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November 2011 Techline

Amsoil Gear Oil
Willie Worthy | Writer
Posted November 1, 2011

Your Tech Questions Answered

Gear Lube or ATF for NP205?
I’ve always been told to run 80W-90 gear oil in my transfer case (NP205), but recently I’ve had my transfer case rebuilt, and when I went to drain it and put some fluids in it, tranny fluid came out. It seemed to be the same Dextron 3 I run in my transmission, so I called around and got people who were sure it was tranny fluid and people who were sure it was gear oil, but I wanted to ask some fellow four wheelers who know from trial and error.

Which should I run: transmission fluid, or 80W-90 gear oil? It is the original transfer case on my ’72 Chevy . . . yeah, it’s old.
Chim Chim
Via fourwheeler.com

The NP205 and NP200 take just what you have been told to use—75W-90 gear lube, about 4.5 pints. The same goes for any of the Dana-series cases like the 18, 20, and 300. The NP203 with its chain drive, however, is designed to use 10W-40 engine oil, and I always recommend using a synthetic lube.

For those of you wondering about other transfer cases, most all of the New Process/New Venture cases take ATF. Here again, I recommend a synthetic lube. Rebuilders tell me a better lube is 5W-30 engine oil, and that is what I use.

Oh, and you may find some factory reference to using 50-weight engine oil in the NP205 as well as the Bronco version of the Dana 20. I’ve have even had people tell me that all Dana transfer cases can run 50W engine oil. In reality, it has about the same viscosity as a 90W gear lube with a different additive package.

Wants Ranger Torsion Key Lift
I was looking at a torsion key leveling kit for my ’06 Ranger 4x4 Sport. I want bigger tires, but I don’t know what the ride would be like afterwards. Rangers are kind of rocky from stock (side to side). Has anyone done this to their Ranger? I was thinking of 32x10.50 BFG tires.
06ranger4x4
Via fourwheeler.com

Yes, the torsion bar key leveling system will work on your Ford Ranger. You’re thinking right by using a 32x10.50-size tire. Put it on an 8-inch-wide rim that has 4.5 inches of backspacing. ReadyLift has what you will need (www.readylift.com).

As to ride quality, well, it will suffer due to limited downward wheel travel. To control the “rocky” ride, I suggest a gas-pressure shock like a Bilstein 5100 or perhaps some adjustable shocks like the Pro Comp MX-6 or the Rancho RS9000.

Death Wobble Mystery Solved Forever! Or Not
In the Mar. ’11 Techline, Lou Keller of Cuyahoga Falls, Ohio, asks for help with a “death wobble.” This event is more common than is realized. Mechanics have been chasing this problem with altered vehicles for a long time, and spend lots of the customer’s money experimenting to see if they can solve the issue, often leading to less wobble but seldom to no wobble. The problem always shows itself after a lift kit is installed. Sometimes, changing the tire size or pressure will reduce the problem, but not entirely solve it. Toe-in is not the problem—this will cause premature tire wear and wandering, not wobble. Camber will not cause it, though it does have some effect due to the changing of tire size that usually accompanies the lift. Changing tire size changes the point at which the line between the upper and lower ball joints intersects the pavement in the tread pattern unless careful attention is given to the offset of the wheels to keep the line where the factory designed it to be.

Out-of-balance tires and wheels do not cause it. Worn-out parts do not cause it—you can drive a vehicle with worn-out unitized hubs, worn-out ball joints, worn-out steering linkage, the wrong camber and improper toe-in, and all that will happen is poor steering control and premature failure of tires.

The root cause of “death wobble” is always related to the caster angle of the front axle. Too much or too little can cause it, and the speed at which it occurs upon hitting a bump in the road is determined by the amount it is off. Remember the days (if you are old like me) of extreme choppers with very long rake angles? They often experienced the same problem. Even a shopping basket at the grocery store will experience some degree of wobble after the front wheel has been hit enough to change the angle of the caster. Trucks with lifts are notorious for having this problem because we like to lift them to make room for bigger tires.

Not all lift kits are created equal. Not all manufacturers put the time into engineering the proper caster into the kit. Many simply design the kit for lift and clearance without thorough testing with different wheels and tires. It is often assumed that the factory specs are good enough, but that is sometimes not the case. Caster has a limited range in which it works; again, too much or too little, and you have problems. Yes, it is important to have everything else correct as well for the safety of all involved, but it is caster that is the root cause of the problem. Find the correct caster angle for the combination of lift, wheel width, and tire diameter, and the problem will go away. Been there, done that many times. Hope this helps. I’ve been reading queries like this for years in many magazines, and the expert always takes a shotgun approach to the problem when surgical-precision rifle shots are what are needed.
Gary McClenny
Irving, TX

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