Not my first rodeo replacing the mechanical vacuum pump. Here’s my post on the subject: http://boondockdad.com/vacation-save-or-how-i-repaired-bad-brakes-300-miles-from-home/ from last year.
But, I was a little sceptical it was the vacuum pump, again. Bad power booster, or check valve will have same symptoms. So, this time I checked what kind of vacuum the pump was producing. The ‘thumb test’ was inconclusive. There was vacuum, but I couldn’t be sure how it compared to new. $15 Harbor Frieght Vacuum and Fuel Guage was telling me 5 in-Hg at idle, and 15 in-Hg at 2100 rpm.
Since, there’s no spec in my genuine Ford Service Manual on what vacuum should be, I had to compare it with generic engine numbers; and those are waaay low. I’m reading it should be minimum 20 in-Hg at idle.
Pulled the pump. This time I didn’t remove the radiator shroud. I left the pulley on the pump, and backed out the mounting bolts with a ratcheting 10mm crescent. Exchanged at the local Autozone- it was a lifetime warrantied Dorman. Too bad my time and trouble isn’t covered, but then they wouldn’t be able to keep stamping out this cheap CHINA crap for a profit. Original purchase price was $110. The Motorcraft is $300.
All back together, brakes have full power assist, with the pump producing 25 in-Hg at idle.
See You Down the Road!