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.
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!
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!
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
If you’re not sure, read the install instructions first
before you decide to go on.
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.
Where to grind
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.
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
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.
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.
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.
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.
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.
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.
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!
TO THE INSTALLATION --->>>