Y'all may find This Tech Tip handy
http://www.stovebolt.com/techtips/bendix/erickson/
Surprised no one linked to it earlier in the thread, or is it already on the required reading list for you hydrovac folks?

Grigg


1951 GMC 250 in the Project Journals
1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-