When kinking, flattening or rippling of larger size conduit is resulting, it’s best to replace the rollers before replacing the clamping jaw. Usually the rollers have worn out or have gouges in them and are just due to be replaced.
Also, make sure that there is an ample amount of conduit sticking out past the clamping jaw. If the end of the conduit is too close to the clamping jaw, it will start to flatten the conduit as it is bent due to the force being put on the conduit.
Aim the seam of the conduit away from the bending shoe. Occasionally, a small amount of lubricant, such as WD-40 may be required.
Gardner Bender FAQ 