It all started with a clogged rear differential vent.
I noticed some gear oil on the inside of the rear tire so I inspected the vent tube an found it to be clogged. After removing the tube and clearing the clog I then cleaned off the rear tire. Some time after that I saw fresh oil on the inside of the tire again.
Thanks to this site and all the great people here I was able to decode my axle and order the correct size axle seal.
During the removal of the drum I discovered the brake shoes were saturated with oil, this prompted me to do the brake job that I was holding off until next summer.
New shoes, new wheel cylinders, new lines, new hoses and conversion to a dual chamber master cylinder!
During removal of one of the front wheel cylinders I discovered it to be leaking, not much just a little damp at the front piston!
I check the brake fluid every couple of months and never noticed it was going down?
Here on FTE, I read that a 67 to 73 F250 4x4 drum/drum master would bolt right onto my 66 so I went down to Advance Auto and found one on the shelf for under $23.00. I needed two brass adapters and I was on my way.
As you can see from the photos, the adapters are both 3/8-24brake line to 9/16-18 and 1/2-20.
The new master came with a much longer push rod. I decided not to use this because I already had two holes in the brake pedal and it was to long for both. The push rod on the truck was in the front hole and was 1/2 an inch to short. The bolt holding the rod to the pedal has an eccentric cam, to which the push rod attaches to allowing over a 1/4 inch of adjustment if needed.
I fabricated a short slug using a 5/8 in grade 8 bolt, rounded one end and drilled out the other. The slug is 1/2 in long and fit nicely into the master allowing me to reuse the flat rod that was on the truck. see pic.
All said the work took me two 5 hour Saturdays with the help of my youngest son to bleed the brakes.
I now have the added assurance of a two reservoir master!
And as for the brake light switch, I reused the brass four way cross (tee)that split the old line to the 4 wheels. I place this cross (tee), coming off the master for the front wheels, one line for each front wheel and one line going to the pressure switch.