NP231 HD Std. Length SYE - New Housing (Applications Below)

HD Super Short SYE


Part #16-1200-1942 -- $249.00 (w/1310 CV Yoke)

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Part #16-1200-1983 -- $255.00 (w/1310 Non CV Yoke)

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Part #16-1200-1946 -- $255.00 (w/1350 Non CV Yoke)

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Part #16-1200-1966 -- $284.00 (w/1350 Rear Output Flange)

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  • Use with Jeep NP231J transfer cases in TJ, YJ, and XJ vehicles
  • Compatible with GM NP231C & NP233C transfer cases requiring Chrysler type speedometer pickup
  • Compatible with Dodge NP231 requiring Chrysler type speedometer pickup


The Heavy Duty yoke kit includes a new output shaft with superior design qualities:

  • 18% Larger spline diameter.
  • 32 splines on the output end of the shaft as opposed to the original 27.
  • The larger diameter output shaft gains a 54% increase in torque capacity over the original.
  • Factory heat treat retained.
  • No resplining, annealing, weld overlay, or cutting done to the new output shaft.


  • The new 1310 CV end yoke supplied in the kit has been redesigned from the more common Spicer 2-4-5341 yoke (shown for the Advance Adapters, Inc. SYE kit - below photo).
  • Our new yoke has additional clearance for those of us needing a high angle driveshaft. The new JB Conversions, Inc. yoke is also shorter than the competition. Internal spline length within the JB Conversions, Inc. yoke is held equal to the Spicer yoke at 2.00".

Yoke Comparison

JB High Clearance CV Yoke


Yoke Comparison

JBC vs Spicer (and others)


The 32 spline HD SYE kit has become standard issue to anyone utilizing a NP231 transfer case in a lifted Jeep. An abundance of look-a-like SYE kits are now on the market. Our company provided the original HD SYE in 1994 and continues to provide exceptional SYE kits for Jeeps, Blazers, and fullsize pickups. The popularity of the Jeep SYE kit has allowed for increased quantities and lower raw materials pricing from the gear shops and casting manufacturers. The resulting volume pricing has allowed us to offer the standard HD SYE kit for a low price. The kit ships complete with the same components as packaged since 1994.

Every year model of the NP231 can be accommodated with the standard HD SYE kit. Variations in speed sensors, cables, etc. can be factored into the packaging of the kit so that your kit works perfectly every time. This kit is also available in a pre-built NP231HD with beefed up internals and all new parts.

If your SYE kit needs surpass the benefits of our proven standard length SYE, check out our new "SHORTY HD SYE" kit.


The model NP231 transfer case is a compact, chain-driven transfer case manufactured by New Venture Gear (New Process Gear) in Syracuse, New York. Since the early 80's, the model 231 has been used in many vehicles and is designated as follows: NP231C = GM S-10, S-15 trucks & Blazers 1983 - 1991, NP231D = Dodge midsize and fullsize trucks, NP231J = Jeep YJ's, TJ's, and some XJ's. This transfer case was first introduced in Jeep Wranglers in 1988 after replacing a 1-year run of NP207 transfer cases.

All "J" models of the NP231 are not created the same. There are internal differences among different year models and this kit has been designed to be compatible with each version. Our fixed yoke kit has been installed in hundreds of V8 equipped Wranglers (small block and big block) to date without a single shaft failure. Because of this success, the new output shaft carries a lifetime replacement warranty.

Why should you buy the JB Conversions kit instead of any other?

In addition to the technical aspects discussed below, several design and manufacturing specifications set this kit apart from the competition. The JB kit includes a new U.S. made shaft that is manufactured following direct specifications from NVG drawings down to every detail (heat treat spec.'s, material spec., hardness, spline data, etc.). JB Conversions does NOT use a shaft that is manufactured to a "copy" spec. of an original New Venture Gear shaft.

The rear bearing housing supplied in our kit is a custom one-piece design that is molded and machined to exact specifications. Dimensional data for the speedometer gear bore, bearing bores, base flange spec.s, etc. have also been set to perfectly match New Venture Gear engineering data. After all machining processes have been completed, each housing is sent through a pressurized, high temp. liquid vat to seal the aluminum pores against any possibility of leakage (a procedure not done by the competition). The new housing is also cast with an internal oil gallery which operates as a drain port to keep oil flowing across the output bearing. This internal port also reduces the chances of seal leaks caused by the build-up of pressure between the bearing and oil seal. For years, New Venture Gear, Inc. has utilized a dual spring, dual lip oil seal on many of their transfer case front output yokes. We have chosen to follow their lead and install a premium seal of this type in every new housing.

There are 3 main reasons to install the Heavy Duty Slip Yoke Eliminator kit in your Jeep:

1) Strength:

With the exception of the stock output shaft found in the "J" model, the NP231 can handle considerable abuse without exhibiting any signs of distress. The planetary gear assembly, drive sprockets, and chain in the 231 are very strong and rarely have problems. When there is a problem, low oil level is usually the cause of failure. The original 27 spline output shaft in the 231 is the only real weak point in the entire unit. The stock output shaft features a spiral cut speedometer gear just past the rear output bearing. The minor diameter of the speedometer gear teeth is fairly small. When the shaft fails it will almost always break in this area.

2) Lubrication:

The rear output "slip-yoke" design of the NP231 is notorious for leaking. The rear driveshaft yoke used with a slip-yoke style transfer case is designed to slide back and forth across the splines of the output shaft. Under normal driving conditions and vehicle payload, the slip yoke will remain within a narrow range of movement across the splines and seal surface. The surface area past this narrow margin is exposed to the elements and will form a ruff surface due to rust and dirt. Once the vehicle becomes loaded down with trail gear, or the suspension is cycled heavily, the slip yoke will travel even more therefore dragging the corroded surface across the rubber output seal. This is where the leaks start. Over time, a low oil level could be reached within the transfer case and the result could be catastrophic failure.

Another problem with the slip yoke design is that the rear driveshaft yoke cannot be removed from the vehicle without loss of transfer case fluid. Broken u-joints can often require the vehicle to be driven back to civilization on the front shaft only. Without a fixed yoke on the rear output, this task would be impossible without experiencing major transfer case damage due to loss of oil.

Kit Upgrade: The HD slip yoke kit utilizes a standard Dana Spicer end yoke. This "bolt-on" yoke eliminates the leak prone slip yoke entirely. With the addition of the fixed yoke, the rear output seal runs in one location on the yoke therefore seal life is maximized.

3) Driveline angles:

On any short wheel base vehicle, driveline angle is critical and easily influenced with the addition of a suspension lift. Typically, Jeep Wranglers come factory equipped with a rear driveshaft that is 13.5" or less. With a running length this short, every inch of added suspension lift has a drastic effect on the angle of the driveline.

Kit Upgrade: The only way to DECREASE the working angle of the U-joint is to lengthen the driveshaft. Once installed, the HD yoke kit will add 4.5" (YJ's) to 6.5" (TJ's) of length to the rear driveline therefore flattening the overall slope of the shaft.

Gains in driveshaft length are based on measurements taken from the center-of-u-joint on the original driveshaft to the front of the case. Be careful in buying a slip-yoke kit based on the claimed length "number" in inches. It is better to look at the design of the new rear housing in the fixed yoke kit as opposed to that of the rear housing of the stock tcase. Remember this; the stock NP231 has an output bearing at the rear of the speedo housing as does the new slip-yoke eliminator kit. These bearings are within 0.25" of the same location as measured from the front of the case. The shortest design for a yoke kit would be to place the yoke immediately after the rear bearing. The JB kit does exactly that. Anything shorter would require a shorter end yoke or more shallow rear housing and that is not possible due to the size of the speedometer gear bore. What this means is that the JB kit is designed to be the shortest overall length possible regardless of where you measure from.

After the installation of the JB kit, the improved operating angles of the u-joints will greatly increase the life of the driveline. The new HD yoke kit is shipped with a C.V. compatible end yoke and requires a 1310 series u-joint. Other end yokes are available to accommodate larger u-joints however the 1310 is the preferred joint.

Additional Info

Installation Instructions

Install Instructions

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