3 |
| Small flap discs | 3 |
| Large flap discs | 2 |
A 15-pack of sawzall blades would have been enough. If you are faster or more efficient with a sawzall than Spence, let him know in the comments.
Step 4: Cut the Front Brackets
The front lower control arm mounts are fully welded to the frame. Cut through the welds with the sawzall, working from both sides of the bracket. Use the grinder to clean up anything the sawzall cannot reach, then finish with a flap disc to smooth the frame rail.
Take your time here. You are cutting welds, not cutting the frame. If you go too deep, you will gouge the frame rail. Let the tool do the work and do not force it.
Step 5: Cut the Rear Brackets and Body Mount
The rear is more involved than the front. You need to remove:
- Lower rear control arm mount (passenger side requires the gas tank to be out for access)
- Upper rear control arm mount
- Factory body mount — the new long arm bracket replaces it entirely
Start by unbolting the body mount, then cut the welds on the bracket assembly. On the rear passenger side, the welds are between the frame and where the gas tank sits — this is exactly why the tank has to come out.
Despite the extra brackets, Spence found the rear easier to access than the front. The grinder could get into the welds more easily, and the brackets pried off without as much fight.
The Result: Clean Frame Ready for Long Arms
With all four brackets removed and the frame cleaned up, the JK is ready for the next phase — fitting and welding the new long arm brackets, measuring and setting the arms, and reassembling everything.
Spence estimates about two hours of actual cutting time if you are experienced with a sawzall and grinder. Add time for battery changes, blade swaps, and the inevitable pause to figure out why a particular weld will not let go. Plan a full day for the complete tear down including the gas tank.
What Comes Next (Part 2)
Part 2 of this series covers the full long arm install:
- Fitting and welding the new front and rear brackets to the frame
- Weld-through primer and box welding for corrosion protection
- Measuring and setting control arm lengths
- Torque specs for all fasteners
- Pinion angle check and adjustment
- A surprise color change on the arms to match the Jeep
Why a True Four-Link Long Arm Kit?
Core 4x4 builds their JK long arm kit as a true four-link — long upper and long lower arms on both axles — rather than the common long-lower-short-upper design. Here is why that matters:
- No axle wrap: Equal-length uppers and lowers keep the pinion angle stable under acceleration and braking
- Better flex: Long uppers swing through a wider arc, giving the axle more room to articulate on uneven terrain
- Smoother ride: The four-link geometry works like it is supposed to — each arm controls one aspect of axle movement without fighting the others
- Less stress on components: Short uppers with long lowers create a lever arm that hammers bushings, joints, and brackets. A balanced four-link distributes forces evenly
Above 4 to 4.5 inches of lift, a long arm kit is where you start gaining real benefits over short arms. Below that, upgraded short arms are usually sufficient.
Frequently Asked Questions
Tools Required for Tear Down & Prep
- Lift or jack stands (support both axles independently)
- Basic socket set and wrenches
- Reciprocating saw (sawzall) with metal cutting blades (15-pack recommended)
- Angle grinder with cut-off wheels and flap discs
- Larger angle grinder with big flap disc (for final frame cleanup)
- Transmission jack or floor jack (for gas tank)
- Fuel line disconnect tools
- Gas cans (four for a full tank)
- Rubber hose for siphoning (or use the fuel pump relay method)
- Penetrating fluid
- Safety glasses, gloves, hearing protection
- Fire extinguisher (mandatory when cutting near fuel system areas)
Related Content
- Core 4x4 JK Wrangler Long Arm Kit — the kit used in this install
- JK Long Arm Install Pt. 2 (Full Install) — bracket welding, arm setup, torque specs, and final assembly
- Why You Need Control Arms — educational overview of what control arms do and why upgrades matter
Shop JK Wrangler Parts
Fitment: 2007–2018 Jeep Wrangler JK / JKU (2-door and 4-door). Questions? sales@core4x4.com | (385) 375-2104
