What rear do you have? I have a Moser Ford 9" with a WaveTrac. I used the oil that Moser recommended. I still don't have my car finished so I couldn't tell you how it drives, but thanks for the info. Hope it's not an issue with WaveTrac.
Why/how could the oil make a difference? And when you say "side to side" Do you mean right side will hook/spin and the left side does nothing and then the left side will hook/spin while the right side does nothing? Almost like it's not a posi rear.
I use a Moser 12 bolt.
As far as how/ why oil matters... this is off the website:
"If you are racing your vehicle, and wish to upgrade the gear oil to improve performance or durability in racing conditions, choose the oil carefully: be aware that some gear oils have additives that are not recommended for use with your Wavetrac®.
Some have friction modifiers designed for limited slip differentials. These modifiers generally increase slipperiness and are intended to reduce clutch disc chatter in conventional clutch-type LSDs. Some gear oils such as Red Line Oil’s Shockproof® type have microscopic solid particles in immersion in order to “cushion” transmission components, acting as an extreme pressure agent.
The Wavetrac®, and all helical gear differentials in general, operate using friction. The friction generated between its internal gears and its housing are what allow this type of differential to function."
Regarding the last question, it's a very quick and rather violent shift from side to side. At no point is one tire allowed to spin while the other does nothing for any prolonged period, more like it happens for a split second on one side, then shifts energy to that side, then back to the other side. I let off every time it does this, so I can't tell you how long it would go on if I allowed it to. And, it did not do it every time, sometimes it would work perfectly, it was bizarre. I do believe the fluid used by the p.o. was probably limited slip fluid, and this was causing the issue, as stated above, I've hit it a few times (once again yesterday) and so far so good. I wouldn't worry about yours imitating mine, as long as the proper oil is used. This does not seem to be a common issue, and the Wavetrac appears to have a solid reputation from what I have read.