I want to put a switch between them so i can connect an older time capsule to it.
Sorry, but you cannot locate a switch between a modem and a router (Time Capsule). The switch must come after the router on the network, not before it.
The reason for this is that the modem only has one IP address to deliver. If you place a switch between a modem and other Ethernet devices, it will be a matter of chance as to which device receives the IP address. Other devices will not be able to connect to the Internet.
Your network should look like this:
Internet > Modem > Time Capsule > Switch > Other Ethernet devices