What is axle wind up and how does the car act when this happens?

Is the axle twisting? Moving in a horizontal or vertical plane?

What prevents this? LCA?

 

Are you talking about axle wrap?

 

+1 You mean axle wrap?

 

If you are talking about axle wrap..... Think about what happens when power hit the rear axle.
Either the tire turns (Pushing 3700 lb) or the axle turns the opposite direction from the tires.
If there is anything that gives (rubber bushings, LCA, UCA, UCA Mount, Mounting points, etc) this can
cause a deflection, release, deflection, release, etc that results in wheelhop. Depending on suspension
geometry this also causes the backend to squat as the suspension is compressed and the tires try to
lift up off the pavement.

If you are in a forward gear the noise of the differential tries to rotate up and over.
If you are in reverse it tries to rotate down and under.

If you have ever seen a leaf spring car with Slapper Bars at the track think about how they come up
and contact the spring eye when power is applied. This is because the spring deflects when the axle wraps
and the slapper bar uses this force to lift the whole body and force the rear tire down into the pavement
and at the same time place a limit on axle wrap stopping the deflect and release cycle.

 

We always called em traction bars.

 

Slapper bars and traction bars are two different things. They serve the same purpose but two different things.

 

Same same. http://www.competitionengineering.co...s/chassis2.asp