Brake pedal ratio

[Xram]

I recently purchased a 64 Dodge 330 that was fully restored. I’m 76 and done with restorations. The car was done beautifully and I will make very few changes. One aspect of the car that I’m not happy with is the brakes. It has a four wheel disc brake conversion with manual brakes. To get it to stop the pressure on the brake pedal is very high. Reading some of the posts on this forum, I decided to check the brake pedal ratio. It turns out to be around 4:1. So, I think I should change that to around 6:1. Is that a good assumption? To do that it looks like I need a different bracket that the brake pedal hangs off of? The car was originally a 6 cylinder stick and now has an automatic. Any help would be appreciated.

 

[RemCharger]

Sounds like you need the manual brake pedal assembly.... but your car likely didn't come with power brakes?
Not sure what you have going on there

 

[Nate S]

Changing that ratio isn’t so easy. Going higher would mean connecting to the pedal arm higher and therefore placing the master cylinder higher. The way this is normally done yields the same result but instead is achieved by going to a smaller bore master cylinder.

A 6:1 pedal vs a 4:1 pedal will provide 6/4 or 1-1/2 times as much braking for the same effort. If today you have a 1.125” bore MC you would need to go to one with 2/3 the area (.918”) or the closest fraction 15/16” to have the same result.

Key to remember here is that the pedal needs to move farther either way for the same result.

 

[Geoff 2]

I take my hat off to you. 76 & running manual disc brakes. Worth a Purple heart...

Disc brakes require about 50% more line pressure than drum brakes. Where will that pressure come from? The correct fix is to have a booster fitted &/or smaller diam m/c.
The problem with arbitrarily changing pedal ratio is this: the system is designed so that when your #10 is pushing on the pedal, the line drawn from the pedal pivot in the pedal box through the p'rod bolt pivot on the pedal forms a 90* angle with the m/c prod. This ensures max force [ leg power ] is exerted on the m/c piston, Outside of 90*, the force is reduced. Just redrilling the hole in the pedal will change the 90* angle. Less than 90*, you will have more pedal travel & less braking force.

 

[Dan64]

Steve, I have the same exact thing going on with my 64' Polara. I could kick myself in the butt for not checking the ratio when i had the car stripped and dash out, would have been a 5-minute job. What I discovered was that my car for some reason or another has a very long pedal with the top hinge bolt going through a riveted bracket that sits on top of the main bracket. After looking into this problem, I haven't been able to find another 64 with the same set up as mine as all the other that I have seen bolt through the main bracket and there are two holes for power / manual . I bought an auto pedal assembly from someone stripping a 64 but have not installed it yet.

 

[65hemi]

I had a 1.xx” bore MC for my front disc conversion car and the pedal pressure was higher than expected. I changed to a 15/16” bore MC and the car stops way better.

 

[RemCharger]

A pic of the master cylinder height would help.

 

[Ron H]

I’ve posted the long story about the disk conversion hassles I encountered with my ’63 Plymouth also converting from manual to power. Part of it was the kit I obtained was incorrect for my car, though got it working fine. Your pedal arm may have two holes; upper for manual and lower for power brakes. As it ended up with mine I was able to leave the power brakes with the manual pedal ratio arrangement. Long story; but after machining a new eyebolt with light switch stop pad and making a new rod, adjusted it to do the job gaining the desired pedal travel, height, and position (these were among the problems). The eyebolt with the kit was a piece of junk. Anyway, just MO, I’d be inclined to explore installing a power brake setup to give your leg a rest.

 

[Xram]

Thanks for all the replies. Since the car was originally a 6 cyl with manual brakes and was changed to an automatic, I don’t know if the bracket that holds the brake pedal came out of a manual brake car or a power brake car. I think I’m going to explore the master cylinder and if it is bigger than 1+ inches, I’ll try a smaller one. Changing the brake pedal ratio looks to be a job I’ll try to avoid.

 

[Kern Dog]

I drilled a hole above the stock one in my '70 Charger and it did help. My system is a bit of a hodge-podge though.
1975 Dart power booster and master cylinder with 15/16" bore, 12" Cordoba front discs with 2.75" calipers, Dr Diff 10.7 rear discs with 1.5" bore calipers.
When I converted to the 5 speed, the brake pedal was changed to a manual trans type and I lost that small advantage. The car stops fine but it used to be better. I've contemplated modifying the manual trans spec pedal but have yet to do so.

 

[RemCharger]

I just stumbled upon my old power assembly from my 64, when I converted to manual..

 

[Xram]

Thanks RemCharger. My bracket looks very similar. My brake pedal arm is 17 inches long and the distance from the pivot to to the hole for the m/c shaft is around 4 1/2 inches. That gives around a 4:1 ratio. From what I’ve read a manual brake car with discs need around a 6:1 ratio. I think I’ll look at the m/c first.

 

[Dan64]

I just stumbled upon my old power assembly from my 64, when I converted to manual..View attachment 1266254View attachment 1266255View attachment 1266256

That's the same bracket that I have in my 64' currently and need to change out to the manual style one. You mentioned that the master cylinder uses different installed heights between the two different styles?. Do you have a picture of yours installed, it might help clear up some things for me ( and others reading this) thanks @RemCharger

 

[Xram]

That's the same bracket that I have in my 64' currently and need to change out to the manual style one. You mentioned that the master cylinder uses different installed heights between the two different styles?. Do you have a picture of yours installed, it might help clear up some things for me ( and others reading this) thanks RemCharger

 

[Xram]

This is a picture of mine currently.