A pneumatic brake booster includes a drive piston actuating a master cylinder by a push rod while being returned to rest position by a return spring. The brake booster has a vibration damper having a part made of an elastic material working compressively, of overall parallelepipedic shape, with a length greater than the spacing of two coils of the spring prior to its installation in the brake booster and whose front and back faces are equipped with a longitudinal slit penetrating the material mass of the damper for engagement by way of those slits on the two coils of the return spring.