Hello everyone. I'm taking the car in tomorrow to get rid of the backlash in the driveshaft. If they end up denying me warranty coverage, what can I expect to pay?

Jon

 

There is supposed to be backlash. It's a defined amount

 

even if you switch it to an aluminum one, there will still be take-up slack in the drivetrain.

 

Yep there's got to be some backlash. On an 8.8 anything up to .012" is just fine. As some others have posted some backlash is neccesary to ensure a proper wear pattern. With no backlash your tooth contact pattern would be so far off you'd destroy your ring and pinsion in a very short time to say nothing of the whine that would cause.
Check the specs that Ford publishes and you'll see it must be within a certain range. As long as it's in the range you're ok. Basically if you set up your gears with the right contact pattern the backlash should be within spec.

 

All cars have some, its just that the Mustang's components are much larger then its contemporaries(and most import SUV's and trucks) and the the 3650 is a beefy transmission that makes a lot of noise right next to your leg.