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LoMax 205 Lowdown: Rebuilding A JB Conversions LoMax 205 T-Case

Posted in How To: Transmission Drivetrain on February 28, 2017
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There is little debate or doubt that gear-driven transfer cases have been a popular swap for hardcore wheeling rigs, and often they have been the choice for builders over chain-driven designs for good reason. Of the gear-driven options, the NP205 has been one of the most commonly used cases for serious off-road enthusiasts and builders for multiple reasons, including their sheer strength; the ability to add doublers to cure the inferior, factory 1.96 low range ratio; and there’s twin-stick options and plenty of aftermarket support when it comes to finding bearings and seals for repairs or rebuilds. It’s a time-tested case that has proven to be one that can take a beating out on the trail and still hold up through time and, occasionally, neglect.

Our JB Conversions LoMax 205 had begun emitting a growling noise and vibration that was getting progressively worse. Our 205 is fine while under load, has an ORD twin-stick on it that functions properly, and is without issue until we are on the coast-side or remove the load. At that point, the demon within comes to life leaving us to wonder: Will we make it one more mile or will we hear the dreaded “bang” that off-roaders hate and fear most? We figured that instead of waiting until it craters on the trail, it would be smarter to take a proactive approach, get inside, see what’s going on, and fix the problem.

If you are unfamiliar with JB Conversions’ LoMax 205, here is some info that will give you a better understanding of the science behind it. The case itself is machined to the same tolerances as the original NP205, but it’s made from a ductile or nodular iron casting. The LoMax design has additional ribbing inside, thicker walls adding even more strength to the case, while the nodular iron offers a unique combination of strength, wear and fatigue resistance to the finished product. JB Conversions kept the case dimensions identical to the original NP205 design to eliminate modifications to drivelines, shifters or mounting for those replacing a stock unit. One of the biggest advantages of the LoMax is the wider, stronger 3:1 ratio gearset that replaces the inadequate 1.96:1 ratio that a stock NP205 comes with, making it a worthy swap for any build intended for the trails.

During the transfer case removal process, we found a couple of things that could possibly be contributing factors to what we were experiencing as far as the noise and vibration. The transmission adapter had come loose from the crossmember and the front U-joint on the rear driveshaft had seen its last mile. All things considered, we knew we still wanted to get inside the T-case to see if there was anything that could potentially become a bigger problem down the road.

Before we started tearing this case apart we wanted to knock the accumlated grime off of it so we tossed it into the parts washer for a quick degreasing. Starting with the parts in a clean condition helps identify any issues that may be hidden under built up grime.

After getting the case removed from our Jeep we headed down to Inland Truck Parts in Casper, Wyoming. Inland Truck Parts has years of experience with 205s, and Shop Foreman Chris Cochran was more than eager to help us tear into this project and figure out what, if anything, was causing this case to sound so horrible. As we pulled each gearset out and began to inspect them, we were pleasantly surprised, yet somewhat puzzled, to see that not only did the components appear to be fully intact, they were in excellent condition. The bearings and races as well as the gears all looked like they were freshly installed, giving a sense of confidence that this case was functioning and holding up incredibly well. About the only thing that remotely stood out as the possible culprit and cause of the noise was a very slight appearance of engagement and wearing of the inner teeth on the inside of the slider rings. We completed the rebuild using standard off-the-shelf NP205 parts. After a short amount of deliberation, we also decided to replace our Jeep’s driveshafts since the others had seen years of abuse. We reached out to our friends at J.E. Reel Driveline, and the team built us some new ’shafts to finish off the project.

After the rebuild, it was time for a shakedown run. With equal amounts of anticipation and reservation, we loaded up figuring the only way to find out if it worked was to put the Jeep on the road. To our relief, almost all of the noise and vibration was eliminated. As we know with our types of crawlers, they will never be long distance comfort cruisers and since our rig is built for the rocks we’re feeling pretty good about being able to comfortably run 40 mph while heading back and forth to the trails. Even though nothing stood out within our 205 as being the sole issue, rebuilding it definitely tightened things and was worthwhile since it had seen a decade of hard wheeling and was in need of some attention.

Here are some of the highlights of our LoMax 205 rebuild.

Here’s the fully assembled unit before we began removing the twin-stick setup, shift rail linkage, spud shaft, transmission adapter, and front output flange.
With the front bearing retainer and rear output shaft/gear assembly removed, we simply had to tap the front output shaft towards the rear of the case so we could fully remove and inspect it.
Here, Cochran is preparing to remove the idler shaft from the case before the final step of removing the intermediate gear and shift rails along with the shift forks, leaving the case completely empty and ready for one more cleaning before we began reassembling our LoMax 205 with the new components.
The case is disassembled and ready for one last trip through the parts washer while we set out the new bearings and seals for the reassembly.
Here, the components are spread out for a final inspection before the new bearings, races and seals are pressed in or into the drive assemblies.
It is always recommended that when something of this magnitude is disassembled, new races, bearings, seals and gaskets are used when reassembling the unit. These components are among the lowest cost items in a transfer case and are the most common to failure.
For those who might want or need the help of a good set of step-by-step instructions, JB Conversions has an online PDF that can be downloaded and printed so you have a reference guide on-hand during the rebuild process.
With the new seals in place, the rails and forks were installed, all of which had to go together in a specific order to allow the poppet balls to properly engage with the detent notches on the shift rails. Once the forks were properly positioned on the shift rails, we locked them in place with the roll pins.
The input bearing was installed and an external snap ring was installed on the input shaft, which also helped hold the shaft in place while we installed the slider ring into the fork inside the case before installing the output shaft.
Next, the needle bearings were installed and the rear output shaft was installed onto the rear of the input shaft. The rear output bearing housing was then bolted down after applying a thin layer of RTV sealant and gasket. Once the bearing housing was tightened down the tailhousing was installed using the same method and torque specs.
With the input and output shafts installed, we applied a thin bead of RTV sealant and gasket before mounting the Advanced Adapters transmission adapter.
The front output roller bearings and gear assembly were installed into the case followed by the rear bearing retainer and front bearing housing and flange. All mounting surfaces received a layer of RTV and a gasket or new seals.
We installed the shift linkage before the flange, allowing us a little extra room to work.
The poppet balls, springs and caps were reinstalled into the case so they could perform their task in conjunction with the shift rails.
Before any of the bolts were reinstalled they all got a dab of thread locker to ensure we don’t have any issues of bolts backing out while out wheeling.
Lastly, the inspection cover was reinstalled and sealed with the same RTV sealant and gasket as on the rest of our other mounting surfaces.
With the rebuild finished and ready to install into the vehicle, we have complete confidence we should not be experiencing any issue from our transfer case.
We’re ready to get back out on the trails and have some fun!


JB Conversions
Sulphur, LA 70664
JE Reel Driveline Specialists
Inland Truck Parts

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