I agree with sixtyfiver check you housing at the lever. some older (first gen?) Dia Compe lever required a very special ferrule on the end of the housing. pull on the lever and look behind it where the cable comes out and be sure the housing is not pulling through. also you housing looks real short. a third or fourth or a friend is called for.
there is a small trick using the QR but it takes a bit of practice
BTW that is a great looking Delray. I worked on lots of those when I was living in the Quincy area years ago. a bit of elbow grease and some pledge and it will shine up real nice
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk