I bought my 91 z28 last summer and it had tons of stuff done to it. It has a underdrive pulley(sheave or whatever) setup on it and once the car drops below like 1200 rpm or so, the power steering goes away. I was fine driving it like that cause I'd just rev it up in the corners. Then I bumped a curb cause the power steering went away half way through the corner. Is this due to the under drive pulley setup or something else? Does anyone have the stock diameters of the pulleys so I can compare them to mine? Thanks

 

I'm allmost certain it is the underdrive pulley. I would put the stock one from a junk yard on to see if it fixes the problem. Also check the P.S. fluid level and belt tension.