what tools does one need to remove rear calipers on 1992 buick riviera

Standard auto mechanic hand tools, but not necessarily all the tools mentioned here.

Ratchets
Wrenches
Screwdriver
Hammer
Torx tools
Allen wrench tools

If you plan on replacing the caliper you probably wont need it but if you are going to reuse the caliper it will be best to have a caliper tool to turn the piston back in. This is a racheting caliper. This type of caliper is also part of the parking brake system. DO NOT try and push the piston back in like you would on some calipers. If you don't have a caliper tool you may be able to rent or borrow one from a parts store.

Sorry, but I didn’t think I had to be that explicit. For some reason I thought that since you were asking about what tools are necessary, I thought that you realized that the conventional C-Clamp method of retracting the piston back into it's bore couldn't be used here, and if used it would cause caliper damage. Inward pressure must be maintained on caliper piston while it was "turned" back into it's bore. The link below shows you the tool you need.

http://www.denlorstools.com/home/dt1/page_2453_159/lisle_lis28600_rear_disc_brake_piston_retraction_t.html

Good job Bill. Let us know in the future if you need any help.

You got it Bill. :-)