At Motobilt, one of the most common questions we get from customers who are installing both our Full-Width Axle Conversion Kits and Wheelbase Stretch Kits is:
“What springs should I run with both kits together?”
If you’re building a CJ or YJ with this combo, this article will break down the details so you can set your Jeep up for success the first time around.
Spring Setup: YJ in Front, XJ in Rear
Our front full-width axle kits are designed to use YJ leaf springs, whether you’re working on a CJ or YJ.
The rear stretch kit is designed to use XJ Cherokee leaf springs, which are about 2” longer and have an offset center pin—ideal for wheelbase stretch and suspension geometry.
Match Your Lift Heights
Whatever lift height spring you choose for the front (YJ), match it in the rear (XJ) to maintain proper ride height and balance.
Example:
- 2” lift YJ spring in the front = 2” lift XJ spring in the rear
- Running 4” or 5.5” springs? Match front and rear accordingly.
Mixing different lift heights between the front and rear can cause suspension and ride quality issues.
Pictured:
Jeep YJ full width kit shown with 2.5” lift springs.
Axle and Mounting Notes
Front Kit:
- Moves spring perches outward to accommodate full-width axles and provide more stability
- Fits full-width Chevy/Ford Dana 44 or Dana 60 front axles
*Full width kit does not work with 1980 and newer Ford axles.
Get the Full Width Axle Conversion Kit for YJ:
Without Stinger or With Stinger
Get the Full Width Axle Conversion Kit for CJ:
Without Stinger or With Stinger
Rear Stretch Kit:
- Does not widen the spring mount spacing
- Keeps frame-width spring hangers to retain compatibility with body tubs and bumpers
- Uses XJ leaf springs with a 4.5” offset center pin
- Moves rear axle back ~6 inches without modifying the frame
Get the YJ Wheelbase Stretch Kit
Get the CJ Wheelbase Stretch Kit
Spring-Under vs. Spring-Over Explained
Both kits can be run spring-under (SUA) or spring-over (SOA) depending on your build goals:
Factory Setup (SUA):
- CJ and YJ came from the factory with the springs mounted under the axle
- Running the kit SUA with lifted leaf springs is great for a more traditional, lower-profile setup
Spring-Over Axle (SOA):
- Springs mounted on top of the axle
- Stock YJ/XJ springs moved above the axle net ~5.5”–6” of lift without changing anything else
- Cost-effective way to gain lift—reuse factory springs or grab a junkyard set
Tire Size Recommendations
With the right setup, here’s what you can expect for tire clearance:
| Setup | Estimated Tire Fitment |
|---|---|
| Stock YJ/XJ springs + SOA | ~5.5–6” lift → fits 37–40” tires |
| SOA + 2.5” lift springs | ~8” lift → good for 40”+ tires |
| SOA + Motobilt Highline Fenders + Bump Stops | Can fit up to 42s |
- Highline fenders and comp-cut rear corners give extra room without more suspension lift.
- Running large tires without highlines? SOA + 2.5” lift spring is typically enough clearance.
- Important: For SOA, add a rear anti-wrap bar to prevent axle wrap under load.
Quick Reference: Components & Notes
| Component | Spring Type | Lift Strategy | Notes |
|---|---|---|---|
| Front Axle Kit | YJ leaf springs | SUA or SOA | Perches widened for full-width axles |
| Rear Stretch Kit | XJ leaf springs | SUA or SOA | Stock frame width; axle moves back ~6” |
| Matching Lift | Yes | — | Always match front & rear lift height |
| Spring-Over Lift | — | +5.5–6% | Reuse stock springs; great for 37–40”+ tires |
| Anti-Wrap Bar | — | Recommended | For SOA rear to prevent axle wrap |
Why Pair These Kits?
This combo is a proven setup that:
- Widens your stance for better stability
- Stretches your wheelbase for improved departure angles and better suspension geometry
- Keeps the leaf spring platform simple and trail-proven
Whether you’re building a budget crawler with junkyard springs or dialing in a full custom setup with highlines and 42s—this is one of the most flexible, effective bolt-on/fab setups out there for CJs and YJs.
