Pedal ratios

[C15_Sierra]

My truck has manual brakes, and was a 3spd manual truck from the factory. When the automatic was swapped in, the PO removed the clutch pedal, but kept the small brake pedal in, instead of swapping a bigger auto pedal in. Now I know why.

This week, I snagged the correct brake pedal from an '86 K20 that my buddy was junking, went to install it today before I put in the new steering column. When I got the old pedal off, I noticed there were different pedal ratios. I was curious if there were different pedal ratios for power/manual brakes, now I know what they are.

The manual pedal has a ratio of ~5.82:1, the auto pedal has a ratio of 4.57:1. This gives me about 21.5% less force on the MC when I press the pedal. Figured I might as well install the pedal now, work with the decreased pedal ratio until I get around to installing the vacuum booster setup I have

BUT

When I went to install it, there wasn't enough travel in rod to line up with the pin on the auto pedal, and there's no hole drilled for manual brakes like in the manual pedal. So looks like I'm gonna have to do the booster conversion now

I'm was just posting 'cause I couldn't find any info on it before, now I know and sharing so that others in a similar situation can know

Obligatory pics...auto pedal on top, manual on bottom


Quick calcs...