How to get the private keys out of old wallet.dat without syncing blockchain
From bitcoin-qt, click Help->Debug and open the Console tab. Type in dumpwallet &lt;outputFileName&gt;, making sure that of course, the output filename isn't wallet.dat or it may overwrite your wallet.

This command creates a plain text version of your wallet with all private/public key pairs in WIF format.

You may need to configure your clients to point to the correct directory containing your wallet.dat with the -datadir command line option, or if you have a custom config file use -conf.

You can also use the dumpwallet command with bitcoin-cli if you have a bitcoind running.