49TT - According to information in a 1947 GMC Maintenance Manual, which better details overhaul/repair of both the small 7" and large 9-1/2" diameter hydrovac units, it says to tighten the 4 cylinder shell securing hook bolt with nuts and lock washers. Then tighten hook bolts on the small 7" units to 24-28 inch-pounds. That is followed by "CAUTION: Do not over-tighten hook bolts." *
To the best of my knowledge, these hydrovacs where the same as the Chevrolet units, so the technical info should apply as well.
* Note - For the larger 9-1/2" diameter hydrovacs, the instructions indicate the hook bolts on those units are to be tightened to 5-6 foot-pounds.
