On my volvo I got the tie rods replaced for $330. After they got replaced, the steering wheel started to shake real hard when turning right or left. They told me that it is the Steering rack and that needed to be replaced also($740.00). Why did it start doing that after I replaced the tie rods? Why not before? Is replacing the steering rack called the rack and pinion?

 

If there was play in the old tie rods then that might be why you didn't feel it.
Once they were new and everything was tight then you could feel what the rack is doing.

Yes it is called a Rack and Pinion.

 

the mechanic said i should just drive it(since it isn't that bad yet) until the steer rack brakes(goes completely bad). He said it won't hurt anything else. Is this true? Or is this something I need to fix right away?