Hey PYandre,
Welcome to the near death experience of bridge mode in Telmex routers! It can often be hit and miss depending on the line and router model. Here are some tips:
1) You need to request a separate login and password for the PPPOE login credentials for your Google wifi points. The password on your current router is encrypted and not transferable. They will give you one.
2) Telmex doesn't give tech support for bridge mode, at least not for residential customers. You're on your own. But there are resources on the web and youtube. Just google "modo puente" Telmex, etc. You can also try to find the manual or similar. Also a crap shoot. In most cases, you go to WLAN page and select "modo puente"...thats its. don't change anything else.
3) Telmex routers keep the IP address active so you can log in and change it back etc. The default is 192.168.1.254. Which means, as in the earlier posts, you must assign a different gateway address to the google router. You can then put another Telmex router port directly on your LAN and access either. But can be tricky. Make sure Telmex modem DHCP server isn't on, with two servers assigning addresses on your network.
4) Sometimes, Telmex lines simply will not go into bridge mode with foreign routers. I've done traces on the PPPoE connection between the modem and external router and the broadcast packet never gets sent out by the modem to the router. But same in router mode connects instantly. No explanation. Some modems don't go into bridge mode. I think my Arcadyan's wouldn't. Huwaei worked better, but not always. You can buy different modems on Mercadolibre cheap and try them. Also try Telmex and ask...things do change...
good luck,
Tom