Does size matter? I'm building a 54 chevy 210, and have installed a Jim Meyers racing front end that uses 81 camaro disc brakes. I'm using a corvette master, and need to get new wheel cylinders for the stock rear drums. I was just going to buy originals but was put off by the price, and the need to specail order (I like being able to just buy parts over the counter). I started doing some online shopping for something else that would work, and started wondering if I'd be better off with a different bore size now. The originals are 1 1/8", would I be better off to use a different size to better match the rest of the setup or stay with 1 1/8"?
For instance, 1985 Chevy g10 vans used the same size brakes (11" X 2") and the cylinder looks like it'll fit, they're 1 1/16" bore.
Thanks for any light you can shed on this.

Drum brakes or 'foundation brakes' like the big trucks use rely on a wedge effect for braking power. So it then lies in the diameter and width of your brakes shoes to vary the stopping power- read THERMAL DISSIPATION...


But *generally* the bigger piston area at the wheel gives the greater application force. Especially discs.

Did that make any sense at all?

You have to have enuf piston push {volume} in the master to work the cylinders.

I can not explain it as well as some others here can, but.

When you push the pedal down the master pushes say 1 ounce of fluid to the rears which each side takes 1/4 of a ounce per cup {1/2 Ounce per side}

If you change that ratio to 1 Ounce to 3/4 of a ounce per side your master might not have enuf volume to make the brakes work right.

In that scenario the brakes would not apply.

If it were the other way say 1:1/8 per cup 1/4 per side might make it lock up Pre maturely.


Hope that helps



R

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I guess what I'm asking is what effect would a larger or smaller diameter bore have on my brakes. Would a slightly smaller diameter produce a noticeably weaker braking force? I know this is a complicated question since the original cylinders were matched to the original master and front drums. I think I may roll the dice and try the G10 van cylinders, unless the parts guy comes up with a better idea, or someone on here has one.

Rob, yeah, that's what I figure, I even looked into using Camaro cyl, but they're pretty small, 15/16", and I don't know if they'd work my 11" drums. I don't think Camaros used 11" drums did they?

The best thing to do is check a chiltons manual in the specifications section. In there is a brake spec chart for various cars. If you look up the 81 camaro, it will give all of the dimensions of the front piston area, rear piston area, M/C piston size and disc/drum diameter. Match that up to your current setup, and see how close you are.

That is a good place to start. I would not use 1 1/16 wheel cylinders in the back, the truck master cylinders are usually 1 1/4"...You'll run out of master cylinder volume pretty quick. I'm thinking 1" or 15/16"

If you don't have access to that manual. I can look it up tomorrow.


Another car to look at would be a full size station wagon, those used the big brakes and used the large piston GM calipers, like the 81 camaro.


Later, mikey

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This is pretty basic math. The force (in pounds) exerted by the wheel cylinder on the brake shoes is line pressure (pounds per square inch) times the area of the piston in the cylinder (square inches). More square inches (meaning a larger piston), more pounds of force. This is hydraulics 101.

The one thing to consider (as correctly pointed out above) is that the larger piston diameter requires more fluid volume for the same amount of travel at the wheel cylinder. Since the master cylinder bore doesn't change, you'll be pushing the brake pedal a little further to achieve the same braking, but with less force from your foot. Alternatively, with the same force from your foot, a greater force will be applied at the brakes when the larger wheel cylinder is used. Within reason (ie, wheel cylinder bores up to around 1 3/16"), a Vette M/C will have plenty of volume.

Thanks for the help guys, just wanted to get some opinions before I bought them. I'm just leaving to get them from NAPA, 80 impala cylinders, since they have 11x2" (like mine) brakes and use 15/16 cylinders. I think these will be better matched to my disc/drum setup. At $6.49 each apposed to the $40 each for the originals, I can afford to experiment a little.
Thanks again

what kind of rear end do you have? the '54 Chevy uses a torque tube ( so you would need factory engine/ trans ).. and the drum brake system is diffrent than any modern drum brake.

in any case, corvettes up to 1960 use the same brake parts, Chevy cars up to 1960 use the same cars

Yes, I am running the stock drive train, hence the question about matching the wheel cylinder to my other, newer components. As far as the brakes being different than any modern drum brake, I see very little difference other than the absence of a self adjuster, otherwise pretty standard stuff.
Oh, and the 80 impala cylinder fit like it was made for it, thanks again guys for your input.