LoMax 205 Lowdown: Rebuilding A JB Conversions LoMax 205 T-CasePosted in How To: Transmission Drivetrain on February 28, 2017
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.
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.