Short-Shaft­ing a Trans­fer­Case

How to beef up your driv­e­line

Jp Magazine - - Ta­ble Of Con­tents - By Stu­art A. Bour­don jped­i­tor@jp­ Pho­tog­ra­phy: Stu­art A. Bour­don

Much of the project plan for this 2006 Jeep Wrangler TJ has been to main­tain an old-

school vibe and keep it some­where in the mid­dle be­tween dirt road cruiser and rock­crawler. We wanted a sim­ple and re­li­able build that we can have a lot of fun with. As of this re­port, it sports 4 inches of Cur­rie lift, Cur­rie An­tirocks front and rear, Ran­cho RS9000XL shocks, and 15x8 Mickey Thomp­son wheels. At the mo­ment, a set of 33x10.50R15 BFGoodrich KM2 Mud Ter­rain tires are wrapped around the alu­minum wheels. It can take 35s if we want. All that change cre­ated a chain re­ac­tion, as do most mod­i­fi­ca­tions to any ve­hi­cle. The lift de­manded new drive­shafts, and a slip-yoke elim­i­na­tor kit was needed for the TJ’s New Process 231 trans­fer case to al­low a longer-than-stock rear shaft for bet­ter pin­ion and U-joint an­gles to help elim­i­nate vi­bra­tions.

Af­ter brows­ing for a few hours we set­tled on the Tom Wood’s Cus­tom Drive Shafts Su­per-Duty 231 slip-yoke elim­i­na­tor kit for the NP231 trans­fer case. Why not a low-range gear ra­tio con­ver­sion too? The NP231 of­fers a ver­sa­tile 2.72 low range and di­rect drive in high range. With the 4.0L straight-six engine, six-speed man­ual trans­mis­sion first-gear ra­tio of 4.46:1, and a ringand-pin­ion gear swap that will come with the new lock­ing and lim­ited-slip dif­fer­en­tials (that’s a whole ’nother story to come soon), we can run 33- or 35-inch tires, and the 2006 TJ will have all the gid­dyup it needs to go ex­plor­ing.

What’s the dif­fer­ence be­tween heavy duty and su­per duty? Well, the Tom Wood’s Su­per-Duty 231 con­ver­sion kit comes with the man­u­fac­turer’s unique rear out­put f lange that al­lows the in­stal­la­tion of a 1210, 1310, 1330, and 1350 se­ries drive­shaft with a con­ven­tional two-joint CV (dou­ble-Car­dan) setup, or a 1410 se­ries con­ven­tional two-joint drive­shaft, all with­out chang­ing the flange. As is very com­mon, a Jeep goes through many evo­lu­tions through­out its life­time. Who knows what fur­ther mod­i­fi­ca­tions may be made down the trail. With this setup, we’re not lim­ited to one type or size of drive­shaft, and the flange also of­fers a con­ve­nient spot for a park brake ro­tor if that’s ever in the plan.

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