J.B. Conversions Inc. NP231 HD w Super Short SYE Reviews, Ratings, Specs & Prices
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J.B. Conversions Inc. NP231 HD w Super Short SYE

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Product Information

MSRP: $1,025.00
Average Price: $460.29
Manufacturer: J.B. Conversions Inc.
Yes: 10 / No: 0

The NP231HD is built with every possible strength upgrade including all that is available through the aftermarket and original equipment manufacturer (NVG). We begin with a bare, empty case and fill it with new components consisting of the following:

Wide chain (genuine Borg-Warner Morse)
Wide-tooth main sprocket and front output shaft
Heavy Duty SYE kit with 32 spline output shaft
6 pinion planetary gear set
Choice of input gear spline (21, 23, 27, 29 or 32 spline)
New bearings, seals, small parts, filter pickup, thrust washers, etc.
No front driveshaft modifications are required: reuse existing front output yoke
The 231HD is a direct, bolt-in replacement for any Dodge or Jeep NP231 transfer case. Bolt patterns and shifting patterns are the same as your original unit. Vacuum actuated front axles are also accommodated.


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Registered User
coconut_pete's Reviews
04-26-2015, 08:08 PM
Price: $299.00
Pros: short. quality made.
Cons: none so far
Recommended? Yes

Comments: the jb conversions website details what makes this sye kit better than the other available super short sye's, so i won't go into all the details other than sending you here: http://www.jbconversions.com/products/sye/np231j_short_sye.php

the only thing i'll detail is the speedo tone ring and sensor. it's way better than the other manufacturers offerings. just be sure to torque it to 200 ft. lbs!


Old Dude
photontraveler's Reviews
12-15-2013, 08:06 AM
Price: $299.00
Pros: tough...............I like the electronic speedo setup
Cons: none yet
Recommended? Yes

Comments: Awesome, well made product............Matched it up with a tom wood driveshaft and could not be happier.


Registered User
robert_hollis's Reviews
01-03-2011, 06:01 PM
Price: $200.00
Pros: super short
Cons: electronic speedo
Recommended? Yes

Comments: I bought mine opened, but new from another JFer, and installed it to go along with my Jeep's tummy tuck (Spring/Summer 2010). it is definitely super short, and it was surprisingly easy to install. I did all the work by myself in a couple of hours out on the road in front of my house. No issues with it, yet. Because it's so short, they had to do away with the gear driven speedo, and replace it with an electronic one. All this means is that I'll have to buy a programmer for my speedo to keep it accurate, if I ever bump up to big tires.

Registered User
onlyn8v's Reviews
09-12-2009, 10:19 PM
Price: $300.00
Pros: Fit and finish is superb, product support is second to none.
Cons: Instructions could use some better illustrations
Recommended? Yes

Comments: This is a expertly designed product. After sale support is insane also. I am really glad I made the decision to purchase this product.


Registered User
Burlbook48's Reviews

01-23-2009, 10:33 PM
J.B. Conversions Inc. NP231 HD w Super Short SYE
Price: $299.00
Recommended? Yes

Comments: Superior product, easy install, but the installation instructions need better pictures. It's a HUGE improvment over the non-SYE, and drivetline vibrations are a thing of the past.

Registered User
brownmice's Reviews

10-06-2008, 01:32 PM
J.B. Conversions Inc. NP231 HD w Super Short SYE
Recommended? Yes

Comments: Excellent product. Instaalled about 2yrs ago and havn't had a problem. Bought the t-case compmlete with sye.Haven't snapped a u-joint yet.Used to snap them every three weeks.


Some Call me RockDog
JeepRocks86's Reviews

09-07-2008, 08:13 AM
J.B. Conversions Inc. NP231 HD w Super Short SYE
Recommended? Yes

Comments: The JB super short kit is very strong and it is top notch in quality.

The only problem is it seems to leak a little bit at the bearing.

It was installed in the spring of 2005


Registered User
zeke6785's Reviews

06-25-2008, 01:32 PM
J.B. Conversions Inc. NP231 HD w Super Short SYE
Recommended? Yes

Comments: Works real smooth and shifts over really nice and the SYE is amazing off road...recomned it

Registered User
jeffmurr's Reviews

05-03-2008, 12:45 PM
J.B. Conversions Inc. NP231 HD w Super Short SYE
Price: $800.00
Recommended? Yes

Comments: Goes into four wheel drive smooth and easy it is strong and steady and works like a tank. it came with the transmission and also came with the original drive shaft.

Registered User
tjthomps's Reviews

03-12-2008, 11:30 PM
J.B. Conversions Inc. NP231 HD w Super Short SYE
Price: $1,025.00
Pros: Part time 4wd and solid design, great folks to work with.
Cons: Shift lever modifications required for WJ no specs provided
Recommended? Yes

Comments: My mechanic installed it, he said it fit just great but for the shift lever modification which we knew, because of research, would require modification and use of the 247 shift lever if we wanted to use the stock shifter, which I did want to do.

Unfortunately, we could not find the specific dimensions for that modification. But, even after all that, we didn't record the dimensions either. So now we know why it was hard to find the dimensions.

We connected it with two Tom Wood's double cardan drive shafts with their 1310 series U-Joints at both the T-Case and Differential. The necessary yokes were purchased from Tom Wood as well. The T-Case came with no front yoke.

We used a 2.5" rear shaft with standard spline (extended life spline was unavailable from Tom Wood in the 2.5" shaft) and a 2" front shaft with extended life spline.

Having "grown up" working for a Fortune 5 company, I have no tolerance for deviation from acceptable customer service. Given that, Both J.B. Conversion and Tom Wood were "good folk" to work with, and Iím not a mechanic.

Iím looking forward to testing this all out.

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