Re-gear from 4.10 to 4.56 for 37s on Power Wagon

The 2014-and-later Power Wagon comes from the factory with 4.10:1 gears in the front AAM 9.25" axle and rear AAM 11.5" axle, behind the 6.4L HEMI. (The 2005-2013 truck paired the 5.7L HEMI with 4.56 gears and an AAM 10.5" rear — this guide's ratios apply to the 4.10 trucks.) With factory 33" tires, that gives a comfortable crawl ratio and acceptable highway RPM. Bump tires up to 37" and:

• Effective ratio drops from 4.10 to ~3.61 (multiply factory gear by 33/37)
• Throttle response gets sluggish, most noticeably at altitude and under load
• Transmission hunts for gears, dragging MPG and shift quality
• Low-range crawl ratio drops from 73:1 to ~64:1 — noticeable on technical climbs

Re-gearing to 4.56:1 restores the 33"-tire feel with 37s. The math: 4.56 / 4.10 = 1.112x, which exactly offsets the 37/33 = 1.121x tire growth. Within 1% — you can't tell the difference from factory.

For the 6.4 HEMI (2014+, factory 4.10): 4.30 is acceptable, 4.56 is better. The 6.4's torque masks some of the lost gearing, but for sustained high-altitude crawling or towing, 4.56 is the right call.

For the 5.7 HEMI (2005-2013, factory 4.56): you already have 4.56s. Going to 37s on that truck means 4.88s to restore the factory feel, and the older AAM 10.5" rear limits ratio availability more than the 11.5" does — confirm the ring and pinion is offered for your axle before planning the job.

Cost breakdown:

• Front + rear ring & pinion sets: $740 (Yukon or similar)
• Master install kit (bearings, races, shims, seals, marking compound): $580
• Shop labor (both diffs): $1,200 — most owners pay; this is not a DIY job for the average wrenching skill level
• Total: ~$2,500 done

DIY considerations: Setting up a ring and pinion correctly requires:

• A case spreader or shop press for carrier bearings
• A dial indicator for backlash measurement (0.005-0.008" target on AAM)
• Marking compound for tooth-contact pattern verification
• Pinion-depth shim experimentation (3-5 attempts is normal)
• Patience — first-time installers should expect to disassemble and re-shim 2-3 times

If you've never set up a ring and pinion before, the AAM 11.5" rear is NOT a good first-time job. Pay a shop. The $1,200 labor saves a $740 ring & pinion that you'd otherwise scrap from a bad install.

Even if you pay for it, knowing the sequence tells you whether the shop is doing it right and where your money goes.

1. Both diffs come apart. The AAM 9.25 solid front and the AAM 11.5 rear are pulled down, old ring & pinion and carrier bearings removed. The factory locker carrier is reused — you are changing gears, not the locking hardware.
2. Pinion depth is set first. The installer presses on a pinion bearing, installs a starting shim, and reads the tooth-contact pattern with marking compound. This is the step that takes time; 3-5 shim iterations is normal even for a pro.
3. Backlash is dialed in. Carrier shims move the ring gear until backlash measures 0.005-0.008" on the AAM, verified with a dial indicator. Pattern and backlash get cross-checked until both are in spec.
4. Pinion preload is set with the crush sleeve (or solid spacer), then the whole thing is buttoned up with new seals.
5. The other axle gets the identical ratio. Front and rear MUST match — a 4.56 rear behind a 4.10 front binds the driveline in 4WD and destroys parts.
6. Speedometer is corrected afterward, either at the dealer or with a tuner cable (~$150), or your odometer and shift logic stay off.

If you have set up a ring & pinion before, the 11.5 rear is doable; if you have not, this is the wrong axle to learn on — see the parts list and the pw-tires-mt tire decision that drives the whole choice.

The single most expensive mistake is mismatched ratios front to rear — it feels fine in 2WD and then binds and grinds the moment you engage 4WD on dry pavement, and by then the damage is done. Verify both axles got the same gear before the truck leaves the shop. The second is a rushed pattern: a contact pattern that is close but not centered will whine at cruise and wear early, so do not accept "good enough" on the marking-compound check. For a DIY attempt, the realistic failure is scrapping a $740 gear set on a bad first install — which is exactly why the $1,200 labor is cheap insurance for most owners.

Why it works

• Restores factory drivability with 37" tires
• Improves MPG by 1-2 (counter-intuitive but true — engine works less hard at cruise)
• Required for proper transmission shift logic on any 37" build
• Re-uses the factory locker hardware (no other axle changes needed)

Trade-offs

• $2,000-2,500 done at a shop
• Both diffs must be re-geared together (mismatched ratios = drivetrain bind in 4WD)
• DIY is a steep learning curve; failed first attempts are common
• Adds ~150 RPM at 65 mph cruise — slight highway noise increase
• Speedometer correction needed (or use a tuner like a HP Tuners cable, $150)

Tools required

• bearing puller
• case spreader (or shop press)
• dial indicator
• torque wrench (250 lb-ft)
• shop press for carrier bearings
• patience

Parts

Sources

• Yukon Gear & Axle — AAM 11.5 and 9.25 ring & pinion applications
• American Axle (AAM) — 9.25 solid front / 11.5 rear axle service specifications
• Power Wagon Registry — re-gear and tire-size discussion threads

Related

• Mud-Terrain Tires for Power Wagon (KM3 / Patagonia M/T / Open Country M/T)
• Locker Upgrade Path for Power Wagon (Factory + Tru-Lok or ARB Bulletproofing)
• All Ram Power Wagon 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.