Squeal is often generated in car disk brakes. It has been found in previous studies that two types of squeal exist in disc brakes. One is called out-of-plane squeal, and the other is called in-plane squeal. There are many reports that treat the out-of-plane vibration modes among the disc and caliper due to Coulomb friction. Previously, the authors have experimentally and analytically confirmed the out-of-plane squeal generation mechanism and countermeasures in rigid and floating types of car disc brakes. Recently, the occurrence of in-plane squeal has been increasing. This paper deals with two types of disc brakes that generate both out-of-plane squeal and in-plane squeal. The vibration modes of the brake units during squealing are also investigated. Additionally, the relationship between the rate of squeal occurrence and both the direction of disc rotation, the disc rotation speed and the pad pressure are in investigated. And the effect of the rubber installation to the pads on squeal is also investigated. From these experiments, it was clarified that in-plane squeal have four characteristics as follows. The squeal frequency is 10195 Hz, vibration modes of the brake units during squealing are 2nd in-plane mode, the area which is squeal occurs, varies with the rotational speed and the brake hydraulic pressure, it is because having a negative slope coefficient of friction, the squeal occurs when the disc rotates positive, when the disc rotates negative, squeal does not occur. On in-plane squeal, even though installs the rubber to either in-plane and out-of-plane direction, the effect of resonance can be obtained to in-plane squeal. Thus, for the in-plane squeal, pad is an important factor.