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Old 12-24-2010, 06:29 AM
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Pedal Ratio Question

Can anyone tell me what the brake pedal ratio is for a 73 Vette with power brakes? It's not that easy to get a ruler back there to measure. Thanks.

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Old 12-25-2010, 09:18 AM
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Quote:
Originally Posted by biscuitville
Can anyone tell me what the brake pedal ratio is for a 73 Vette with power brakes? It's not that easy to get a ruler back there to measure. Thanks.
What are you doing to it that you need this type info ? Are you changhing brake systems or something ?



Cole
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Old 12-25-2010, 09:18 PM
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Yes, I have replaced the power brake booster and MC with a manual MC (Cardone 10-1371) since my engine didn't make much vacuum and the brakes never felt truly strong. (New calipers and they were bled.) I am guessing though, that without modifying the pedal ratio, I may still be stuck with less than optimal braking. Since I have some charts to go by, if I knew the pedal ratio then I could make a reasonable guess at whether and/or how much a smaller bore MC would help versus modifying the pedal ratio via relocating the push rod. I am trying to look this value up since getting behind the dash of my vette is really aggravating.
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Old 12-26-2010, 12:37 AM
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Unless GM quit putting the hole there in the smog years, there should already be a manual brake rod hole in the pedal, about 1-1/8" or so above the power assist rod hole. There may be a small flat sheetmetal finger bracket that triggers the brake light switch currently bolted into that manual brake rod hole that you will have to move.

All the '76 and earlier GM cars I've converted already had this hole present in the arm, Novas, Chevelles, Impalas, Vegas, heck even the '85 S-10 and '84 Monte SS had it.

I've never worked that area of a Vette, so I can't say for sure, may not be there as I don't think I have ever seen a '68-later Vette with manual brakes, they all have power vacuum resevoirs in several places underhood for various items like wiper cowl lift, headlight door lift, heater controls, etc. My stepdad has a rstomod '64 and a all original '69 Vettes, the '64 is manual with single resevoir master and 4 wheel drum brakes , the '69 is vacuum assist, but I have never looked at the pedal in the '69 so I don't know for sure it has a manaul hole. I would just expect it to be there as all other GMs I've seen including trucks have it.

GM was smart that way, no sense having to have two different pedals stocked and inventoried at the assembly plant for the same car when you could just put two holes in all of them in the stamping process.

Going to manual without changing the pedal ratio it will feel even worse than a poorly working vacuum assist will feel, you will definately want more ratio, even regardless of what bore diameter master you use.

Last edited by ericnova72; 12-26-2010 at 12:46 AM.
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Old 12-26-2010, 07:19 AM
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Quote:
Originally Posted by biscuitville
Yes, I have replaced the power brake booster and MC with a manual MC (Cardone 10-1371) since my engine didn't make much vacuum and the brakes never felt truly strong. (New calipers and they were bled.) I am guessing though, that without modifying the pedal ratio, I may still be stuck with less than optimal braking. Since I have some charts to go by, if I knew the pedal ratio then I could make a reasonable guess at whether and/or how much a smaller bore MC would help versus modifying the pedal ratio via relocating the push rod. I am trying to look this value up since getting behind the dash of my vette is really aggravating.
If you ask me the best thing for you was not to do away with the power booster and M/C, and then go to just a manual M/C JMO.
So IMHO the best way for you to make this work properly is face the fact and get under the dash and figure this thing out JMO.
And yes i have been under the dash of a corvette more then once .
But it's really not that much different then getting under any other tight spot IMHO. My personal opinion is keep what you had and make it work and i know you can.
As far as the extra hole in the pedal for a manual set-up, I cain't remember if the vette has one or not but i do know my 67 camaro has a extra hole for just that and i would be willing to bet the vette does also. JMO
So take a look and and see if it does and then your job might be alittle easier.
And like Eric said if you change these thing without changing all to match
You have to take everything into consideration here, It's the brake system that need to be done the correct way, "FOR SAFETY SAKE"
Cole

Last edited by eloc431962; 12-26-2010 at 07:26 AM.
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Old 12-26-2010, 07:32 AM
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In the assembly manual I have, there is no additional hole shown for the manual push-rod location. The manual does show both manual and power brakes for the 73 but doesn't have enough pictures to be completely helpful. However, like you mentioned, there is a second hole that is being used to hold the brake light switch striker. I believe I should be able to use that hole for the push-rod and then modify/mount the brake light switch striker in the original push-rod hole location.

Thanks for the helpful tip.
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Old 12-27-2010, 06:35 PM
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The pedal ratio for a C3 is:

5.40:1 for manual and 3.38:1 for power brakes

The brake switch bracket is used in the "other" hole (example: if power brakes the bracket mounts to the manual hole in the brake arm).
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Old 12-27-2010, 07:35 PM
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Thanks a lot for the data. Even with half of the dash apart, I am finding it difficult to get a good measurement. I took the vette out today with the brakes still set at the 3.38:1 ratio. Even with the "correct" MC (1" bore), it was definitely less than satisfactory and so I will be switching the push-rod to the upper hole. Do you have any information about where to get the correct striker for the brake light switch? I was only able to find strikers for vettes with power brakes. I have thought about how I could alter the current striker but would prefer to just buy the correct part if possible.
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Old 12-28-2010, 06:34 AM
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The only place I have found the braket is Zip's Corvettes, although others may have it. $14.00, not bad, beats making one yourself. Zip PN DB-599.

Is your present setup for manual brakes?
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Old 12-28-2010, 08:27 PM
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Thanks for passing along the part #. It wasn't clear from the website if the part was for power or manual brakes so I sent the guys at Zip an email.

To answer your question, the car had a power brake system and I am converting it to a manual. I want more space under the hood and my cam didn't give me quite enough vacuum. I am following the instructions from http://www.maliburacing.com/manualbrake_pete.htm to some degree.
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Old 12-29-2010, 04:52 AM
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Have yo removed the booster yet? That is a pain in the *** job.

You will find that the manual master cylinder is mounted in a different location that the power. Also the pedal braket is different for manual vs. power. However the power brake bracket can be drilled for the manual. Below is the two brackets, power on left (4 holes for booster) and manual on right (2 square holes at top for master cylinder mount).

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Old 12-29-2010, 04:31 PM
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Thanks for the pictures. Yes, I yanked the booster. The hardest part was reaching the 4 nuts. I have built an aluminum bracket to make up for the different mounting location and will upload some photos once I have the project completely figured out.
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