was it recirculating ball or balls?

 

Richard, it's a screw and nut setup vs a gear.

 

Just ball. Not recirculating balls.. get your mind out of the gutter.. just joking =). Anyways this link explains it better than I can. Very detailed with pictures and everything.

If Im not incorrect (which I am too often) rack and pinion gives a much more direct feeling b/c of the lesser amount of parts in its composition. It is however harder to operate bigger/heavier cars using it.

http://www.autoweb.lycos.com/garage/subsys...ys/basteerb.htm

 

A ball screw actually has several balls so you are half right either way. The ball screw is composed of a worm gear (think of a shaft with a spiral running down it), a pillow block, and several balls, the balls being retained by the pillow block. The balls ride between the gear and the pillow block to allow a larger surface to distribute load between the two components. They are used for high load applications (usually). Rack and pinion on the other hand, is a rack with teeth and a set of splines on a shaft. The splines mesh with the teeth. The profile of the teeth on both the pinion and the rack are critical. Surfaces are Nitrided for wear. If they are not perfect, point loading will cause excessive wear. Rack pinion is far superior. Also much more expensive to manufacture.

As a side note: The Alaska Airlines MD-83 which crashed into the Pacific Ocean had an "Acme Screw"...a ball screw without the balls. The wrong grease led to excess loading, subsequent galling and the loss of the vehicle.