The Mk4 car's gearbox is supported by an additional bolt on cross-member running from front to back of the engine bay at the bellhousing position. This bolt on cross member, incorporating two rubber mounts and known as the gearbox cross member, is fixed in place to the shell by four bolts (two in the front cross member and two at the base of the bulkhead) and to the gearbox by lower bell housing bolts. Due to the fact that it locates onto the gearbox by utilizing the bell housing bolts it is possible to fit a Mk3 gearbox to a Mk4 car.