The invention relates to a device, a process and an apparatus for manufacturing a silentblock device having a silentblock (4), a seating (2), a shock absorber (3) and a casing (1) having first joining means (120) between the casing (1) and the seating (2) formed by a frusto-conical portion (121) in each end of the casing (1) and a conjugated frusto-conical portion (122) in each end of the seating (2) to clamp the seating (2) to the casing (1). The apparatus has: containment devices (100) for defining a cavity (110) between the surface to be over-injected and the containment devices (100); entrance devices (200) in the containment devices (100), so that the over-injection product can be introduced in the cavity (110).