Can a vacuum leak cause spark knock?

Previously, I could never get the timing set right to eliminate spark knock. It would usually spark knock when going up hills at 45 MPH or so. It has always had a leaky power brake booster. Recently I replaced the booster which eliminated that leak, and now there is no spark knock. I was thinking that maybe the vacuum leak was preventing the distributor's vacuum advance from working correctly, but my friend said that if the vacuum advance wasn't working correctly, the timing would stay retarded, and retarded timing doesn't cause spark knock.

A vacuum leak would cause a cyl or 2 to run lean and running lean could cause the knock.

Agree!

R.