Am I wrong? There has to be a basic magic number. Tell me I am nuts.
Ok, you asked for it. You're nuts... ;D
And I see you have your path laid out now, but I wanted to touch on this "old" business anyway.
Then how do vendors determine how much adjustment to allow in their angle bracket linkage? Seems that if this number were such a large unknown, we would be dealing with inches and inches of clevis adjustment to account for the millions of possibilities.
I'll leave that ultimate answer to someone who does know. I was not involved in the choosing of components, so don't know what all was specified originally. Probably just "stock" as broncnaz said.
These brackets are all at least based on the original. If not exact copies then, they're all very close. So the aftermarket didn't have to think on it too much, unless they were adding variations on the theme.
The specifications of the stock master cylinders were a known commodity too, and were pretty standard based on the design (deep or shallow) of the piston. Again, for static mounting. Not on total travel.
I would still think that "total, or excess travel" is not even in the equation. Only static adjustment. Which would naturally fall into a very narrow range I would think. The adjustments deal with pedal height and starting point only. Not maximum travel. And the master cylinder's piston starts at a known point. Fully released, or rearward in most cases.
The only time you reach maximum travel is during bleeding, or when your brakes fail. And at that point, I don't think it matters much what the total fluid flow and pedal height were. Or whether the piston bottoms out first, or the pedal does.
So given that, a stroke of 1.25" at the master is going to be 7.5" at a Bronco pedal. And that's a
LOT!
Although as said above they probably didn't matter in the end, since the full length of the stroke is likely something that nobody wants to contemplate ever being reached. If you have to factor in maximum stroke length, then you've done something wrong with the rest of the system.
If they do factor it in, it's probably "in committee" where the guys designing the pedal box and the guys designing the firewall/floor and the guys spec'ing out the brakes all hash it out over beers and dogs and figure out how, when the brakes fail catastrophically, the pedal will bottom on the floor so the master never reaches it's bottoming out point. By a small fraction of an inch maybe.
A a system such as a hydroboost, with potential damage from over-travel, would need to factor that in. Just in case someone got over-zealous during bleeding, or the system bled down from a leak and someone pushed on the pedal.
Maybe a vacuum booster too. But those could both have been taken care of in the design of the booster as well as the master. Just don't let it break until it passes more than most masters are capable of?
They're all in cahoots somehow!
The MC itself, regardless of any variable beyond the MC, should have a point of piston travel at which fluid pressure/flow peak. Any movement beyond this point will either have no additional effect or potentially a negative effect.
Well, you kind of said it there in your question "no additional" and "negative effect" is basically what you get in a hydraulic system, with regard to stroke. At least when it's all working properly, there is very little to no "additional travel" in the master.
Once you reach that point where your action is what you want it to be (aka braking sufficiently) then there really is not much more stroke going on. Sure, you're moving a bit more fluid and that's pushing the piston a tiny fraction further, but most of what you're doing is simply applying more pressure. Not more travel.
So a lot of what you feel at the pedal too is flex in different components. From the pedal arm, to the firewall, to the linkage, to the soft rubber lines. There is more moving under your foot than just the piston of the master cylinder and fluid in the lines.
Once the friction material hits the friction surface, everything else is just compression and flex.
And fluid does not compress. At least not to the point we'd measure at our level. So most of the rest is just flex.
I'd bet that the amount of additional master piston travel once you're actually braking is less than 1/8" in the master bore. Everything else is just pedal movement.
Except when it's
NOT working properly. And though I'm sure the designers wanted to factor in things for when it wasn't working properly, the key parameters were for when it
WAS working properly.
It's not the stroke then, or location of the piston that's adding additional braking force. It's the pressure the master is exerting on the fluid, and therefore the slave cylinders (calipers and wheel cylinders).
Ok, so during that time, the piston probably is moving slightly. But it's a pretty darn small amount I'd bet.
If all of that rambling didn't make sense. Welcome to the club!
I just made it up as I went a long...
Paul
