Basically, the outline spline count on an NP231J is 26. But, it’s not a fixed number for all types of transfer cases. Unfortunately, though this spline count significantly impacts a Jeep’s off-road performance, most people just ignore it. As a result, they often fall into several significant issues.
That’s why, as a Jeep owner or driver, you should have a clear idea about the spline count, why this is important, and how much torque and power it can handle. So, continue reading to learn more about this.
What Is the Output Spline Count on an NP231J?
Typically, the term “Spline Count” in a Jeep refers to the number of splines that are present on the axle shaft and a differential side gear that corresponds with the axle shaft.
The number of splines on a Jeep plays a significant role. Because, when you drive a Jeep, it ensures a secure and durable connection between the axle shaft and the differential side gear.
Usually, most of the NP231J’s output spline count is 26. However, the number of output splines on the NP231J transfer case may vary depending on the model and year, with options for 21, 23, and 27 splines.
To determine the correct output splines in your NP231J transfer case, follow these steps:
- Visual Inspection: Remove the transfer case’s drive shaft and count its total spline number.
- Check the Manufacturer’s Specifications: Check your Jeep’s owner’s manual to determine it. But if you lose it, you can contact the manufacturer.
- Use a Spline Counting Tool: These tools are created to count the splines precisely. To count it, just position the device over the output shaft and count it.
Here, to identify which transfer case your Jeep has, check out its TAG. An NP231J has a red and silver sticker on the back of the casing.
They also feature a distinguishing six-bolt front mounting face, so even if the label is absent, you can still recognize them visually.
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NP231J: Model Code Breakdown
The transfer case’s model number includes the manufacturer, the number of speeds/gears, the power, and a number from 1 to 9 designating the kind. If we break down the code, we get the following:
|Code||Meaning of the code|
|NP||Manufacturer Name. Here, NP indicates – New Process Gear|
|2||Two-speed transfer case (Low and High Range)|
|3||Indicates strength level.|
|1||A part-time chain-driven case rather than gear-driven.|
|J||Indicate that this transfer case was created especially for Jeep vehicles.|
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Why Does NP231J Output Spline Count Matter?
An NP231J transfer case is a significant element of several four-wheel drive vehicles, especially Jeeps.
And its spline count significantly impacts a Jeep’s driving characteristics and overall performance. Here are 3 reasons in detail why this spline counts matters:
Reason 1: Understanding Its Ability to Handle More Torque
Generally speaking, a higher spline count indicates that the transfer case can tolerate more torque without risking the possibility of the spline teeth falling apart.
It could impact the longevity and strength of the transfer case because additional splines spread the torque load across a larger surface area.
That’s why this spline count is crucial for Jeep fans who like modifying their cars for off-road driving or heavy-duty hauling.
Reason 2: To Ensure Compatibility with Other Drivetrain Components
Spline count also matters when it comes to ensuring compatibility with other drivetrain components.
Because incorrect spline counts may cause poor fit, more deterioration on the drivetrain’s parts, and even failure.
For example, if your transfer case has 21 or 23 splines, your drive shaft and yoke must also have 21 or 23 splines.
Reason 3: It Impacts Overall Vehicle Performance
Another reason this is important is that it could impact how smoothly power is transmitted to the wheels.
Here, the number of splines can impact the final drive ratio (a measure of how many teeth are on the ring gear and how many are on the pinion gear in the differential).
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How Much Power and Torque Can an NP231J Handle?
The NP231J can handle up to about 300 to 350 HP in typical applications. And in regular use, an OEM 231 transfer case can deliver torque ranging from 1600 to 1900 ft. lbs. (This number is far larger than NVG claims).
Moreover, the 241’s six-pinion gear set has a torque rating of 1,400 lb-ft, and the 231’s three-pinion gear set has a torque rating of 600 lb-ft.
But, if you want more strength, upgrade it with wider chains, larger planetaries, and stronger mainshaft/tailhousing modules.
These modifications typically help a transfer case handle more than 2900 ft-lbs of torque. But only exceptional engineering and refining can make this possible.
Nevertheless, you might not always receive this output since the NP231J transfer case’s capacity to control power and torque is dependent on several variables. Here are those variables:
- Overall weight of the vehicle
- Driving manner
- Tire dimensions
- Use case
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Is the NP231J a Good Transfer Case?
The NP231J is a well-liked transfer case that is widely utilized in four-wheel-drive vehicles like Jeeps, Dodges, and Chryslers.
It’s a chain-driven, part-time transfer case with high and low ranges.
Speciality of NP231J
- It’s a New Process Gear transfer case’s family member.
- This is well-regarded as a strong transfer case.
- It maintains a good balance between dependability and performance.
- This transfer case sends power to the vehicle’s front and back wheels, which enhances your Jeep’s grip and stability in off-road situations.
- Its casing is made primarily of aluminum, which makes it lightweight in comparison to other transfer cases.
- Because of its simplicity and low maintenance cost, it’s a favorite option among off-road adventurers.
- It has two ranges. One is: Low-range gear with a decent 2.72-to-1 ratio. And the other is: Direct-drive high range.
Unfortunately, like any mechanical issue, the NP231J is also prone to breakdowns or deterioration over time.
But, you can increase the longevity of any transfer case by performing routine maintenance and using it properly.
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After reading this article, it’s probable that you still have unanswered questions. We tried our best to address the most frequent queries. Read this FAQ to find the details you need.
What fluid goes in a 231J transfer case?
The NP231J transfer case needs automatic transmission fluid (ATF) or a compatible transfer case fluid that complies with the Mopar MS-9224 standard. However, a lot of people like to use a pure 30 weight oil or a 5W30 synthetic or mineral oil.
What is the low-range gear ratio on an NP231J?
An NP231J transfer case’s low-range gear ratio is 2.72:1. This entails that the output shaft spins at a rate of 2.72 rotations for every rotation of the input shaft. This ensures more torque but lower speed limits.
Are all 231J transfer cases the same?
No, not every NP231 transfer case is identical. From 1983 until 2001, NP231 had a total of nine variations. They are, MP231, NP231A, NP231F, NP231G, NP231B,NP231D, NP231E, NP231C, and NP231H.
What is the fluid capacity of an NP231J transfer case?
When an NP231J transfer case is entirely drained and refilled, it requires more than 2 quarts (or 1.89271 liters) of fluid. For optimum performance, it is necessary to use the right fluid type and quantity.
What is the cost of replacing the NP231J transfer case?
Repairing or rebuilding an NP231J transfer case typically costs between $500 and $1,000, including labor costs. But, considering other aspects, such as the vehicle type, location, and labor prices, this price range might change.
Unfortunately, the NP231J transfer case has some limitations. Such as, driving over rough surfaces like asphalt or concrete, might result in premature chain breakdown in this unit.
So, while driving, drive carefully. Also, if you bought a used Jeep, double-check the tire diameters.
Because it’s possible that used car sellers mismatched the tires to sell the vehicle, which will result in the NP231J transfer case failing.
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