Why does my 65 firewall have 8 holes at the brake area?

cdnpont · Canadian Poncho Superstar!

Why does my 65 firewall have 8 holes at the brake area?

norontcan · Canadian Poncho Superstar!

With the car in storage I wasn't able to get around it enough for a good identification
However, the top 2 holes ( left and right ) have studs coming from under the dash onto which are screwed flanged nuts.
Don't know what that gold thing is in the bottom right as mine has a black plug in that location. The larger hole above the gold thingy is for the speedometer cable.
Mine is a P/B car.

cdnpont · Canadian Poncho Superstar!

It's just the two from the bottom that are a mystery to me. The other 6 I know what they are for.

cdnpont · Canadian Poncho Superstar!

I should have thanked you for your reply Ted.

Was there different boosters in use? One that used the upper combination of 4 holes, the other that used the lower 4? I've not seen any description or any images of the use of those "two from the bottom" holes.

Any GM documents I've seen always show 6 studs. And most all brake pedal supports seem to have 6, not 8.

So c'mon guys, what are those two mystery holes for?

4SPEED427 · A Poncho Legend!

I believe they used 2 booster styles, Bendix or Delco Moraine but I have no way to prove if they used the same holes. Time to start looking at pics online.

cdnpont · Canadian Poncho Superstar!

I've studied images of 1965 B Body Chevrolets with manual masters, and none I can find have those extra holes on the firewall. Only dimples.

My 65 has the 8 holes.

If the different booster used the upper set, then would the rod and clevis from those also have to line up with the upper hole in the brake pedal lever?

Mundane question, but I've wondered about it for a while.

Cheviac · Guru

Perhaps holes for the rubber plugs that secure the firewall insulation to the inside of the firewall?

4SPEED427 · A Poncho Legend!

Yeah, I just don't know. I've never messed with brakes on these cars at all other than changing master cylinders.

cdnpont · Canadian Poncho Superstar!

Holes for plugs is plausible, but they would be right into the booster back when it's mounted.

When I talk of the upper and lower 4 hole combinations, I mean the top (yellow) which would include the mystery holes with the red dots, and the lower in pink.

Any cars with boosters that I've had always so far (3) use the lower (pink combo).

Image with the lower 65-66 holes filed out to accommodate a 67 and later booster. 11" in this case.

And we could go deeper,

Why did those lower holes move outward in 67? You can't fit a 67 and later booster on a 65-66 firewall without some filing out of the firewall and pedal brace. But you do so and it will fit. And a 65-66 booster won't fit on a 67 without doing the same in the opposite direction.

Simply a design change? Seems weird to change the stud spacing except to exclude the use of an incorrect for that year booster. Was that done to keep any leftover 65-66 boosters off the 67?

I have too much time on my hands. I'm board. Sorry.