We moved my brother's W116 300SD up to our new house a couple of months ago. It had been sitting a while because work swapping the ACC to manual climate control has been slow because we haven't had the time to do much with it. Before we moved it, it had lost all brake pressure so we figured the master cylinder had gone bad. The brakes had been totally redone besides the master cylinder (new lines, discs, pads, and rebuilt calipers) so we figured that was the issue, we swapped in a known good one from a parts car, bled the brakes and drove it up. We had to move it recently and it has lost all pressure again.

Any ideas as to why this would happen? I'm thinking maybe one of the rebuilt calipers is shot but any other insight would be nice.

__________________
Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.