Weird Steering Issue

[SuperCoupe400]

I've been noticing a really disturbing thing that only seems to happen on very tight, slow speed turns (like when i'm doing u-turns in a parking lot, or backing into a parking space with the wheel fully cocked to one side or the other). The front wheels feel like there may be some sort of linkage failure - the same type of occassional jerky slippage you would feel if your front wheel drive car had a bad CV joint.

I used to think it was one of the tires slipping sideways over loose branches or rocks in my driveway as i turned real sharp, but i've noticed it happening even on perfectly smooth asphalt. Anybody else experience this? I changed my front brakes and rotors recently and i'm certain i tightened all the lugs down good, so i don't think it could be the result of a wheel that's not on tight.

thanks.