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06-02-2009
Machine bled doesn't mean anything, air still rises to the top. As for the total piston volume being larger, again, numbers? Everything I have seen puts them very, very close to the same.Originally Posted by Sabrewings
Edit for SC Drew's numbers:
Stock caliper 2.5" 1.25x1.25x3.1415 = 4.908 sq/in.
F-body 1.77" .885x.885x3.1415 = 2.460 x 2 = 4.92 sq/in
So you might be right, they're larger by 0.2%
06-02-2009
With the machine the fluid is forced through the lines faster than the air can move, so it has to come out. The bleeder is closed before the connection is broken, so its impossible for air to be introduced.
Doing the math... If a F-body piston is 1.769" then that's 2.46 sq inches per piston. Total per caliper is 4.92 sq inches.
On our stock calipers he said it measures 2.5". That's 4.91 sq inches per caliper. Hmmm... 1/100th of a square inch is a pretty small difference. I'm not sure what to tell you. All I know is that cars with F-body pistons which are vacuum bled still feel softer.
I'm also going to try and independently verify those bore measurements.
06-02-2009
The air is already in the caliper and lines from the replacement, it's not a problem of it being introduced during bleeding. If the air is higher than the bleeder screw, how do you get it out?
As I said, that's my current theory, I have yet to put it to the test. It'll happen in the next couple of months.
06-02-2009
I see what you're saying about it now. You're talking about it being in the piston. But, if you install them on the proper side, the bleeder screw will be at the top of the caliper. The only place for it to hide would be in the line which the vacuum bleeding would take care of. To install them properly you have to swap sides from what they would've been on the f-body car.
And I verified the bore measurements. They're correct.
06-02-2009
On the f-bodies, they are completely on the side of the rotor, so the bleeder is pointing straight up. On our knuckle, though, they're at an angle, and the bleeders are also at a slight angle, so they're no longer at the highest point. There's a small area above the bleeder now where air could hide. As I said, it's a theory, we'll see.
06-02-2009
you dont measure volume for hydraulic force, you measure piston bore area. volume has nothing to do with the force being applied to the piston. 3.5 inches vs. 2.5 inches stock, keeping the stock master cylinder bore will net you a higher hydraulic force at a longer pedal throw.
The end.
06-02-2009
also, you can do RFI to bleed the brakes if worse comes to worse, other then that the person working on the car is just not properly trained.
06-02-2009
Um, right... so diameter is now equal to area?
06-02-2009
We're not, we're calculating piston area, which is Pi*r^2. You're just looking at the diameter of the piston.
And guess what, area is related to volume. Area * height = volume.
06-02-2009
youre right, doesnt make sense at first i guess but the area is pretty close. depth of piston has nothing to do with it though. like i originally said, 2 pistons is better then one and they are lighter than the stockers, so for my $30 invested, damn good deal.
06-02-2009
on another note, if this is true i have no idea why people were complaining about a mushy pedal and someone said that was b/c of the piston bore size differences, but if they are that close, that couldnt be the cause. this actually makes me happier b/c when i install mine, i wont have to worry about the pedal throw being larger.
06-02-2009
But volume does affect what you call pedal throw. That's what can result in the softer pedal feel.
I work with enough hydraulics troops and their systems to know their concepts very well. My dad works in hydraulics too.
06-02-2009
I do see what he's saying, he's saying that the total volume of the piston itself doesn't matter, and he's right. One of the pistons could be .5" long and the other 3" long, so the total volume would be different, but it wouldn't affect the braking. The fluid volume needed to move the piston a specific distance does matter, but that is directly related to the area of the bore, not the total volume.But volume does affect what you call pedal throw. That's what can result in the softer pedal feel.
I work with enough hydraulics troops and their systems to know their concepts very well. My dad works in hydraulics too.
06-02-2009
but how do you figure, in a brake system application, once you pump up the brakes and they contact the pads, they only back off ever so slightly, thanks to the square cut piston seals which act as self adjusters and return springs. I could see how that would be the case with other hydraulic systems lets say, in an excavator application where you are constantly moving the piston back and forth through its entire range.
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