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.

[Eric_Shea]

Sorry, I didn't see this thread.

That mechanism in the first post is for the internal adjustment of the rear calipers. They need to be adjusted so the handbrake will work properly and to help keep a high pedal. The mechanism serves two functions:

1. It has a right hand thread that allows the pistons to be adjusted in and out for venting clearance.

2. It is spring loaded so it allows the piston to operate normally via hydraulics while still being attached to the adjuster shaft.

A "Knockback" mechanism is not incorporated in the rear calipers which is why it's a good idea to check the venting clearance and adjust manually every year.

A "knockback" is the mechanism in the "Front" caliper pistons that rides on a pin. These actually work in reverse to what had been described herein as having the pads "knocked back" in. The ATE knockback mechanism actually knocks the piston "outward" to accommodate for the wear of the pads. Think of the old child's play toy with the woodpecker on a stick. Flick the tail and it shimmies down the pole. These work in reverse. There is a brass sleeve which cocks and locks on the pin inside the caliper. A small internal spring then pushes the piston outward toward the pad to help keep a high pedal.

The runout on the rotor helps set the clearance and the internal bore seal also helps pull the piston back in. The knockback mechanism, knocks the piston back "out" toward the rotor again to establish a firmer pedal with less travel.

Later (1976ish) ATE began using cup style pistons in almost all of their calipers and the knockback pin and mechanism was relegated to the history books. These later cars had booster circuits (power brakes) which kept a residual 2-3 PSI on the system at all times effectively knocking the pistons back out toward the pad/rotor.

Hope that helps.