For hard-core 'wheeling, slower speeds mean greater control and less strain on your drivetrain. However, hard-core 'wheeling also means big tires, which can drain your horsepower and drop your torque curve, leaving your engine sputtering the slower you go.
Swapping in lower (numerically higher) gears into the axles will certainly help you regain some of that lost power and low-speed control, but it may not get you far enough. Also, lower axle gears mean you turn higher rpm on the highway, which can leave your engine spinning a little too fast.
One great answer to this dilemma is changing out the internal gears in your transfer case. This can let you retain good road manners in 1:1 High range and still leave you with the low trail gearing you need - the best of both worlds.
The stock Dana 20 transfer case found in a lot of Jeeps, Scouts, and Broncos is a sturdy and reliable unit. However, its Low-range gear ratio is only 2.03:1. Tera Manufacturing sells a replacement gearset that can convert the stock Low-range ratio to a much more trail-friendly 3.15:1, a gear reduction improvement of 55 percent.
The TeraLow gearset is a complete upgrade kit that includes five replacement gears, thrust washers, an intermediate shaft, needle bearings, and all the necessary seals and gaskets required to complete the installation. The kit is made in two versions for the Dana 20. The Low20 kit uses a six-spline input gear designed for use with factory manual transmissions. The Low20-Auto kit uses a 15-spline input gear for use with the factory automatic transmission.
We ventured to Off Road Unlimited in Mesa, Arizona, to watch the TeraLow kit being installed in a '76 Jeep CJ-7 equipped with a T-18 manual transmission. Robert Brownlee, resident gear guru, showed us the steps involved in tearing down and rebuilding the Dana 20 transfer case.
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Dana 20 ApplicationsFord: '66-'77 BroncoInternational: '65-'72 Scout 800; '71-'79 ScoutJeep: '72-'79 CJ