Ray,
If you shim the rack , and a small shim there is not a bad thing, you want to use a full strip of shim under the entire rack surface and it won't be very thick. Do not try to just shim under the bolts. ( I've known someone who tried that and it is not nearly as good.) You will always have a little play. It can't be too tight or you will get spots that bind.
Mark
Thanks for the info Mark.
My common sense thinking tells me that a full strip shim is the way to go.
I've never considered shimming just under the bolts, doesn't make sense to me.
Thanks for the confirmation.
Ray