TeraFlex TeraLow HD NP231 Transfer Case.pdf

Low231 4:1 Heavy-Duty Trans-

fer Case

(LOW231)

Tera Manufacturing, Inc.

5251 South Commerce Dr.

Murray, Utah 84107

Phone/801.288.2585

Fax/801.713.2313

www.teralex.biz

Stop! Read this before beginning installation.

Some YJs and XJs require speciic modiications for proper installation includ-

ing 21-spline applications and shift rail modiications. On TJ models, the

shift rail may need to be trimmed 1/8” in order for the transfer case to be

shifted into 2 High. Please check for proper shifting before reinstalling the

case into the vehicle.

If this product is to be installed on a YJ Wrangler or on a XJ Cherokee, please

contact Tera at (801) 256-9897 for speciic details.

Some older automatics require a transmission seal extension (part #Tl621).

Please check for this part in your kit prior to insatallation. If it is not inlcuded

in kit you can order it from your local distributor or from Tera directly at (801)

288-2585.

Cherokee’s equiped with automatic transmissions take a different Tera

LOW 231 with a different 23 spline input. For Cherokee automatics order

Part #002174300 (old Part#LOW231-23XJA).

High RPM Warning

Do not exceed 2500-3000 RPM for sustained periods of time when using

the Low231 in low range.

Avoid high engine speeds when using the Low231 in low range in 4th or

5th gear with manual transmissions or with high gear automatics. This is

common when driving in snow, mud, or sand. Because the gears are turning

50% faster and with the high gear ratio, it is possible for input speeds to

reach 6500 RPM and cause damage to the transfer case.

We recommend using a lower gear in high-range for higher speeds rather

than running the Low231 at extreme RPM’s.

Before assembly make sure that your

Tera Low231 kit includes:

1- Oil seal (front output)

1- 231 case assembly containing-

Heavy-Duty Case

4.0:1 Planetary assembly

Input shaft bearings

Input shaft and snap rings

Vent itting

1- Automatic Transmission seal

extension (Automatics only)

Break-in Procedure for the Tera Low231

One characteristic of a compound planetary unit, such as the Tera Low231,

is the associated gear noise. Following installation of the Low231, you will

likely hear noise caused by the gear coniguration. This is to be expected of

the new gear system and can be reduced by following some simple break-in

or adjustment guidelines.

Run the vehicle in low-range. A good day on the trail should be suficient

for the gears to quiet down. Running the vehicle in low-range in a parking lot

while accelerating and decelerating will also help quiet the gears.

The planetary gears idle in all positions except low-range. The more low-

range use the gears experience, the quieter they become in all positions.

Revised 9 May 06

Installation Guide for the

231J Overview

The model 231 transfer case is a part-time transfer case

with a built-in low-range reduction gear system. It has

three operating ranges, plus a neutral position. The stock

transfer case provides a ratio of 2.72:1 for increased

low-speed torque capability. The Tera Low231 low-range

system provides a low-range reduction ratio of 4.0:1 for

even more low-speed torque capability.

Disassembly

1. Drain the luid from the transfer case.

2. Remove the front and rear drive shafts.

3. Support the transmission with jack stands.

2. Remove the transfer case from the vehicle. (Refer to

the factory manual if additional assistance is needed

with this step.)

3. Remove the front yoke.

4. Remove the speedometer gear assembly from the

speedometer gear housing.

Operating Ranges

The 231J transfer case has three operating ranges, which

are two-wheel drive high, four-wheel drive high, and four-

wheel drive low. The Tera Low231 changes only the four-

wheel drive low range. Two-wheel drive range is used for

on-road & highway operation. The four-wheel drive ranges

are for off-road operation or when the vehicle is driven on

paved road surfaces covered by snow, ice or similar low

traction elements. The Tera Low231 range is for added low-

speed control in extreme terrain.

Shift Mechanism

Transfer case operating ranges are selected with a loor

mounted shift lever. The shift lever is connected to the

transfer case range lever by an adjustable linkage rod.

Range positions are marked on the shift bezel cover plate.

The shift mechanism is unchanged with the Tera low231.

A synchronizer assembly in the transfer case allows the

unit to be shifted between the two and four wheel high

ranges while the vehicle is in motion. This is also known

as ‘shift on the ly’. Only vehicles with a disconnect front

axle have a synchronizer.

5. On 84-96 XJs and all YJs, remove the three bolts

that connect the tail housing to the speedometer gear

housing. Pry the tail housing off, and remove the snap

ring. Unbolt the speedometer gear housing from the

back half of the transfer case and pry it free.

6. On 97-02 XJs and all TJs, pry the dust shield from the

mainshaft. Remove the snap ring and spacer.

Identiication

A circular ID tag is attached to the rear case of each model

231 transfer case. The ID tag provides the transfer case

model number, assembly number, serial number and low

range ratio. The transfer case serial number also represents

the date of build. For example, a serial number of 6-13-02

would represent June 13, 2002. The Tera Low231 will it

only NP231 (231J) transfer cases. With NP241, 242, 245,

249, and NV247 modiications to the factory case can be

made by arrangement with Tera Manufacturing.

7. Pry the oil seal from the speedometer gear housing,

and remove another snap ring. Unbolt the speedometer

gear housing from the case half and pry it free.

Revised 9 May 06

7. Carefully remove the oil pump. Separate it from the

strainer, be sure that the O-ring stays in the pump

assembly.

10. Remove the mode spring (48).

11. Tap the front output shaft (23) upward with a rubber

mallet to free it from the front output shaft bearing.

12. Remove the front output shaft (23), drive chain (27)

and mainshaft (30) as an assembly.

Note: Remember the order in which the oil pump came off.

A common mistake that is made during re-assembly

is to install the oil pump on the inside of the trans-

fer case. This is incorrect. This will break off the four

mounting tabs on the pump. As the above picture shows

the oil pump is installed on the outside of the case, and

inside the speedometer gear housing.

8. Remove the bolts attaching the rear case to the front

case. Identify the bolts and the washers used at the

dowel bolt locations. These bolts are longer and must

be placed back in the exact location they came from.

9. Separate the rear case from the front case using

screwdrivers. Insert the screwdrivers into the slots cast

in the case ends. Then gently pry upward to break the

sealer bead and separate the case halves. If the two

alignment dowels did not stay in the rear case you

should push them in the rear case at this time.

Caution: Do not pry against the sealing surfaces of the

retainer or rear case. The surfaces could be damaged,

resulting in a leaky case.

13. Remove the mode fork and shift rail (47), and the

synchro sleeve from the front case as an assembly.

14. Slide the range fork pin out of the slot in the sector

(42), remove the range fork (41) and shift hub (13) as

an assembly.

15. Remove the shift detent pin, spring, and plug (20).

Revised 9 May 06

Note: In step 15 if a 3/4” wrench its the plug, you will

need to acquire the new larger detent parts. The fol-

lowing numbers are OEM Jeep part numbers for the

larger pieces.

53008217 Detent pin

53008218 Spring

53008216 Plug

4338956 O-ring

16. Unbolt the range lever from the housing.

17. Slide the shift sector from the case. (42).

18. Remove the sector shaft bushing and O-ring (43) and

save them.

19. Remove the shift indicator switch (4). This may be an

electric switch or a vacuum switch depending on the

year and model of the Jeep. Most Cherokees do not

have a switch in the front case. If you are working on

a Cherokee disregard this step. Make sure the O-ring

seal stays with the switch.

20. Turn the case over and remove the four bolts holding

the front bearing retainer cap together.

21. Remove the front bearing retainer cap (2). Carefully

pry the retainer loose with a screwdriver in the pry

point cast into the retainer.

seals and O-rings prior to installation to prevent dry-

start.

27. Clean the oil strainer carefully. Do not try to clean it

by blowing it out with pressurized air. This will force

particles deeper into the strainer, and will blow holes

in it. Spray it with brake parts cleaner, wiping it occa-

sionally to remove the particles. Repeat this process

until it is free of contaminants.

Reassembly

28. Install new studs using double nuts.

Note: a simple way to install the stud is with double nuts.

Thread two nuts on a stud and tighten them against

each other with a wrench. Repeat procedure for each

stud.

29. Using the new Tera front case half install the front

22. Remove the front output oil seal.

23. Remove the bearing snap ring with a lat head screw-

driver.

24. Tap the bearing out of the case with a plastic mallet.

output shaft bearing, make sure that it is fully seated.

Install the bearing snap ring (21).

30. Install the supplied front output oil seal.

31. Starting from step #22, reverse each procedure back

to step #1. On all sealing surfaces use a 1/8” bead of

silicone sealant to properly seal the surface.

32. Use the torque speciications chart to tighten bolts to

their proper torque rating.

33. When illing the transfer case with oil use DEXRON®III,

or higher grade automatic transmission luid. It is

important that the oil level in the transfer case be

kept up to the ill plug hole. If you have any transfer

case leaks you should ix them before proceeding to

drive the vehicle. If the transfer case is driven with

inadequate oil the planetary gears will be the irst to

seize.

34. Drain and replace the transfer case oil after the irst

one thousand miles, and before three thousand miles.

Inspection/Preparation

Torque Speciications Chart

Components

Torque

25. Now that all of the needed parts have been removed

from the factory transfer case housing, take the new

Heavy-Duty Tera Low231 case housing and prepare for

assembly.

26. Clean all parts that are going to be re-used thor-

oughly. Clean all mating surfaces with brake parts

cleaner. Inspect all parts for wear. Grease all bearings,

Oil pump screws

14 in. Lbs

Yoke nut

110 ft. Lbs

Vacuum switch

20 ft. Lbs

Range lever nut

22 ft. Lbs

Front-case to rear-case bolts

30 ft. Lbs

Rear retainer bolts

18 ft. Lbs

Extension housing bolts

30 ft. Lbs

Drain/ill plugs

35 ft. Lbs

Detent plug

15 ft. lbs

Front bearing retainer bolts

16 ft. Lbs

Revised 9 May 06

Revised 9 May 06

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