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Just trying to get some info on this brake booster as I have never seen one like it before. Unless it is something else. It's in a 1964 M350.
Hydro-Vac (aka remote mounted) Power Brake booster. These were used on vehicles when the drum type of booster couldn't be mounted on the firewall due to clearance issues.
Found mostly on the left frame rails of trucks, but 1955/57 T-Bird's and some 1961/64 Galaxies with A/C came with Hydro-Vac's which were mounted on the left fender inner aprons.
With respect to '61-'66 F-100s through F-350s, I've only seen this style thus far on F-350s. Coincidence, Bill, or is that the usual application for the Hydro-Vac units on these trucks?
(I sometimes wish my '61 F-350 had power brakes, which may be why I notice F-350s with boosted brakes. If I were adding them, however, I'd want to add the Hydro-Vac style, to keep a stock appearance.)
No steve it isn't drivable, but it does run. I bought it for the cab. No rust and the rad support is in perfect condition. Obviously the truck wasn't driven much. 74000 miles. Plus with 5.13-1 differential gears I don't think it was very fast. The headliner is as good as the day it left the dealer. I was very fortunate to find this truck at Picn Pull. Was on the way to be crushed. These big RVs don't make it into the yard because they can't prop them up off of the ground safely. So they somehow tear them down. Probably with pay loader. Anyways I'm glad I got it. ,Doug.
Actually in amazing shape from an originality perspective. And a Custom Cab to boot. My '61 F-350 has its original 5.13, and it's, surprisingly, quite driveable (optional 19.5" rims partially compensate for the stump-puller diff).
Anyways I'm glad I got it. 
,Doug. 
