Will the Larger Master Cylinder also 'mount right up - bolt right in' place of the stock one in an '85?
Even though the stock one is fine... is it no biggie to upgrade - replace the Master Cylinder while we're at it, too?
Yes, the master will bolt right in, however...
Having done this upgrade as a result of the answers in this thread (Thanks for all your help everyone!) and other research, I would recommend _not_ upgrading the master cylinder until/unless you also upgrade the rear brakes to disks. Together, even the four-large-cylinder type calipers (sold by Marlin) and the stock rear drums do not take enough fluid to work well with a 1" master cylinder. A bigger master cylinder actually hurts overall braking unless it's matched with appropriate calipers/drums.
I pulled the MC and booster out of a '97 T100 4wd expecting to use both. Ultimately, the T100 boster was enough bigger in diameter that it interfered with the steering shaft (and, to a lesser extent, with the clutch master), so I went back to the stock booster. I'm going back to the stock size MC as well. The pedal position is good - there's no question about it going to the floor - but the braking effort currently is much more than it was. I really have to stomp on the pedal to lock the fronts up, enough that I would be nervous letting my wife drive the truck. I was counting on the additional boost from the larger, dual diaphram booster to compensate for this.
It's simple enough to change out a master later; try the caliper swap first and see how the pedal feels. I think you'll be happy, have better overall brakes, and have more $'s for something else. My $0.02.
