Anyone know power drum brake systems?

[Jackal]

63.5 Galaxie, unsuccessfully tried to convert to dual reservoir master cylinder system and have specific questions about bore sizes between the MC and wheel cylinders. Is anyone here interested in helping me sort it out? All stock parts. Thanks!

[cattleFEeder]

Mine was done when I bought the car but the master cylinder is a Gm 1 inch or 15/16 bore.
The MC is for a 74 impala. I have 4 wheel discs now. It stopped ok with drums, front discs were a major upgrade and haven't driven it with 4 wheel disc yet. Still waiten on a drive shaft from strange engineering after a new rear end housing upgrade.

[Falcon67]

MC bore size is one of the key things.  As noted most drum/drum and manual disk/drum use a 15/16 or even 7/8 bore MC.  Since drums are self energizing, the bore can be smaller because it doesn't have to move as much fluid.  On a Disk/Drum, you'll want a slightly larger bore because of the larger piston area (stock type single piston).  The MC bore thing works like this - large bore, lower line pressure, higher/hard pedal if too large for the wheel cylinders.  Small more - higher line pressure, more travel - travel and volume is the issue to work disks depending on the design.

Also on power vs manual - your pedal ration has to change.  Manual will have a higher ratio - like 7:1 or some such - vs a power pedal.  If drums are turned right, they really should not need power assist IMHO.  I also run a race car that has been near 100 MPH and have no problem stopping the car with my manual front disks/10" rear drum setup.

[Jackal]

Thanks guys, got some info I was missing from Garrett at Mustangs Etc. and Booster Dewey at Power Brake Booster Exchange so I may have an answer but I will run it by ya'll in any case. Exactly, sounds like larger bore=shorter, firmer travel and smaller is longer and softer with more apply pressure possibly.

Had the stock power drum/drum brake system with Midland 10" Gen2 brake booster and 1" bore single res. MC. Front wheel cylinders are 1 3/32" bore and rears are 15/16" bore. I'm told this is all stock spec.

I replaced the MC with a '67+ Galaxie power drum/drum 15/16" bore w/ larger rear reservoir, (before I knew better) front wheel cylinder with 1" bore, and rear with 15/16" bore. Also completely rebuild the drums. The braking is terrible now at best and the booster valve opens enough to cause annoying rise in idle RPM.

It sounds like I actually want the equal size reservoir 1" bore 1967 Mustang MC and to swap the front wheel cylinders back to 1 3/32" bore and I SHOULD be in good shape.

[Jackal]

Even though I feel like I'm onto something, it's still bugging me that the current setup seems so bad. Hate to invest even more money w/o some confidence. Getting to where I could have bought Wilwoods all the way around.

This brake booster was also used with 15/16" bore masters, so considering that I now have a 15/16" master, have 1" front wheel cylinders which I'd think would be ideal, and slightly oversized rears at 15/16" vs. 7/8", I would think that this combo should still work just fine...

[alf1960]

   I upgraded my 64 galaxie with power drum brakes to a dual master cylinder.  I purchased a dual master cylinder for a 67 Galaxie with power drum brakes. Bolted it on and it works fine. I had to modify the lines but everything else stayed the same.

[Jackal]

That's what they say, but I have all the luck with these things.

[cattleFEeder]

http://www.autokrafters.com/p-22174-power-brake-booster-kit-1952-70-full-size-ford-and-mercury.aspx
There saying 1 inch bore for drum brakes 1 and 1/8 for disc brakes.

[Jackal]

I believe the 1" bore dual res. '67 Mustang power drum/drum MC is going to do the trick. The short, hard pedal is back and she stops. The pedal no longer goes to the floor and the idle RPM doesn't increase much at all. A re-adjustment and some 1 3/32" bore front wheel cylinders outta complete the puzzle. Thanks to all who contributed!