Quote:
Originally Posted by tazattitude
Once you go with a power booster, don't you also have to drill a new pushrod hole on the pedal 1" lower? I guess because of the angle change the booster adds.
At least I thought I read that someplace and did that to my truck.
|
I believe the reason for lowering the pushrod on the brake pedal arm is not due to the angle, rather it is an effort to reduce the pedal ratio.
A boosted system needs less mechanical advantage because, technically, a boosted system that maintains a non-boosted pedal ratio would/could result in a VERY power system that can be touchy - touchy as in a person would have to get used to it a bit more than a booster + boosted pedal ratio setup.
For manual brakes: 6-to-1 ratio
For power brakes: 4-to-1 ratio (i.e. push rod connection point closer to the pedal pad compared to a manual brake setup)
So, if someone were moving the location where the pushrod connects to the pedal "down" relative to the manual brakes mounting location - it would in effect reduce the pedal ratio from ~6 to ~4-5-ish.
Pedal ratio = (distance from brake pedal upper pivot to center of pedal pad) / (distance from brake pedal upper pivot to push rod connection point)
BUT, having said all this - I think MOST folks do not bother to change pedal ratio when swithing from manual to power brakes - primarily because it could screw up the geometry. Bottom line - the pushrod should be in line (approx) with the line of travel of the master cylinder piston. So, for me, I don't monkey with that and I don't try to fix pedal ratio because I don't want to monkey with (screw up) the geometry and I figues that since I'm converting to power anyway, I might as well have BIG power (i.e. boosted + manual mech advantage).
Edit - IF your new master/booster combo has a firewall mount that tilts the mc piston line of motion, then yes - in that case you might need to drill a new hole (in order to maintain correct geometry - not for pedal ratio stuff) - I'd have to rely on kit directions for that!
Edit #2 - so, for example, if installing a booster with Captain Fab's bracket (parallel to the firewall), I would not move the pivot point and I'd accept a slightly higher than desired pedal ratio. but if I were installing one of the kits that tilts the booster so it is not parallel to the firewall, then I'd want to attach the push rod to the pedal at a point that will keep the motion of the push rod in line with the line of motion of the mc piston.
My head hurts.