Question about drilling holes for Power Booster

[prayers1 153]

I just  got the Manual to Power Brake conversion from Mustang Steve. It was the Master Cylinder, Booster and Automatic Pedal plus all the fittings, nice set!

 

Before I go at it, I want to make sure of one thing. On his instructions he said to use a 1/2 Drill when drilling the holes on the fire wall.

The Booster studs are 3/8's. Is he saying to use a 1/2" drill or use a 1/2 bit???

[1969_Mach1 333]

I would drill to 7/16" at most and see how it fits, maybe if you have 13/32 try that first.  It's standard to drill bolt holes for common usage 1/32" larger diameter than the bolt size.  Use a step drill bit if you have one.  Some call them Unibits.  They are conical shaped with steps of incremental sizes.  They don't need a pilot hole and they cut sheet metal much easier and smoother than drill bits.

[Brian Conway 264]

Of course ask questions and use the  ' measure twice cut once ' approach but both side of these drilled holes are covered.  Booster on one side and pedal support on the other.  The pedal support may in fact mount a bit easier if the 1/2" holes have a little wiggle room for moving the booster around ?  Brian

[prayers1 153]

For those who are doing this swap-

 

Here's what Mustang Steve says-

If you use 3/8" holes, you won't be able to get the booster studs all in at one time. 7/16" will work, but if you use 1/2" bit you can be assured they will go in easily. If you dislodge a threaded insert in the process, remove that insert and replace it with a washer.  Do not overtighten the nuts.

 

It makes sense to me, all 5 studs go through the firewall at one time do not properly line up, so going a little bigger helps.  I'm gonna try 7/16 first.

 

What he means about "Do not over tighten the nuts to the Booster" is that you can collaspe the fire wall by squeezing the Booster to the firewall because the metal spacer that is mounted behind the Booster rest against the firewall which leaves a hollow 3/4' space. So you can actually pull the firewall 3/4"

[1969_Mach1 333]

Yeah, you can tighten the nuts enough to distort the pedal support and the firewall around the bolt holes.  Originally they had a fairly thick flat washer under each of the two lower studs that don't pass through the pedal support to help prevent that at those two studs.  I installed the largest O.D. grade 8 flat washers my local hardware store had under each nut including the two lower to help spread the load from the nuts over a slightly larger area.  Use lock nuts.  Originally installed were Top Lock (distorted thread) type and not Nylock nuts.

 

I don't know what threaded insert they are referring to.  Cars with original power brakes had only one threaded insert for the booster.  Looking from under the dash it would be on the extreme upper left.  It's only there to ease installation of the booster.  You can set the booster in place and easily install that one bolt from the engine compartment side to hold it in place.

 

Did you also get the foam gasket that goes between the booster and firewall?

[prayers1 153]

Yes that threaded is the one to hold the Booster in place so that you can et the others started. I will use some washers in addition to lock nuts.

 

No I haven't got the gasket for the Booster or the firewall/steering column base either. Some vendors have those items on back order. It is on my to do list tomorrow.

 

Thanks for your help!