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Old 04-07-2008, 10:33 AM
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brake pedal ratio

Hi
on a manual brake set-up the recomended pedal ratio is 6 to 1. Anybody using 5 to 1 and how is it?
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Old 04-07-2008, 12:29 PM
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Too many variables to say. State the specifics of your system, bore sizes and type of all components.

Why do you want to go to a 5:1 ratio?

Later, mikey
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Old 04-07-2008, 12:47 PM
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I have 4 wheel drum brakes,dual MC with 1" bore. Because of how things are going together I have to go with a straight arm up trru the floor (no room for an L shaped lever it was 12" long but had to put 2 bends in it to clear the steering column ,and dont want it up higher than it is if possible
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Old 04-07-2008, 02:44 PM
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The 5:1 is usually a power boosted ratio where the 6:1 is(usually) a good manual ratio if the components are sized correctly. With 4 wheel drum brakes and a too large MC or WC bores, you might have a problem. As Mikey requested, give us some more information.

Dave W
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Old 04-07-2008, 03:00 PM
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it is manual,no power the rear wheel cys are whatever stock gm 8.25 10bolts come with and the front is a corvair IFS and I think they are stock also 10" brakes all around
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Old 04-07-2008, 04:44 PM
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Quote:
Originally Posted by yragat
it is manual,no power the rear wheel cys are whatever stock gm 8.25 10bolts come with and the front is a corvair IFS and I think they are stock also 10" brakes all around
We can help but you sure aren't giving us much to work with
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Old 04-07-2008, 04:56 PM
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What all do u need
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Old 04-07-2008, 05:33 PM
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Quote:
Originally Posted by yragat
What all do u need
wheel cylinder bore size, and brake line size also
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Old 04-07-2008, 05:55 PM
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wheel cyl are 7/8 brake lines are 3/16 ,residual valves are 10 lb and I have an adjustable proportioning valve on the rears the MC and pedal is speedway #91631926
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Old 04-07-2008, 06:53 PM
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I originally had a 5.2:1 ratio pedal with a 1" bore MC on my T, no booster, disc front, drum rear. The pedal was firm and required a lot of pressure to lock them up. I changed to a 7/8" bore MC and the pedal pressure to lock the brakes seemed like it was half of the 1" bore. If you can't do anything to improve the pedal ratio, reducing the MC bore is the next best thing followed by a power booster. Good luck to you.
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Old 04-07-2008, 07:07 PM
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I just bought this MC havent even drove the car yet still needs wired and a few other things,I really don't want to buy anotherone I'm on SS and everything is going up except my income!

and no room for power booster
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Old 04-07-2008, 09:37 PM
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Quote:
Originally Posted by yragat
I just bought this MC havent even drove the car yet still needs wired and a few other things,I really don't want to buy anotherone I'm on SS and everything is going up except my income!

and no room for power booster



Drive the car , see how it works. It may work fine for you as is..


If you find, after getting the car on the road, that the brake operation is marginal, a new master cylinder with a 15/16" or 1" bore is not that expensive. You don't need anything fancy.

I would say that you can work the pedal ratio at the bottom of the pedal, but then with what you already have done to the upper part of the pedal, , you will lose piston stroke...Not a good way to design a new system.


Later, mikey
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Old 04-08-2008, 06:07 AM
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I don't think I could do anything with the bottom part because it would make the piston rod go at an angle (it's on a slight angle now) but I could add 2" at the top wich would put me back at 6 to 1 .I think today I will c-clamp a 2" piece on and see how comfortable it would be to get at it --if it feels right then I will add a piece. What do u think?
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Old 04-08-2008, 07:25 AM
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yragat - regarding the pushrod angle.

I faced the same thing as I also modified my pedal to get a better pedal ratio. I suspect I ran in to the same issue as you are now - relocating the pushrod on the end of the pedal causes the pushrod to not be perfectly aligned with the piston stroke on the MC. I machined a piece of aluminum billet to go between the MC's mounting flange and the bracket the MC mounts to, and then drilled the holes in that to accomodate the MC mounting bolts and the pushrod. This was machined to be at an angle that matched angle the pushrod was off by. In my case, that angle was 4.2 degrees. The machined plate was 1/8" at it's thickest part. This in effect changes the mounting angle of the MC to match that of the pushrod that enters it. I found that I occasionally felt a very slight 'catch' or click in the pedal when applying the brakes until I corrected that angle. I have subsequently changed over to a smaller bore MC.

As Mike says, drive it and see how you like it. You can always make any of these changes without much effort later on.
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Old 04-08-2008, 07:41 AM
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Cucumber1949 said it all.
Good stuff.


Mikey
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