Master cylinder Firewall Hole

[Big Fenders]

I've got a project Suburban that I have to make a master cylinder plate to cover the two holes in the firewall. This is a 1960 GMC. I do need to bore a hole for the brake master but since this sub is about 250 miles away from me I need to know the size hole to bore in the 1/4 inch plate...easier to do here in Tucson than there. Thanks Bob

[DPowers]

Contact CaptainFab- I would think he could assist.

[markeb01]

Can’t confirm the hole diameter in the firewall, but I can confirm the hole in the plate sold by Master Power Brakes. It is 1 - 13/16” as shown in the attached photos. I ran this plate on my truck for a few years when I ran a Turbo 350 in my 1960 GMC. Eventually I went back to a manual 4 speed and fabricated a larger custom plate to accommodate the clutch master cylinder. If you want to save some effort you can have the plate for the cost of the shipping, or I can post a tracing of plate with dimensions if that’s helpful. If you’re interested shoot me a PM.

[jbgroby]

This is the plate from Capt. Fab.

It be pretty,arrrrrg (Pirate talk for Capt. Fab)

[Captainfab]

Thanks for the plug guys

The center hole in the plates that I make is 2-1/16". This is close in size to the hole in the firewall.

[53lowdown]

Sorry to hijack - but why does the Power Booster have to be tilted up like that on these trucks? Is it a clearance problem with the engine or manifolds? The manual master cylinders sit square with the firewall so it can't be a brake rod alignment issue.

[Captainfab]

You know, I don't know of a reason for it other than keeping the master cylinder level, as some stock trucks were higher in the rear. But then if you look at the '67-'72 power brake setups, the master is tilted towards the front. Now the trucks starting in 1988, have the booster bolted directly to the firewall which positions the master basically cylinder level.

I designed my power brake booster brackets with a slight angle upwards simply because it just looks right to me.

Originally Posted by 53lowdown

Sorry to hijack - but why does the Power Booster have to be tilted up like that on these trucks? Is it a clearance problem with the engine or manifolds? The manual master cylinders sit square with the firewall so it can't be a brake rod alignment issue.