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NP241 Home Remedies: JB Conversions Helps Make A Transfer Case Better Than New

Posted in How To: Transmission Drivetrain on August 10, 2017
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The New Process 241 is an aluminum-case, chain-drive transfer case that was used in Chevy, Dodge, and Jeep 4WDs beginning in 1987. It was offered with both passenger- and driver-side front outputs, with input spline counts from 23 to 32. Low range ratio is 2.72:1 using a six-pinion planetary assembly. Versions were built for mechanical speedometer cables and for electronic vehicle speed sensors.

The NP241 is a solid, reliable transfer case and superior to the NP203 it replaced. But as they age, the drivechain can stretch. Also, the synthetic pads on the shift forks wear, causing intermittent problems when the forks do not stay in their intended position. Lastly, unchecked rear seal leakage can lead to eventual lubrication starvation and failure.

We needed an NP241 for a project we’re working on. They’re quite plentiful so we easily sourced one from a ’95 Chevy Silverado at a salvage yard for a mere $135. However, one big downside to this case is the rear driveshaft slip-yoke at the rear. The housing is long at the tail and the rear yoke seal is prone to leaking. This setup with the slip in the transfer case is also less reliable than when the slip occurs in the driveshaft itself.

JB Conversions offers a number of proven slip-yoke eliminator (SYE) kits to solve this problem on the NP241 and other transfer cases. JB Conversions’ John White says, “We were the first to come out with the HD 231 SYE and 241 SYE with a 32 spline shaft in 1993.” We opted to use the company’s Standard Length SYE kit to both shorten the tail of our transfer case and improve reliability. JB Conversions also offers the hard to find master rebuild kit for our T-case, so while we had much of the case torn apart we decided to restore its operation with new wear components. One-stop shopping!

We were able to complete the entire process on a workbench in less than a day using mostly common mechanic tools, but did use a press to install a couple of bearings. We’ll show you a good overview here of the JB Conversions SYE kit installation, plus what it takes to rebuild the NP241. But, there are more details. One resource we’ve found to be useful is the NP231/241 Guide from Automatic Transmission Service Group (ATSG). It contains full disassembly and assembly procedures for the transfer case, along with detailed information on its operation.

Here’s our donor transfer case with the long rear slip-yoke housing. The slip-yoke adds extra length to the transfer case (less length to your driveshaft) and is prone to leaking over time.
We began the teardown by removing the front yoke. To remove the bolt we held the yoke in place with a bar we bolted on. Some mechanics will hammer these yokes off and on with an impact gun, but it’s difficult to properly torque the nut with that method.
After removing the rear extension and retainer housings, the rear case was separated from the front case to reveal the chain and gears.
The multi-link chain was pulled from the case along with the front output shaft.
The next major disassembly was removal of the shift mode fork along with the mainshaft assembly. Then the range fork assembly and the shift sector were pulled.
Here you can see the six-pinion planetary, low-range assembly. Its mating ring gear remains behind in the front case half. Other than removing a few bearings and seals from the housings, this completed disassembly and we moved forward to cleaning all the parts and inspecting everything.
We began the reassembly and rebuild using a master rebuild kit from JB Conversions. A new front bearing was tapped into the front case assembly. We used automatic transmission fluid for lubrication during assembly.
There’s a pilot needle bearing inside the input gear. An appropriate driver is helpful for installing the new one with a press fit, but we were able to do the job with some scrap steel stock we had on hand.
The low-range assembly was taken apart and inspected. The input gear and the planetary gears looked fine. We found a good deal of black debris in the bottom of our transfer case upon disassembly and were not sure what the origin was until this point. The culprit was that the old thrust washers were cracked with portions completely missing. We cleaned everything up and reassembled with fresh thrust washers.
The low-range assembly was slipped back into the bearing in the front case. The manual cautions about pushing excessively on this assembly for reinstallation. However, ours dropped in from above with the help of gravity and a gentle tap.
Snap rings are used on a number of the bearings and shafts. A good pair of flat bill retaining ring pliers is extremely handy for dealing with each of them. Here, the input gear was secured in the front case with a snap ring, then followed with the bearing retainer cover with a new seal.
The shift sector received a new O-ring and bushing where the shaft exits the case to mate to the shift lever. The high-low range fork engages in the slot and the mode fork is actuated by the bumps along the edge where the thumb is resting. There is also a shift detent pin (bottom of case) used with the shift sector.
Here’s the new JB Conversions mainshaft mating with the large drivechain sprocket and synchronizer assembly. The synchronizer is what allows the transfer case to be shifted between 2-Hi and 4-Hi ranges while the vehicle is in motion. The splined and threaded end is where the new SYE output yoke will reside.
An NP241 will start to develop issues with the shift fork engagement and stability as the synthetic fork pads wear. These were all replaced using new pads supplied in the JB Conversions rebuild kit.
The shift forks, mainshaft assembly, front output shaft and a new BorgWarner drivechain were all worked into place in the front case.
A magnet at the bottom of the case helps catch steel particles that are shed as parts wear. Upon opening the case, we found lots of small chunks from the broken thrust washers, but minimal metal debris.
This caged needle bearing fits in a blind hole in the rear case. A blind hole bearing puller would have been handy to get the old one out, but we didn't have one on hand. Some careful work with a Dremel cutting disc allowed us to score the cage and then peel the bearing out. We used a shop press to install the new one.
The NP241 uses a shaft-driven pump to pick up fluid from the bottom of the case and route it to the top to lubricate the internal parts. We installed a new seal in the pump and a new oil pickup screen.
While guiding the oil pump in place on the mainshaft, the rear cover was installed. We used silicone RTV sealer on all the case surfaces. Bolt torque values were found in the ATSG guide.
On the tail of the mainshaft is either a speedometer drive gear or a reluctor ring (as shown here) for an electronic speed sensor. Snap rings are used to hold this piece in position.
The Standard Length JB kit reuses the factory rear retainer. We installed a new bearing from the kit and then bolted the JB aluminum bearing retainer in place. The rear retainer and the yokes were the final items installed during the build.
Here's the completed slip-yoke eliminator setup ready to mate to a traditional 1310 CV driveshaft. JB offers several output yoke options and several kit types for the NP241, including the company’s Shorty kit that further reduces the overall length of the transfer case.

Sources

JB Conversions
Sulphur, LA 70664
337-625-2379
www.jbconversions.com
Automatic Transmission Service Group
800-245-7722
atsg.us

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