I am converting the brakes to power in my 69. I have the 4 holes in the firewall, two holes for studs for the original M/C, and two more threaded holes on the bottom that held the steering column support in. My question is which holes do I keep as the 4 do not line up with the booster.

 

69vetteL46:

I just did this exact same conversion on my '70 last weekend. Boy, are you in for fun!

OK........none of the 4 holes you have work. If you look at the studs on your power booster you'll see that they aren't on the same centerline as main bore for the booster. Now look at your firewall. You will need to maintain the large hole as a working point, as it will line up your pedal rod and clevis with your brake bedal. I had to use a grinding stone on an air powered die grinder to enlarge this hole to permit the booster with rubber dust boot to pass thru without binding. Once you get this center hole large enough, you'll need to hold the booster in place and mark the locations of your 4 mounting studs on the firewall. I used a small 6" long carpenters level across the front master cylinder mounting studs to assure that the booster was being mounted level (2 people for that step would really be nice.....you'll see what I mean). Here's the kick in the butt. The pedal housing that bolts up to the firewall/birdcage is different for a non-p/b car than on one with p/b from the factory. The top is narrower on a non-p/b car. Hope you get the booster studs marked so that you'll have access to at least one of the top studs from the inside.

I removed my speedo/tach dash pad, steering column, column mounting brackets and still had a bitch of a time getting at the top studs on the interior to tighten them.

I actually used a thin grinding stone on the new top right mounting hole to grind away a portion of this pedal housing just to permit the stud to enter the car.

All told, I have about 16 hours into that upgrade. I wouldn't do it again unless I could get the proper pedal housing to install.

If you need to chat about any other specifics, email me at: kosick@comcast.net. Then I could give you my phone number and we can chat in more detail.

Bottom line, this is not a simple bolt-on upgrade.

Don't forget, you'll need the larger bore master cylinder and new brake lines down to the proportioning valve as well.

 

It looks like the bottom holes once drilled out line up with the bottom studs of the booster. It looks like all i need to do is drill holes above the original M/C holes. Can anyone confirm this?

 

The bottom 2 holes have tack-welded square nuts on the inside of the firewall are are used to anchor the bottom of the pedal housing to the chasis. I can't say for sure that if you drill these lower holes out, and then drill 2 new upper holes that you'll have the booster rod and clevis lined up correctly with the brake pedal.

Try it. Worst case is you'll need to get 2 new longer bolts, washers and nuts to put back in these lower holes to reanchor the housing if things don't line up.

 

I recently did this with my 1970. I used the bottom two holes and drilled new top holes, You have to drill out the bottom holes captive nuts to take the booster studs. I also removed a lot of the interior to get to the nuts, it is a pain to do but I am much happier with my cars brakes even though it should'nt make your brakes work any better it does feel like it.
Mark.......