rjl, are you running a 710? Like crashed_1 mentioned. yes the rear diff outdrive on the rear ball diff unit wears. I guess the right side first and eventually the left. I just had both of mine replaced after a few good gallons of racing.

It would be good if Serpent came out with the spring steel option. The pin in the dogbone will make a dimple inside the outdrive and cause the rear wheels to hop or jump when you accelerate. I believe this is caused by the dogbones getting trapped in the dimple and does not move freely. It will come to a stage when the rear suspension binds. So sometimes you'll find the rear end of the car just spinning off when you turn for no apparent reason.