Pedal Ratio Question

[Gratefuldiver]

I just finished up my 4 wheel disc set up and had a question about pedal ratio. I measured from the pivot point to the hole for the booster rod 4.5 and pivot point to bottom of pedal 13. That's not the 6.1 ratio I hear I am looking for. This is a stock pedal setup in my 72 GTO so the pedal has two holes. The sec hole (unused) is 2-2.5 from pivot point. That would get me a lot closer to the 6.1 ratio. The brakes work and feel great but if I can make them better I'm all for it. Should I move the booster rod to the hole closer to the pivot point?

I'd also love to hear what type of pressure I'm making with this set up. My set up is as follows

1" bore master
9" single booster
Vac pump 15lb on 22lb off
Baer track 4 calipers with 4.0?? Piston volume front
13" rotors front
Wilwood D154 calipers with 1.9? Piston Volume rear
11.125" rotors rear
Front pads are what Baer sent with kit
Rear pads are Wilwood series 10
Using stock portioning valve that's had the spring and plunger removed
Pedal ration info above.

What other info do I need to figure it out?

[a67]

Since you are running a booster, should be using the lower hole (further from pivot) in the pedal. The upper hole is used for manual brakes.

A single 9" booster is not going to provide much assist. A dual 9" would be much better.

Bob.

[Gratefuldiver]

I've been told that before about the booster. At some point I'd like to dump the booster and rattle monster vac pump and go with a hydro boost.

[Gratefuldiver]

I guess I'll put out a request to Ron to crunch done numbers for me with my set up. Just curious how my set up rates. Thanks

[Ron Sutton]

I guess I'll put out a request to Ron to crunch done numbers for me with my set up. Just curious how my set up rates. Thanks

In manual systems, which I have a lifetime of experience, the math always matches reality. I haven't nailed down how to be accurate when power boosters are involved. I know the math ... but the math's answers don't seem to match reality.

Reach out to Tobin, because he has a very good handle on this.

:cheers:

[a67]

I guess I'll put out a request to Ron to crunch done numbers for me with my set up. Just curious how my set up rates. Thanks

In the sticky above I posted an Excel SS that will provide the numbers for you. Just need to plug in the specifics of the system and the braking force is calculated and shown.

Bob.

[MCB Matt]

With the correct booster it will bolt up at an angle to the firewall, this was done for clearance under the booster. The rod comes in at a downward angle so it must go in the lower hole in the pedal or it will kill the booster as it will bind every time you push the pedal.

If you don't have at least 15" of vacuum steady at idle you don't have enough for a booster.

No matter what size the booster is, they all require the same amount of vacuum. Even if you run a canister and pump it will be just enough for 2-3 pedal applications before the pump can't keep up!

Hydroboost is the answer to your issues without a doubt... It will put out close to 2x the assist the 9" booster is now, actually, if you have vacuum issues it will put out several times more!

If the pedal is "hard" and it feels like no matter how hard you push you could never lock the brakes its for sure a vacuum issue.

Let me know if i can help you out with the hydroboost, we carry Hydratech, they have 3 levels of "prep" (they all function the same, its just how much time they spend smoothing the casting, painting it ect) and the hardware that is used.

I ran an ad awhile back in the vendor section here on the board, you can see the different levels of prep there.

Matt

[cdrod]

In the sticky above I posted an Excel SS that will provide the numbers for you. Just need to plug in the specifics of the system and the braking force is calculated and shown.

Bob.

Bob:
how do I get to the "sticky"? Your brake force spreadsheet would be very helpful to me as I'm trying to calculate MC size and booster size to fit C4 vette brakes on a '72 442 convertible. I've calculated the MC and line pressures as well as the caliper force, just having a bit of difficulty calculating the brake torque at the rotors. Thanks!
Rodney

[a67]

A sticky thread is one that is always at the top of the forum. It is stuck there so that it doesn't fall down the list due to no new posts.

It is post # 140 in this thread:

https://www.pro-touring.com/threads/104584-Brake-sizing-and-selection-tutorial-featuring-Ron-Sutton-and-Tobin-of-KORE3/page7

Bob.