Rear Brake Caliper Questions Options

[ljubodraz]

Firstly, many thanks to Eric Shea and the rest of you who have written threads that are helping me rebuild my rear brake calipers on my own.

I've got a few questions so far as I wait for parts:

1. What is the purpose of the mechanism within the brake pistons? Does it allow the piston to extend and retract beyond the limits of the adjustment bolt that threads into it?

2. Is there anything I should do to test that it's working properly?



3. I see that Eric Shea recommends and uses Permatex Ceramic Extreme Brake Parts Lubricant for assembly purposes. I've also seen other threads saying to only use some hard to find $$$ ATE paste. Aside from lubricating the parking brake mechanism that pushes the internal bolt, can't I (should I) simply use brake fluid to lube the pistons and seals during assembly? Unlike Eric's calipers, mine won't be sitting around too long before being installed preventing the brake fluid from absorbing water.

[Jeff Hail]

Knock Back Mechanism

Too little clearance and the pads drag.
To much clearance and you better have a whole lot of talent when the pedal goes low after repeated braking.

Rotors have run out, knuckles, spindles, split calipers also deflect under load. Without the Knock Back Mechanism you would get a nasty pulse in the pedal and other weird stuff. Worse is having a pulse which causes a low pedal and loss of modulation. Minor corrections are needed for axial misalignment of the rotor to pad face.

Piston seals can be pretty tight. Push the pedal and the pads will retract a tiny bit, if they don't again pads drag. Drag causes heat and premature wear which in brakes excessive heat is the enemy. With the parking brake its an adjustment within a passive adjustment mechanism to set the specified clearance limit (vent).

914 KBM's are pretty dated by todays standards. Now even Brembo just sticks a coil spring in the bore behind the piston. Other designs use a simple spreader type of spring.

Highly misunderstood mechanism and they do much more than most folks think.

[rgalla9146]

Knock Back Mechanism

Too little clearance and the pads drag.
To much clearance and you better have a whole lot of talent when the pedal goes low after repeated braking.

Rotors have run out, knuckles, spindles, split calipers also deflect under load. Without the Knock Back Mechanism you would get a nasty pulse in the pedal and other weird stuff. Worse is having a pulse which causes a low pedal and loss of modulation. Minor corrections are needed for axial misalignment of the rotor to pad face.

Piston seals can be pretty tight. Push the pedal and the pads will retract a tiny bit, if they don't again pads drag. Drag causes heat and premature wear which in brakes excessive heat is the enemy. With the parking brake its an adjustment within a passive adjustment mechanism to set the specified clearance limit (vent).

914 KBM's are pretty dated by todays standards. Now even Brembo just sticks a coil spring in the bore behind the piston. Other designs use a simple spreader type of spring.

Highly misunderstood mechanism and they do much more than most folks think.

Thank you for the explanation of what it does.
How does it do it ?