Re-Gearing the TJ — 4.56, 4.88, and 5.13 Ratios

The TJ's 4.0L inline-six makes its best torque between 2,000–3,500 RPM. Stock gear ratios (3.07 on 1997–2001 Dana 35 base models, 3.73 on most others) produce acceptable highway performance with 30" tires because they keep the engine in that band at 65–70 mph. Put 35" tires on a 3.73-geared TJ and you've effectively reduced the mechanical advantage by roughly 14%, which means the engine now has to rev higher to do the same work, low-range crawl ratio suffers, and the transmission is hunting for a lower gear on every hill. The 4.0L will tolerate it, but it will never feel right.

Gear ratio selection follows the tire diameter. For 35" tires, 4.56 is the widely-used street/trail ratio — highway manners are restored and the crawl ratio improves significantly. For 35" tires on a dedicated trail build, or for 37" tires on any build, 4.88 is the better answer: more low-end authority for rock work and acceptable highway performance with the overdrive working harder. The 5.13 ratio is for highly modified rigs running 37"–40" tires with aggressive gearing strategies — it's not a street ratio and carries a real fuel economy penalty.

Front and rear gears must match exactly. The TJ uses independent axle housings front and rear, and if you install different gear ratios in each axle, the transfer case will transfer torque between them every time 4WD is engaged, creating binding in the drivetrain. The common mistake is gearing one axle at a time for budget reasons — the result is a rig you can't use 4WD on safely until both axles match. Do both axles at the same time or be prepared to drive the first axle in 2WD-only until the second axle is geared.

Budget for professional installation if you don't have differential experience. Ring and pinion installation requires setting bearing preload with an inch-pound torque wrench, measuring backlash with a dial indicator, and reading gear tooth contact patterns with marking compound. A misset pinion depth or incorrect preload will destroy the gears within 5,000–10,000 miles.

Steps

1. Drain both front and rear differentials completely.
2. Remove axle shafts from the axle to be geared (front requires removing the front driveshaft and disconnecting the front axle shafts; rear requires removing rear axle shafts).
3. Remove the differential carrier from the housing.
4. Remove the ring gear from the carrier; install new ring gear with new ring gear bolts. Torque ring gear bolts to 70–80 ft-lbs in a crossing pattern.
5. Press old pinion bearing races out of the axle housing; press new races in.
6. Install new pinion with correct shim stack for target depth (requires pinion depth gauge — measure, shim, check, repeat).
7. Set pinion bearing preload using crush sleeve or shim pack per manufacturer spec (rotating torque: 15–25 in-lbs on new bearings).
8. Install carrier with new side bearing shims; set backlash to 0.006"–0.009" (Dana 30) or 0.005"–0.008" (Chrysler 8.25").
9. Check tooth contact pattern with gear marking compound — pattern should be centered on the drive face of each tooth.
10. Install new diff cover gasket or RTV; torque cover bolts to 25 ft-lbs.
11. Refill with correct gear oil: 80W-90 synthetic (Dana 30), 80W-140 synthetic (Chrysler 8.25").
12. Repeat for second axle.
13. Drive 500 miles before re-checking fluid for metal particles indicating break-in wear.

Why it works

• Restores highway drivability and proper low-end torque after moving to 35" tires
• 4.88 gears with 35s produce a crawl ratio (with the NP231 4:1 low range) of approximately 87:1 — genuinely capable for rock work
• Matched front/rear gear sets are required for safe 4WD operation — this upgrade is non-negotiable for 35" tire builds
• Yukon and Nitro gear sets are widely available with documented fitment for TJ axles
• Improves fuel economy compared to stock gears + oversized tires by returning the engine to its efficient RPM range

Trade-offs

• Installation requires differential expertise and specialized tools — incorrect installation damages gears within miles
• Both axles must be geared simultaneously or 4WD cannot be used safely
• Full cost including labor at a shop runs $1,500–$2,200 for both axles
• Gear break-in requires 500 miles of varied driving before hard off-road use
• Chrysler 8.25" limited-slip owners must verify the locker/LSD choice is compatible with the new gear set's side bearing spec

Tools required

• floor jack
• jack stands
• torque wrench
• pinion depth gauge
• dial indicator
• bearing press
• INCH-lb torque wrench
• socket set
• RTV sealant
• gear marking compound

Parts

Sources

• JeepForum — TJ Re-Gear Guide: Choosing the Right Ratio
• Yukon Gear — Ring and Pinion Installation Instructions
• 4WheelDrive Hardware — TJ Gear Ratio Calculator

Related

• Rear Locker for the TJ — Chrysler 8.25", Dana 35, and Dana 44
• Running 35" Tires on the TJ — Lift and Fitment Requirements
• Long-Arm Lift System — 4.5"+ for Rock Crawling ($2,000+)
• All Jeep Wrangler TJ guides & tools
• Browse the full DIY database

Written and maintained by an AZ wheeler and driveway wrencher. How we source guides. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.