'63 Master Cylinder Pedal Effort - 7/8" Single vs. 1" Dual

[Norm B.]

Norm

[Kent S.]

Re: '63 Master Cylinder Pedal Effort - 7/8" Single vs. 1" Dual

Many years ago I installed a dual master cylinder on my '63. It had the 7/8" bore so no change to pedal effort. If I remember (and can't find receipts) it was off an early ('63 - '65) Chevy II. I've since gone back to the stock configuration in anticipation of judging and no sign of the old mc on the shelves.

[John D.]

Re: '63 Master Cylinder Pedal Effort - 7/8" Single vs. 1" Dual

Years ago in a 63 Couple I owned with a 340 HP and FI unit on it I went to the local auto store (NAPA) and bought a new master cylinder with 1" bore. Now the car had metallic brakes. The 1" bore cylinder improved the braking on the car even though others told me it would not.
John

[Jim L.]

Re: '63 Master Cylinder Pedal Effort - 7/8" Single vs. 1" Dual

Norm

The 1" MC will require almost 31% greater pedal effort compared to the 7/8" MC. That's enough to notice. Only you can decide the level of inconvenience that will cause.

[Norm B.]

Re: '63 Master Cylinder Pedal Effort - 7/8" Single vs. 1" Dual

The 1" MC will require almost 31% greater pedal effort compared to the 7/8" MC. That's enough to notice. Only you can decide the level of inconvenience that will cause.

Wow, 31% is quite a lot. I was guessing 10 to 15% maybe but what do I know? Now I am having second thoughts about doing the conversion to dual. I don't want every red light or stop sign to be an adventure.

[Duke W.]

Re: '63 Master Cylinder Pedal Effort - 7/8" Single vs. 1" Dual

Pedal force = line pressure x area/pedal lever ratio that I recall is 4.54:1

The ratio of areas between the two diameters is 1**2/0.875**2 = 1/0.7656 = 1.31 like Jim said. For any given line pressure, pedal force will be about 31 percent greater. The brakes will probably lock up at about 800 psi line pressure, so that's 800 x pi x .7656/4/4.54 = 106 pounds. So with a 1" cylinder pedal force for for 800 psi line pressure would be about 139 pounds!

Given that most of use have been "spoiled" by power brakes for at least four decades that probably take no more than 50 pounds for lockup or ABS actuation, stick with the 7/8" cylinder and even consider adding a vacuum booster.

With proper maintenance, single circuit master cylinders rarely fail. That maintenance is periodic fluid changes. If you use DOT 5, silicone, it's probably only necessary every 10-15 years, if at all. With conventional DOT 4 or 5 every one to five years is about right. I'd recommend a change at one year, then after another two, and if the car is kept inside and rarely sees rain or condensing humidity, every five years after the first couple of system flushes is probably okay.

Duke

[Norm B.]

Re: '63 Master Cylinder Pedal Effort - 7/8" Single vs. 1" Dual

Thank you for that clear explanation Duke, I was wondering how the calculation is done. Since I installed brand new lines in the original '63 configuration already I think I am going back to Plan A and sticking with the single 7/8" master cylinder. I can always convert to dual later if for some reason I want to because that can be done with the body on. As for a vacuum booster it has sort of been in the back of my mind if I stayed with the single MC but I will have to research that a bit and see how involved it will be.

[Dan B.]

Re: '63 Master Cylinder Pedal Effort - 7/8" Single vs. 1" Dual

Consider having your original master cylinder SS sleeved for long term reliability if you are keeping it. I did mine over 10 years ago and have not had to touch it since.

Golf is for those who can't play hockey.
I agree, still play men's league twice a week

[Frank D.]

Re: '63 Master Cylinder Pedal Effort - 7/8" Single vs. 1" Dual

With proper maintenance, single circuit master cylinders rarely fail. That maintenance is periodic fluid changes. If you use DOT 5, silicone, it's probably only necessary every 10-15 years, if at all. With conventional DOT 4 or 5 every one to five years is about right. I'd recommend a change at one year, then after another two, and if the car is kept inside and rarely sees rain or condensing humidity, every five years after the first couple of system flushes is probably okay.

Duke

Absolutely, my 63 drum brakes saved my life in 2016 and single master cylinder failures are rare as can be on properly maintained cars that are driven as a hobby especially. I added an original power brake setup to my car and for the difference in "felt" braking, the expense and trouble prob wasn't worth it. I do recommend a different brake clevis (McMaster's sells it) to get the brake pedal fully depressed height raised; it eliminates those heart-wrenching stops where the pedal seems to go down forever with little braking. This clevis raises the pedal height off the floor 2"-3" when fully depressed.

[Norm B.]

Re: '63 Master Cylinder Pedal Effort - 7/8" Single vs. 1" Dual

Thanks for your comments everyone, it really helped me decide which way I wanted to go with this. Yesterday I dropped my master cylinder off at John Stuart Power Brake which is only 20 minutes from home. They estimate about 1 1/2 to 2 week turnaround to completely rebuild and re-sleeve it. Not exactly cheap but worth the peace of mind in the long run.

Norm

[Richard G.]

Re: '63 Master Cylinder Pedal Effort - 7/8" Single vs. 1" Dual

One has to consider billions of miles have been driven with single master cylinder set ups.
The dual maybe safer but if you consider what Duke said "With proper maintenance, single circuit master cylinders rarely fail."
Was the dual system invented as for a replacement of unmaintained systems?
Only once in my life I wished I had a dual system. That was four wheeling in a 66 Ford truck. At the top of the hill, I found I had no brakes. A branch had torn my left rear brake line. I came off the hill in low range. Hardly a situation a typical Corvette would ever see.

Per Frank's comment "those heart-wrenching stops where the pedal seems to go down forever." I know the feeling.
When I first got my 63 back on the road it was that way. Pretty scary in fact. I traced it down to the lubricant I used on the adjusters.
In hind sight I should have known better. I used the lithium grease on the adjusters. The lubricant that is typically used on the windows channels.
With just the smallest amount of heat it turned into Loctite!
Note, I had replaced everything else but the screw adjusters and pads, which were, and still are, the original metallic ones.
I ended up pulling the brakes back apart and cleaning the grease off and lubing the adjusters with antiseze.
The grease did come off just like Loctite, with a powered wire brush.
I believe the screw adjusters are installed dry from the factory. (Should have been my first clue)
The result was I now have a tight pedal that invokes a sense of security as the pedal never goes more than half the way down.

Per Duke's comment I will change out the brake fluid this year on both the Corvettes.

Rick