[Keith Seymore]

Some of you know that I was a brake development engineer for GM light truck at the Desert Proving Ground in the early 1990's timeframe. My (professional) experience is therefore limited to dual systems but hopefully it is still ok for me to make some general observations:

a) Not to put words in mkoser's mouth but it seemed implied to me the thread was to discuss drum/drum systems. References to disc/drum systems tended to confound the issue and probably should have been avoided.

b) References to the master cylinder port location should be made from the perspective of vehicle position. That is, the front port is the one closest to the front bumper; the rear port is the one closest to the rear bumper. Any other frame of reference causes additional confusion.

c) In my development experience, even within modern dual systems, there were some that were front to front and some that were front to rear, depending on other considerations like hood clearance and relative reservoir size based on vehicle platform* In those cases it was obvious what the intention was, since the large reservoir would be for the front disc system. My point is that I wouldn't be surprised if early cast iron dual master cylinders had similar variation and it would be ideal if the part itself could tell us which way it was to be hooked up, similar to my aluminum master/plastic reservoir analogy. Since we are specifically discussing a '69 Bonneville m/c I wonder if the '69 chassis manual would provide any insights...

d) I have the brake system release charts for all LD pickups, starting in 1969. I'll take a look and see if they reference which port feeds which brake system (front to front vs front to rear).

e) I believe this thread was an excellent resource and am glad it is still available as a reference.

K

*example - the old M/L Astro/Safari mini van. The sharp hood angle cause the rear reservoir (located toward the front of the vehicle) to be miniscule in height. I tried one of these master cylinders on my Chevelle and, while it worked well for pedal feel/effort/travel, the angle of the installation meant that I had to jack the rear of the car up in order to put brake fluid in the rear system or to bleed the brakes.