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January 2008 4x4 Tech Questions - Techline

Willie Worthy | Writer
Posted January 1, 2006

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Question: I am in the process of swapping a pair of '79 Dana 60 axles into my '79 Bronco. With 9 inches of lift, I need to correct the pinion angles. I bought Dedenbear Cs to correct the front, and heavy-duty spring perches for out back.

What is the maximum pinion angle I can run on each axle before starving the pinion bearings? I've been told 18 degrees is the number, but have heard 12 and 25 degrees also. With everything mocked up, with Cage radius arms and the pinion pointing straight at the double cardan (plus or minus a degree), it's at 19 degrees.

I was also told of a modification that can be made to a washer of some sort involving some well-placed cuts and bending it to act like an impeller. Have you heard of this and know if it works?

Also what's your opinion on relocating the fill hole to add more fluid?
Chris Howland
Lebanon, CT

Answer: This is a really good question. I always figured, or read some place, that about 8 degrees was maximum. Maybe it was from a conversation with a Spicer engineer where he mentioned it. Then again, this can vary with the design of the rear end. So out of real curiosity I made some inquiries: Chris at Code 4x4 (970/625-8998, ) has custom-built a lot of rear ends and says that he has gone as much as 20 degrees, even on street-driven vehicles, without a problem, but he doesn't recommend going that high. Terry at Randy's Ring & Pinion (866/246-4897, says 15 degrees is the maximum. Steve at Dynatrac (714/596-4461, says 9 degrees is the maximum. However, Dynatrac also offers on its rear end, or through selected dealers only, a special option of what the company calls "dual high-sump oiling system." There is some custom work involved when installing this kit, and it is not for the do-it-yourselfer. With the kit installed (by one of their dealers), they say it can work up to 18 degrees, and they've even heard of some going as high as 24 degrees.

Some people recommend using a big flat thin washer, sometimes referred to as a "slinger," between the pinion gear and the bearing to sort of act like a dam and hold the oil in the bearing. I believe it was originally designed to prevent too much oil from going forward and overloading the pinion seal. Maybe I am wrong. Some Dana 60s have them, while others do not. Just keep in mind that it will act as a shim and definitely affect the pinion depth setting. I tried to find some information on making the slinger into an impeller without much luck.

Now, keep in mind that there is a big difference between a trailer queen that only sees limited highway use and a street-driven rig. When off the highway, the ups and downs move the oil around and usually lube things quite well. Going down the highway at speed, it could be quite easy to starve the pinion bearings of oil.

All three of those folks I talked to (as well as myself), agree that you definitely need to overfill the housing. How much? Tough question to answer. Most likely to the point where oil doesn't start coming out the vent tube when driving down the highway at speed. Probably the easiest way to do this is back the vehicle up a very steep ramp, or to jack the rear of the vehicle up to the point where the pinion is nearly level. Then fill the rear end up to the fill plug. Some vehicles with high-pinion housings have differential covers with a much higher fill plug, while several aftermarket covers have the fill plug in a higher location.

The subject of synthetic lubes-versus-non-synthetics is a very debatable question, with several builders of custom housings saying that the synthetics don't offer enough resistance to pressure during shock load in an off-highway operation. However, my choice is still synthetic due to the superior lubrication, especially to the pinion bearings, in a marginal situation.

On your Bronco, 20 degrees sounds pretty darn high. Keep in mind that you actually want to run the pinion at a downward angle about 111/42 to 211/42 degrees to allow for pinion climb.

And I do hope that you're talking about the rear end. That much pinion angle on the front without cutting and turning the steering knuckles will put them at a negative caster angle and make the vehicle undriveable.

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