Skip to Header
Skip to Navigation
Skip to Main Content
Skip to Footer
Toggle navigation
Home
About Us
Customer Rigs
My Account
Contact Us
home
Toggle navigation
Search
Search
My Account
|
Sign In
(0) in cart
Toggle navigation
Custom Steering
Leaf Spring Products
Drivetrain
Lighting
Recovery
Custom Suspension Links
Builder Parts
Tabs and Brackets
FST Merchandise
Cherokee (XJ)
Key Chains
Signs
Toyota
Beadlocks
Dodge
Home
Drivetrain
NP231 Doubler Adapter
Zoom in on Image(s)
Included but not in the picture is the short shaft and all needed hardware
Thumbnail
Thumbnail
Thumbnail
Thumbnail
Thumbnail
Add to Wish List
Add to Gift Registry
Email a friend
Share
|
NP231 Doubler Adapter
5/5 rating
1
Review(s)
1
5
5/5 rating
1
5
Write a Review
Your Price:
$485.00
NP231 Doubler crawl box adapter with clocking ring for your Jeep Wrangler TJ,YJ, or Cherokee XJ
Part Number:
FS-NP-231
Availability:
1 Week Lead Time
Choose Options
Rear Case
*
231J
Dana 300
23 Spline SHAFT ONLY (-$185.00)
231 Aluminum Adapter plates ONLY (-$185.00)
Rear Case Spline Count
23 Spline
Put me on the Waiting List
Quantity
+
-
Add to Cart
Submit
product tabs
Description
Customer Reviews
Need lower gearing on the trail while still being able to cruise on the highway? FST now offers our 231 Doubler Adapter with rear case clocking ring. This adapter turns the front planetary half of the 231 you have laying in the shop into a 2.72:1 crawl box. This kit can be bolted to the back of the front half of existing 231J 21 or 23 spline transfercases. Then you can choose which round 6 bolt rear case to run. There are many options so do your research or ask questions if needed. The most commonly used rear case is a 23 spline 231J, a 231J with 231C or HD 6 gear planetary, and even a 23 spline Dana 300. With our clocking ring you can rotate the rear case in 7 degree intervals to provide more clearance or a transfer case flip.
Our doubler kit comes complete with the adapter plate and clocking ring manufactured from 6061 1/2" aluminum, the weld in block off plate already pre ground to a perfect fit and ready to weld in, a new custom splined 4340 chromoly heat treated half shaft, and all the needed hardware.
Here is a great assembly video. A couple main difference is we now offer sight-glass plugs with our kits and there is now a counterbore to hold the shift rod secure in the adapter.
https://youtu.be/F26f22_Cab8
To complete your doubler install you will need to source your own 231J front half and a complete 6 round bolt pattern case to run in the rear. You will also need driveshafts made for your required length. An additional crossmember to support the rear case is always a great idea.
Rating Snapshot
Select a row below to filter reviews.
5 Stars
1
4 Stars
0
3 Stars
0
2 Stars
0
1 Stars
0
4 Stars
Clear Filter
?
Average Customer Ratings
5.0
5/5 rating
Collision tech. And fabricator
Great quality! And received order on time! Verry pleased??
Did you find this helpful?
1 of 1
Found Helpful
Reviewed by:
Troy Russell
from Colorado on 5/20/2026
5
5
Related Items
SIMPLE T Case Shift Linkage
$40.00
In Stock. Ready to Ship.
Add to Wish List
Select Options
242 Frame Side Shift Lever
$30.00
In Stock. Ready to Ship.
Add to Wish List
Add To Cart
T Case Shift Lever
$15.00
Back Order
Add to Wish List
Add To Cart
47RH, 47RE, 48RE 2nd Gear Lockup Plate
$25.00
In Stock
Add to Wish List
Select Options
Doubler Adapters
$500.00
1 Week Lead Time
Add to Wish List
Select Options
category breadcrumbs
Browse Similar Items
Cherokee (XJ)
>
Drivetrain
Recently Viewed Items
Turn History Off
×
0
Items
Menu Links
Categories
