Dana 300 4:1 Tera Low Installation

Glenn’s 85 CJ-7 has little problems off road. One issue is a crawl ratio that is somewhat high (32.3:1) The T-176 transmission has a 3.52 low gear and Glenn’s Jeep has 3.54 axle ratios. The Dana 300 transfer case offers a 2.62:1 low range which makes Glenn’s Jeep tolerable off road but it could stand some improvement. A transmission or axle ratio change would be costly and time consuming.

TeraFlex offers a low range kit for Dana 300’s that increases the low range ratio to 4:1. The kit consists of 5 gears that replace all of the transfer case’s original gears. This modification requires some grinding to fit the idler gear into the case.

After completion this small change will improve the Jeep’s ratio to 49.8:1 from 32.3:1 while still maintaining good cruise rpm and street drive-ability. Follow along as this project progresses.

This table is a comparison of crawl ratio between the TeraLow and stock gearing. The Jeep is equipped with 3.54 axle ratios. The formula is gear X transfer case X axle ratio = crawl ratio.

Trans Gear 2.62:1 Gears 4:1 Gears
1-3.52 32.6 49.8
2-2.27 21.1 32.1
3-1.46 13.5 20.6
4-1.00 9.2 14.1
R-3.52 32.6 49.8

You can see the improvement on 1st gear. Also 2nd gear is almost the same as the original 1st, this will come in handy when not in an absolute crawl situation.

There are several models of the TeraLow, there are TeraLow’s for Dana 300 (4:1), Dana 20 (3.15:1), Dana 18 (3.15:1), and NP 231 (4:1). Check out the TeraFlex web site for more detail.

TeraLow Kit

Dana 300 Rebuild Kit

Now onto the project.

Stage 1 – Buy Stuff and Extra Transfer Case

Glenn picked up the TeraLow from OK Auto and ordered a rebuild kit for the transfer case. We also picked up a used Dana 300 to do the gear swap, this way the Jeep is left intact until ready for installation.


Stage 2 – Disassembly of the 300 and “Gentleman…start your grinders”

Continue to Part 2