Tera Low for the Dana 300 Transfercase
It doesn't seem that long ago when the only
way to lower your crawl ratio was by installing lower gears in the differentials.
The only problem is, the reduction of highway speed. You really had to
be sure of your choice once going beyond gearing correction for tire size.
Over the last few years several manufacturers have come out with crawler
gears for transfercase's. The advantage being, you can install lower "low
range" gears while leaving you 1:1 high range for the highway. Tera Manufacturing
is one of the leaders in these low range conversions with kits for the
Dana 20, Dana 300 and 231 transfercase's found in early Jeeps, Broncos,
and the current YJ-TJ. What you get from the 300 T-case is a reduction
in low range from 2.62:1 to 4:1 giving you a 50% increase in crawl ratio.
What is your Crawl ratio and how to calculate? It is simply the combination
of you 1st gear + differential gearing + low range in the transfercase.
In the case of a 304 equipped Jeep (as is our case) 1st gear 3.52:1x diff
gearing 3.07:1x transfercase 2.62:1= 28:1. With the Tera kit your low
range goes to 42:1 and your second gear low range ends up 28:1! This gives
you two low gear choices for crawling instead of one. The same 42:1 can
be achieved through gearing the differentials but 4.56:1 gears would be
needed to reach the same low range (I know that is what I currently run.
The problem is highway speed is drastically effected, leaving a comfortable
cruising speed of about 90 kilometers an hour. Not great for the 401 through
Toronto!
The Tera-Low for the Dana 300 T-case is installed exactly the same as rebuilding with stock equipment but for a small grind needed inside the case for the larger diameter main gear. Ordering the bearing kit will get you a complete rebuild with all necessary parts. Finding a reputable shop in your area may be your main task as the kit needs a professional installer, though with some prior knowledge it could be installed in your own garage. Install time at Dumont Tirecraft (preformed by Wayne Foster after hours) took about 5 hours. This should be about right for any professional, baring problems. The instructions are straightforward and easy to follow. Like the 231 case, installed in the 95 YJ last issue, the trail differences were apparent right from the start. The ability to have more gear choices and to leave the damn clutch alone makes for less wear on the drive-train and driver. Price one out for your own truck, it may be a better choice than super low gears in the differentials, (and probably about the same price installed) especially for a daily driver.
Details...
 1. The Tera case on the
right is nearly identical to the original but uses a 5 planetary gear
system. The original Tera kits came with a three planetary gear system
that was found inadequate with the added torque of the lower gear
ratios. |
 2. The stock gears slide
out easily in their proper order. If you have never taken a transfercase
apart this is a job best suited for a professional. The install took
a total of 5 hours from teardown to completion. |
|||
 3. |
 4. |
|||
 5. We ordered the optional
install kit. The first case lasted for 20 years so with new bearings
we hope to get another 20 from the new set up. |
 6. This is what you get. The three gears on the right are the reduction gears and the two on the left are direct replacements for your stock side gears. And the shift rod is designed to make space for the larges main gear assembly. The first Tera kits only came with the reduction gears but after finding the stock gears were not strong enough to handle the extra torque of the reduced gearing they opted to make the kit with the side gears as well. |
|||
 7. |
 8. The Tera gear is on the left with the stock gear on the right. |
|||
 9. |
 10. A small amount of grinding
is the only modification needed inside the stock case. As the main
gear is so much larger than the stock one the notch is needed when
sliding the main gear into place. |
|||
 11. |
 12. The roller bearings
are installed one at a time into the main gear. A set goes into each
side with a spacer in the middle. |
|||
 13. One of the shift rods
is replaced with the Tera rod. As the main gear is a larger diameter
a notch is needed to clear the gears. This is not optional, if you
do not use the Tera rod you will not be able to install the gears
|
 14. The main gear is the
last to be installed and as you can see by the tight fit that the
small notch that was needed in the case was necessary. |
|||
 15. Here the completed
t-case is ready to be reinstalled |
 16. |
|||
|
||||
