Continual Failure Of Belt Driven Vacuum Pump
I have a 1999 E-350 with a 7.3 liter Power Stroke. The engine mounted vacuum pump that originally came on the van lasted about 9 years but none of the replacements last even one year. I've had to replace it 3 times already and the third one just failed again causing a loss of the power brakes. I've put on rebuilt pumps each time and the latest one is a Motorcraft.
The pump doesn't seize up, it just stops producing vacuum. Putting on another pump makes every thing work fine but only lasts 8 months before failing again. Any ideas?