OK,, newbie here. Reading thru this entire thread was what prompted me to "sign-up".
While there has been a ton of great info, there also has been some ongoing misconceptions about how disc brakes operate.
The amount of "movement of fluid" in order to actuate disc brakes is actually almost nothing, no matter the size of the disc pads, within normal automotive use.
The idea of having to "push a lot of fluid" to move the pads is totally false.
Unlike drums, disc brake pads already start-off in a "contact" situation,, and if the rotor run-out is within spec, the distance the pads move between relaxed and tightly clamping on the rotor is only a few thousands of an inch,, typically, the pad movement is only ~5>10 thousands .
What is happening, is not so much the movement of fluid from the MC, but rather, just a "transfer of pressure".
Although some fluid is moved, the amount in volume is miniscule.
As an example, using easy numbers; to move 4 pads, each 2" in dia, with each pad extending 8 thousands, (the calipers slide, so the movement for the piston side is doubled,) only ~ 1.6cc of fluid needs to be pushed out of the MC.
A MC with a 1in bore only has to move its piston ~1/10 of an inch to achieve this fluid motion.
With a 5>1 pedal ratio, the pedal will only move ~1/2 inch to move all of the pads into tight contact with the discs.
With disc/drum brakes almost all of the pedal travel is used-up just in extending the rear shoes before any braking effort can take place.
When I converted my '80 K20 to 4 wheel discs, total pedal travel in a "hard" stop was less than 1-1/2 inches, and part of that was just the "free travel" and mechanical clearance in the linkage.
I suspect that many issues of "long pedal travel" can be traced directly to improper bleeding.
If you look in the Chilton #28624 manual, section 9, page 6, you'll see two pics of the little tool that is used to keep the piston in the CV open,, if you don't use this device, (or something similar,) all you end-up doing is moving air bubbles back-an-forth in the rear brake lines, and you never get a 100% solid column of brake fluid without using a lot of fluid and a lot of time.
Also, pressure bleeding is absolutely the way to go if you can.
While there has been a ton of great info, there also has been some ongoing misconceptions about how disc brakes operate.
The amount of "movement of fluid" in order to actuate disc brakes is actually almost nothing, no matter the size of the disc pads, within normal automotive use.
The idea of having to "push a lot of fluid" to move the pads is totally false.
Unlike drums, disc brake pads already start-off in a "contact" situation,, and if the rotor run-out is within spec, the distance the pads move between relaxed and tightly clamping on the rotor is only a few thousands of an inch,, typically, the pad movement is only ~5>10 thousands .
What is happening, is not so much the movement of fluid from the MC, but rather, just a "transfer of pressure".
Although some fluid is moved, the amount in volume is miniscule.
As an example, using easy numbers; to move 4 pads, each 2" in dia, with each pad extending 8 thousands, (the calipers slide, so the movement for the piston side is doubled,) only ~ 1.6cc of fluid needs to be pushed out of the MC.
A MC with a 1in bore only has to move its piston ~1/10 of an inch to achieve this fluid motion.
With a 5>1 pedal ratio, the pedal will only move ~1/2 inch to move all of the pads into tight contact with the discs.
With disc/drum brakes almost all of the pedal travel is used-up just in extending the rear shoes before any braking effort can take place.
When I converted my '80 K20 to 4 wheel discs, total pedal travel in a "hard" stop was less than 1-1/2 inches, and part of that was just the "free travel" and mechanical clearance in the linkage.
I suspect that many issues of "long pedal travel" can be traced directly to improper bleeding.
If you look in the Chilton #28624 manual, section 9, page 6, you'll see two pics of the little tool that is used to keep the piston in the CV open,, if you don't use this device, (or something similar,) all you end-up doing is moving air bubbles back-an-forth in the rear brake lines, and you never get a 100% solid column of brake fluid without using a lot of fluid and a lot of time.
Also, pressure bleeding is absolutely the way to go if you can.
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