Grohe shower check valves

I'm trying to replace a Grohe shower cartridge (four directional). The one thing I can't seem to get is how to get the check valves in place. For the cartridge I'm replacing, the check valve is already in place on the hot side, but is missing on the cold side. When I insert the check valve on the cold side, it does not insert fully, and just sticks out into the open space for the cartridge, preventing me from re-inserting the cartridge. Any assistance appreciated.