Remove all the items on your bookcase and put them to one side. Move the bookcase away from the wall to determine how the base rests on the ground. Wobbly bookcases are often caused by tack strips installed around the perimeter of a room. If the bookcase rests on top of the strips, it will lie in an unstable position and cause instability.
Pull the carpet away from the tack strip. You should now be able to see the padding between the carpet and the floorboards.
Measure the width of the bookcase at the base of the unit. Measure out the same distance from the back of the tack strip, where it connects to the wall, out onto the floor padding.
Mark a point on either side of the padding using a marker pen. These positions are where the frontal area of the bookcase base will rest once reinstalled.
Cut out two segments of padding measuring around three inches in length by two inches wide using a utility knife. Put the padding fragments to one side.
Fit the wooden shims into the spaces in the carpet padding. The shims should have the same thickness as the tack strips. This will ensure the bookcase rests level once reinstalled.
Lay the carpet back over the padding. Move the bookcase into position. Check the unit is evenly set using a level before packing it with books.
Install adjustable feet at the base of your bookcase if your house has hard flooring. You fit adjustable feet, also known as gliders, to the bottom of bookcases and they allow you to adjust the height of the unit. To begin, drill a hole in each of the four legs of your bookcase. If your bookcase has two feet that run the width of the case, drill a hole at the top and bottom of each leg.
Connect the adjustable feet to the legs of the bookcase. Adjustable feet are usually constructed from metal and you can screw them easily into the base of furniture by hand.
Position your bookcase against the wall once the adjustable feet are fitted. Use a level to check if the bookcase is evenly set on the ground.
Balance the bookcase by continually adjusting the feet until the level gives an even reading. You can adjust the feet by tightening or loosening each fitting to lengthen or shorten the size of each foot. Even if your flooring is uneven, your bookcase should evenly balance once you have properly adjusted the feet.