My 71 spider had an episode of 'hard brake pedal/ loss of efficient braking'. It was a two-off event, and I have not been able to replicate it other than to remove the vacuum line to the booster. Seems unlikely that I lost vacuum for those two events, car was running great and the hose is new, master is new, booster is what came with the car but seems to be working (mostly!)
So I pulled a ATE booster out of the cabinet to see if I could conjure up a scenario where this might occur, and I THINK I might have found one.
The booster has a metal rod that is firmly connected, and runs through a plastic cylinder (about 2 inches diameter) that sits on the pedal side. In order for the booster piston to travel in and out, this larger diameter rod passes through a seal on the pedal side, moves in and out, and the cylinder is actually what attaches to the diaphragm in the booster body.
If that large diameter cylinder got hung up (off angle and / or binding) we would have a stiff pedal. Seems logical and reasonable that the metal rod (concentric to the larger cylinder) needs to be free to move in and out of that seal,
The plastic cylinder is under the accordion boot on the pedal side. I wonder, should the OD of that cylinder be lubricated to make it easier to pass thru the seal, and to reduce any off-angle loading? If yes, what lubricant to use ? Seems to make sense again since the cylinder is under the accordion bellows and thus protected.
What say ye? Silicon based oil ? Teflon grease? I do think this is likely my issue on the spider as there is nothing else that moves except this rod/cylinder.
74 GTV with 10548's and Ingram pump
71 Spider 1750 BOMBER ; 1995 LS 78K tight fast car