The Ford Barn - View Single Post - Treadle Vac

alcan · 06-21-2012, 12:29 PM

I have run into this problem a few times years ago. The cause was the master cylinder had too large a bore size for the design of the booster unit. Usually it was because a master cyl for a manual brake car was installed. They look identical and bolt right on so it was easy to do. Ford ( and others ) masters normally used a 1 inch bore but in 1958 some models of power brakes had a 21/32 inch bore. The smaller bore reduces the hydraulic line pressure to the wheel cylinders; in this case by about 30%.

06-21-2012, 12:29 PM	#3
alcan Junior Member Join Date: May 2010 Posts: 10	Re: Treadle Vac - compensating valve? I have run into this problem a few times years ago. The cause was the master cylinder had too large a bore size for the design of the booster unit. Usually it was because a master cyl for a manual brake car was installed. They look identical and bolt right on so it was easy to do. Ford ( and others ) masters normally used a 1 inch bore but in 1958 some models of power brakes had a 21/32 inch bore. The smaller bore reduces the hydraulic line pressure to the wheel cylinders; in this case by about 30%.