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Discussion Starter #1
Hi all, I just installed a new dual reservoir master cylinder on my '66 GT and wondering if there is should be some type of seal between the master cylinder and the firewall? From the corrosion/staining it looks like there had been previous water or other infiltration into the passenger compartment through either the master cylinder hole and/or the steering column hole in the firewall.
The hole in the firewall is 2" diameter and the rubber boot for the master cylinder pushrod is only 1-5/8" so there is nothing but metal to metal contact now and nothing to really seal off the passenger compartment from the engine compartment there. I haven't see any other gasket specific for this application. Am I missing something or should I just either cut a gasket or wipe the surface with some black RTV?

It's a '66 manual disc brake GT car and the new master cylinder is for a '74 Maverick manual disc brake car.
 

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1966 Mustang Hardtop 289 4 Speed
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I have some gasket material in the garage and actually thought about making a thin gasket before I installed mine but never got done. I don't ever recall a discussion on it for that matter. It does kinda make sense though.
 

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Discussion Starter #3
Yeah, I didn't really come up with anything searching here. Googled master cylinder mounting gasket and one comes up for a '63-76 corvette, but no Fords. Not sure if the dimensions are the same or not.
 

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They are not, but they are close. I have installed correct Ford type master cylinders on repro boosters in place of the GM style master cylinder, all it takes is a little filing. Installing such a gasket would be no challenge.
 

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I don't believe I've ever seen any kind of gasket/seal around the master cylinder hole (though I have seen a rubber boot around the steering column).
 
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