2006 Jeep Wrangler Gear Swap

Whether you're looking for a beefier manual transmission or are one of those weirdos who likes the transmission to do the shifting for you, here are some worthy transmission-swapcontenders.

1. GM Turbo 400
Highs: Incredibly strong, works well at angles, and is adaptable to nearly any engine and T-case.
Lows: Stock First gear is only 2.48:1, takes about 30 hp to spin, and at 24 1/2-inches long, it's a tight squeeze in a short-wheelbase rig.
For you if: You want a brutally strong automatic that works well off-road and have the room to swing it.

2. NV3550
Highs: Lightweight, 4.01:1 First gear and 0.78:1 Fifth gear, has same 23-spline output shaft as most modern-day Jeep T-cases, smooth shifting, and strong aftermarket support for swapping.
Lows: Not up for big power over 300 hp and 350 lb-ft of torque, noisy Reverse-idler shaft at idle, 24-inch long case is somewhat long for short wheelbases.
For you if: You've got at least 85-90 inches of wheelbase and don't run huge tires or tons of power.

3. NV4500
Highs: Stands up to big-block or diesel power, excellent 5.61:1 First gear and 0.73:1 Fifth gear, strong aftermarket support for swapping.
Lows: Incredibly heavy at about 195 pounds dry, overall length of 25-26 inches prevents installation in short-wheelbase vehicles, and physically deep so it will hang down unless drivetrain is raised.
For you if: You want the jack of all trades in a manual transmission - brutal off-road strength, killer low gearing, and highway-friendly overdrive.
4. World-Class T-5Highs: Surprisingly stout behind engines up to about 300 hp and tires smaller than 35s, quick bang shifting possible, and lightweight.
Lows: Can succumb to hard rockcrawling and heavy strain with big tires, not as much aftermarket support as with many other 4x4 transmissions, and useable cores becoming slightly hard to find.

For you if: You want a quick, dragstrip-like shift for the sand or prerunning.

5. SM420
Highs: Best First gear out there at 7.05:1, very short case at 10 1/2 inches, the small-block Chevy of the transmission world.
Lows: Not found in junkyard as easily as once was, balky shifting characteristics, and no overdrive.
For you if: Short wheelbase and big strengths are your thing.

6. GM Turbo 700R4
Highs: Velvety-smooth shifting, very good 3.06:1 First and 0.69:1 Fourth gear, and very strong aftermarket support.
Lows: Long case length of 23 3/8 makes it hard to squeeze in Wrangler or short-wheelbase chassis, requires big cooler to prevent overheating, and needs upgrades to survive with larger tires or more than 350 hp.

For you if: You want to drop your Jeep in gear on the trail and forget about it, then cruise home with the tach at 2,100 rpm.

7. Torque Flight 727
Highs: Arguably as strong or stronger than the TH400, bolts to many Jeep engines (including the 4.0L and ZJ 5.2L and 5.9L engines), and short 16-inch case length fits several chassis.
Lows: Meager 2.45:1 First gear, not as many shifter options as GM transmissions, four-wheel drive versions becoming rare.
For you if: You want to keep your Jeep drivetrain Mopar and need the strongest auto you can get.

8. NV5600
Highs: Incredibly overkill, 5.63:1 First and 0.73:1 Fifth coupled with tight gear spread through other four gears mean plenty of pulling power, laughs at up to 650 lb-ft of torque.
Lows: Incredibly heavy at just over 360 pounds, long wheelbases only, bellhousing is part of front of tranny and requires a special adapter (available through Dynatrac) and complete transmission disassembly to mate to different engine. Also, big 1 3/8-inch, 10-spline input shaft requires 12 1/4- or 13-inch clutch and big 1 1/2, 29-spline output shaft would be difficult to mate to Jeep T-cases.
For you if: You've got the bucks to make it happen and just want the bragging rights of having the biggest, baddest manual out there.

9. NP435
Highs: Huge strength with a relatively light 135-pound package, excellent 6.68:1 First gear, and relatively easy to adapt the Ford version to non-Ford engines or the Dodge version to Chrysler and some Jeep engines.

Lows: Slightly easier to find in junkyards than SM420 but still somewhat elusive, balky bread-truck shift characteristics.

For you if: Your Jeep didn't come from the factory with a T-18 or T-98.

10. Powerglide
Highs: Can be built to handle stupid amounts of power (over 1,200 hp), extremely lightweight, very short case length for either two-wheel or four-wheel drive applications.

Lows: Aftermarket parts to build it up are pretty expensive, only a two-speed transmission, and stock cases are pretty much worthless if power levels or big tires climb into stratosphere.

For you if: You've got a really lightweight rock Jeep or hit the dunes with a lot of power.