Disc Brake Hold Off Valve

'67 Proportion valve in and out shown here
http://www.imperialclub.org/Repair/Lit/Master/233/page12.htm
'69 should be the same.

A metering (also called hold off) valve was used on the floating caliper intermediate cars, and some others, depending on the year. Not on kelsey Hayes set ups.
See here:
http://www.imperialclub.org/Repair/Lit/Master/274/page12.htm