Technical Geometry changed with offset master push Rod.

I couldn't find anywhere if using a offset pushrod from pedal to master cylinder would change the pedal ratio? I'm trying to increase the ratio and it seems to me an easy way out would be to offset the pusher.

Also is there a golden rule to the minimum spacing between the pedal pivot to the lower pushrod hole?

For instance: I was 2" from centerline of the pivot to centerline of pushrod mounting hole.

I brought the hole up 1" then offset the pushrod 1" back down. Did I gain anything?


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In your example you increased the pedal ratio by shortening the pedal pivot to pushrod mount.

Don't really want to think or try to comment on having a cranked pushrod in something as critical as the braking system! Don't recall ever having heard or seeing that done. Did I hear bellcrank?

Chris

 

Yes, I increased the ratio by bringing the pushrod up one inch that was my intension. Now the pushrod is not horizontal to the master cylinder bore, it's pointing down. To get it pointing parallels to the bore again I need to bring it back down to where it was originally.

Bob Drake sells a offset pusher but I can make one quicker and a hell of a lot cheaper on my own.

I'm not sure where cranked or bellcrank came into the subject or I don't know what they are pertaining to the braking system.


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An offset pusher will not affect ratio but I dont think I would run one on a brake system.

 

Any way to move the pivot point down?

 

My '68 type Novas used higher/lower holes in brake pedal to change ratio between power and non-power brake cars. The rig on those included a little tab added in with power to keep the brakelight switch happy. If that's what you are asking about, the change did angle the pushrod a small amount since the master cylinder remained in the same location while the pedal end of the pushrod moved about an inch.

 

The pivot is part of the master mounting bracket that is welded to the frame. I would be best off making a adapter plate and drop the master cylinder down a few inches.


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See picture of offset pushrod


http://dazecars.com/dazed/ofset.jpg

I moved the mounting hole up on the pedal and if I used this offset to get the pushrod back down where it was did I increase the ratio. Do I measure pedal ratio from mounting hole to pivot point or from center line of the pushrod?



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I would not put that cobbled together part on any brake system. It would be a billion times better to just have the rod make a straight shot to the master like intended, more work but far safer.

 

I wouldn't use this


But I'd use an offset rod. This design but make the tab as you needed it.

 

A bell crank.
Seems elaborate so why ??
Because it's better and Way better.



O

 

Why not change the bore of the master cylinder.

 

On my Model A , I moved the rod hole up on the pedal, to increase the pedal ratio. I also moved the master cylinder up so the rod was straight and level.

It improved braking significantly.

Phil

 

When you move the pivot up it may be easier to push, but you increase the distance the pedal has to travel to get the same amount of braking.

(Just imagine the pivot 1" from the top vs 1" from the pedal pad.)


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With a bell crank of course you can change things by moving the bell crank pivot.
...But not sure you then gain anything without moving the master cylinder or your pedal arm pivot.


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I Z'ed the push rod on several of my model A builds and never had a problem.. The rod was still straight going into the master cylinder and onto the pedal, just a spacer with a rod welded on top and a rod welded on the bottom.. It didn't change the ratio , however...

 

I did this as well on my F-1 (about 1" or less ? and no problems either after 24 years on the road)

But if you change bore size do research first. It may not do what you think.

http://www.onallcylinders.com/2013/10/29/video-master-cylinder-bore-size-affects-braking/


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How about you have a friend with a mill shave a thin wedge to place between the master and it's mount? Enough to point the master bore straight at the pedal. Could just maybe be one degree, and sandwich it at the mounting point. Wouldn't have to be more than 1/8" thick, probably wouldn't even require rebent brake lines.

 

I'm using a small bore now 7/8 or 15/16 it's under an inch.


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I was thinking like alchemy, angle the master cylinder with a tapered shim!

 

Not sure if I want to take it off level due to loss of fluid capacity.


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I'm thinking along the same lines as you. Z-ing the pushrod. The z won't do anything for the ratio but moving it up where I have it now will.

Thanks pal.


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That shim idea, good thinking! ...shoulda thought of that myself!!!


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October Car Craft has an article on a bell crank type arrangement
similar to those pictured. Page 50 in the 10/17 issue.

Nick

 

Did you move both up the same amount?


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Yes. Same geometry, but better manual brake leverage.