booster brake setup, im probably going to have to modify the pedal setup a little , cut it down a little to make it fit. whats the math thats supposed to work out for a power setup drum drum. i want to make sure if i cut, i still keep a good ratio. i want to shorten the bottom and the top.
I thought about this for a while too. I was having clearance issues with my bellhousing and basically had to "Z" the pedal. Is this where you need the room? This what I came up with. First,don't cut anything. Add the dark pink section. Gusset similar to the lighter pink. Cut along the dotted lines. Geometry stays exactly the same and with the gussets I have no worries about stomping the pedal. You might have to get creative about how they pass through the floor since this interferes with your toe board if you have one. I don't. I just have slots on the floor. My floor and firwall meet at 90 deg.
The pedal ratio is calculated by measuring the PERPENDICULAR distance from the LINE of action (your foot) to the pivot point. Meaning that it doesn't matter if you pedal is a pretzel in shape - the ratio ONLY KNOWS those two points - it has no idea (or effect) of how it gets there (what's in between). So if I understand your illustration correctly - then simply shortening the push rod will not change the effective ratio at all. HOWEVER if by shortening the push rod you change the pedal angle THEN you likely have changed the ratio. To REALLY figure this out it's best to draw (sketch) everything out and then put some numbers to it.
yeah my floor and fw meet at a 19 too. just seems like the only place i can mount everything...with the master accessible and have it fit right,the pedal is going to be too high, like having to lift my foot up way high to press the brake, and its going to be too far forward that its going to hit my firewall. i like your illustration, seems like that might work, altohugh not sure if im still going to be running into my firewall or not.
so if i have to make a new pedal completely, or i decide to. whats the good numbers to hit... as per this site. it tells how to calc. but not the recommended numbers for a 4 wheel drum with a booster setup.
Use those diagrams above. I use 6:1 for manual drum brakes....I've read 5:1 with a power assist. If I was running all manual disc brakes I'd go higher than 6....maybe 7:1 as unassisted disc brakes require more pedal pressure than self-energizing drums.
I run a 6:1 pedal ratio on mine. The "B" dimension is approximately 1.5". The push rod length to the master cylinder does not affect pedal ratio.
one thing to keep in mind is though 6:1 is optimum when you have really long legs sometimes less works better.
Hello all, sorry to bring back an old post but I would like a little clarification about this picture. If I were to extend the arm of the pedal (lets say away from the foot of the imaginary driver) but keeping the same height from the pivot, would dimension A stay the same or would I have to measure diagonally from the pivot out to the new face of the pedal. This is what I mean: Im probably over thinking it, because I imagine the lever/pedal ratio would stay the same no matter how far forward or behind the pivot is from the actual pedal, but I would rather be safe than sorry. I dont have much room to install an under floor pedal assembly in the project I am working on and I plan on mounting the MC quite a ways behind where the actual face of the pedal is going to be. Thanks for any help
Dimension A is dim. A regardless of the shape of the arm , however you need to consider whether or not the shape of the arm is going to interfer with you being able to use the pedal , i.e. : does the shape of the arm restrict where you place your foot , in the example you showed above it appears that your heel would hit the arm before you hit the pedal... dave
ok great thanks for the fast reply. Yeah, the pedals not going to look much like that. I just didnt know if moving the pad of the pedal further forward or behind the pivot changed the geometry, and that quick computer sketch was all I could manage haha. Thank you!
Yes you have to measure diagonally. Or rotate the drawing clockwise until the pedal is directly above the pivot, then measure the height A It's kind of hard to tell what you're doing when you draw the pedal assembly in a way that it can't be built to work. The curved part needs to have the center of the curve be the pivot point, you can't just slew the thing sideways like that. Keep in mind that the curved part of the pedal needs to go thru a small hole in the floor, as the pedal is pushed.
Ok I took a bit longer to draw out what Im talking about to clarify (and apparently test my patience with computer drawing) I am trying to avoid motor mounts that I have like big ears on the bellhousing. They connect to both sides of the frame and interfere with where I want to put this under floor brake/clutch pedal setup. They are represented by the big red box in the picture. The whole view of this is from the side, the pedal wont be moving side to side of its original location, it will be moving further away from the master cylinder, and in the broader perspective towards the front of the vehicle. As you can see from the picture I am not worried with how the pedal arm will interfere with the floor. There is not enough room in between the bellhousing and the frame rail to bring the master cylinder any further forward in the vehicle. Rather than have the brake pedal way in the middle of the floor, Im going to need to move it towards the firewall. Im wondering if I need to compensate in my measurements for the distance I am moving the pedal away from the pivot, and not just for the height of the pedal from the pivot, which will remain roughly the same as it was before changing the shape of the pedal arm. Whew... Thats what I meant to say the first time, just didnt... And drew a lazy picture. Hopefully that makes more sense what I was asking you all. But I think I understand you right that I need to measure the dotted red line I have in the picture and use that as my "Dimension A" Thanks
Yep , A is still A.... why not move the pivot point ahead of the bell mount & position the master as close as possible.... I just don't like all those bends in the pedal arm ... why have 'em if you can do without ??? dave
What you have in red is the dimension you need to worry about. Torque is force times distance from the pivot. If you were to draw a circle centered at the pivot and ending at where you push on the pedal the radius of that circle would be the length of of your "moment arm" and thus the dimension you are interested in. Hope that makes sense... Ryland
Why not leave your pedal the same, move the pivot point ahead, or move the m/c back and use a longer pushrod?
You do want to move the pedal pivot forward if you can... Also, I drew an arc showing where the pedal actually would be in this crude drawing.
Great, thank you all for the help. I will save telling about what I end up doing for one of my own posts but that answers all the questions I had about finding brake pedal ratio. Thanks again for sticking with me, crude drawings and all! Ced
I know this is and old thread, but the question is legit. Im working on a brake pedals, for an underfloor set up, and have some issues Pic 1 is just and excaple of a way to do it. Pic 2 is another way. Pic 3 is the MC im gonna use. Pic 4 is the pedals gonna use. So the question is; the part under the pivot point, if the angle of that is to steep(verical), will that lower the pedal ratio? Im running non-booster. So every inch counts. And is it a good way to set it up, when you put the lower part at a good angle, install the pedal at a good high/distance from seat and then tack, dismount and weld? Or will I have to measure it up in the rigth angle and stuff. The pedals are from a 1946 1.5 tons truck. I will convert them to push instead of pull.
In picture 2, the angle the pushrod would be on when applying the brakes would be very steep,but the real problem would be having your pivot point on the pushrod so far forward of your pedal pivot point, your foot would have to travel twice as far to move the master cylinder piston the same distance if the pushrod was more at 90 degree to the booster flange. In post #19 you would have to have a long slot in your floor to allow the pedal to travel the distance the arc would take it on. The ratio would change depending on what the angle the pushrod was to the actuator arm,90 degrees being optimum I'm thinking.It wouldn't change that much until they were at an acute angle,but your travel would be gone anyway. Could be wrong but it's the way my mind sees it.
Thank you for the reply. Post 19 has nothing with my car to do. Because I just thread jacked on his stuff, because I had almost the same issue as the OP.
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