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JB Conversions LoMax 4:1 Gears
for the Dana 300

By Jack Brinks

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The Dana 300 transfer case is one part of many Jeeps that rarely gets swapped out, mainly because of its strong cast iron case and decent low range gear ratio of 2.62:1. It also can be rotated to improve ground clearance, and its only weakness, depending on how hard you wheel, is the rear output shaft, which can be upgraded with several available aftermarket kits. I used a transfer case rotation kit and a heavy duty, 32 spline output shaft kit from Advance Adapters to upgrade these areas.
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T he only other upgrade a rockcrawler could want for the Dana 300 would be lower gears. The options at this point have been limited, but, with the introduction of LoMax gears from JB Conversions, the playing field has been expanded immensely! One look at these new gears will bring new meaning to the phrase “a picture is worth 1,000 words.” Look at the size of those gear teeth!

Comparing them to stock Dana gears, there is no mistaking the quality of the machining and obvious strength of the LoMax gear set. JB Conversions spared no expense in creating these gears, using state-of-the-art machining processes to create them out of solid steel alloy. LoMax gears were designed from day one to be a complete 5 gear set. This allowed designing the biggest, strongest gear teeth possible. Most, if not all, competitors use 2-piece press fit and welded gears. This is a much less expensive process, adequate for stock vehicles, but is no way near as strong as LoMax gears. JB Conversions assures us these are the largest gears you can put in a Dana 300 - bar none. They say that because of the design and manufacturing processes used, the LoMax gears are “far superior to any other gears being produced for the Dana 300.” Looking at the gears, I see absolutely no reason to dispute this claim!

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OK, enough of stating the obvious. Let’s get on to the install. After I got over gawking at the gears, I checked out the rest of the kit. JB Conversions includes high quality, double-lipped seals for optimum sealing, heavier shift detent springs, and new shift rails modified for gear clearance. The heavier detent springs are included because twin stick applications sometimes have the tendency to “pop out of gear,” disengaging either the front or rear axle. Mine does this at times (or did, hopefully), especially when descending a steep hill under load.

Also included are some of the best, most comprehensive instructions I’ve ever seen. About the only thing they didn’t cover is removing and installing the transfer-case, but if you don’t know how to do that, you probably shouldn’t be attempting this anyway! These instructions can be previewed on the JB Conversions website, at www.jbconversions.com/pdf/lomax.pdf. If you’re not sure, read the install instructions first before you decide to go on.

JB Conversions LoMax
Where to grind
You’ll need several special tools, along with normal hand tools, including a press, gear puller, dial indicator, external snap ring pliers, and a grinder. If you are still not comfortable, consider having a pro do the install for you. Also, depending on the condition of your transfer case, you may want to consider purchasing an overhaul kit at this time, since you’ll have the whole case apart anyway.

Do to the variations in Dana 300 measurements, the instructions run you through a pre-assembly check of several gear clearance measurements. It’s very doubtful that you’ll have any trouble, but do it anyway. Also, after disassembly, you will need to grind a small notch in the case to allow installation of the larger idler gear.

The photo to the right indicates where to remove the material from the case.

Start by removing both output yokes and the inspection cover. You’ll need a 1 1/8” socket and maybe a puller for the yokes, but most likely you can tap them off with a small hammer without the puller.

Next, remove the retainer for the cross shaft and tap it out with a brass drift or a large wood dowel. Make sure you recover all needle bearings and the 3 retaining rings from inside the idler gear. If you are not using an overhaul kit, you’ll need to reuse the needle bearings.

JB Conversions LoMax

Next, remove the 2 shift fork set screws, using a 3/16” Allen socket. Don’t try this with a regular Allen wrench. Go buy a good one. Then, remove the 2 pressed-in detent plugs in the front bearing housing by driving a pick through them and prying them out. Also remove the shift indicator switch and threaded plug.

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Remove both shift rails, using a punch or Phillips screwdriver to rotate them as you pull them from the case. Be very careful not to lose the detent balls, springs, or shift interlock pills.

Now you can remove both shift forks from the case - smaller one first. Next is the input bearing retainer. Use a small mallet or rubber hammer to get it started and then use 2 pry bars to remove it.

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Remove the speedo gear from the rear output housing, noting its orientation in the housing for re-installation, and, using a puller or carefully tapping with a mallet or small hammer, remove the output housing. Be sure to retain the shims located behind the rear bearing.

JB Conversions LoMax

Next is the front output rear bearing retainer plate and shims along with the front output bearing retainer. Use a rubber hammer and pry bar to remove the latter.

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Use a puller to remove front output helical gear and tapered roller bearing. Then remove the sliding gear. Position the transfer case carefully in a press and remove the front output shaft from the gear and bearing. Again, position the case carefully and use the press to remove the rear output shaft from the remaining gear and bearing.

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Disassemble the input gear assembly by removing the retaining ring. You’ll need a good pair of external snap ring pliers for this. Then use the press to push the input gear out of the bearing. The seal may be pushed out, as well, but it’s going to be replaced. Be certain to retain the shims between input gear and bearing.

JB Conversions LoMax

The last step of disassembly is grinding the notch in the case to allow installation of the larger LoMax idler gear. If you remove too much material, the only problem would be sealing the inspection cover properly. Just use the photo and take your time. When done, wash the case thoroughly, removing all metal case and grinding wheels particles. I use grease-cutting dish-washing liquid, like Dawn, to help in this process and flush with hot water. Dry everything completely. Now, we’re ready to put it back together!

JB Conversions LoMax





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