Fig. 3 Ventilating CV boot
Attaching the CV joint boot onto the outer body of the joint frequently requires compressing or squeezing the boot. This produces a vacuum in the joint boot, which may cause a crease to the inside when driving (arrow).
For this reason, after installing the joint boot, vent it briefly by letting some air in at the small diameter end, thus creating a pressure balance and restoring the correct boot shape.