And it is possible to backup wallet.dat and then upload it into bitcoin cash client? Cuz seems I can not figure out how to check the addresses and understand is there was bitcoins on 1 august 2017.
You don't need to import wallet.dat file on Electron Cash wallet, you only need to export Private Keys for addresses which has BCH and import them into your Electron Cash wallet.
here are detailed steps for how to claim your BCH :
https://bitcointalk.org/index.php?topic=2078292.0