The first is the type that you retract by just pushing it back into the caliper’s bore, no rotation required. The second is the type that you have to screw it back into the bore, rotation is required. Brings to mind a couple of questions:
What are the advantages & disadvantages of each type? (For example, one disadvantage of the second type is you need to buy or devise a special tool to screw it back in.)
Since you have to screw the second type back in to retract them, do they also rotate as they move out when you press on the brake pedal?
Thanks. If I’m understanding correctly, with the screw in type, you could actually push them back a little w/no piston rotation needed. But only to the point where the screw makes contact with the piston. After that you can’t push them back any more, and the only way to retract them further is to rotate the piston, which turns the screw back into the parking brake mechanism. (since it is locked to the pad with those two protruding pins)
The screw doesn’t let the piston retract more that a millimeter or so. If you want to change pads, you need it to go allmost all the way in. Not happening without a tool to screw the piston in.
Informative comments above. I think I’m closing in on an answer to all of the questions posed.
Please note any corrections/clarifications needed.
What are the advantages & disadvantages of each type?
Advantage of type 2, screw-type, : Allows the brake pad to double-duty as the rear parking brake. No need for separate parking brake shoes and hat-shaped rotor.
Disadvantages of type 2, screw-type: (1) Requires a special tool to retract piston; (2) Retraction procedure, as piston rotation required, could put add’l wear on piston’s o-ring seal.
With type-2 (screw-type), do the pistons rotate as they move out when you press on the brake pedal? I believe the answer is “no”, no piston rotation when you step on or release the brake pedal. The piston only rotates when adjusting the parking brake, or when retracting the pistons to install new pads.
Good progress, but yet another question comes to mind. With type-2 (screw type), do the parking brakes need to be manually adjusted from time to time (to compensate for pad wear), or is that done automatically somehow?
The only place the screw type is used is for parking brakes. Yes it does eliminate the small drum brake inside the rotor but they are not as effective as the drum, tend to corrode and jam and turning the piston can damage the seals when rotated. They require no manual adjustment because the screw mechanism is designed to adjust for pad wear and the pistons do not rotate in normal use.
And as a side note… caliper pistons do not use O rings to seal. They use square section seals because they and the grooves are designed to pull the pads back when the brake is not applied to reduce drag for better fuel economy.
You suggested consulting an internet website above, so I’m a little confused what your intention is. I’m not dissing Google, plenty of good info there. But if Google is the preferred source for car repair and maintenance info, then it follows there’s no need for this website. Is that what you are suggesting?
I’m suggesting that for information about how brake calipers work, something like an encyclopedia would be more likely to provide accurate answers, as opposed to a forum where you’re going to get information from anonymous sources, many of which may not be all that well-informed.
No, b/c while it is true the posters here are anonymous, the vast majority of folks posting here seem very well informed. And they are able to address the specific questions posed. Google probably has the info, no dispute, but I’d have to wade through 20 minutes of u-tube vdos to find it.
BTW, still awaiting the answer to the final question, do the pad-based parking brake adjusters self-adjust with use, presumably each time applying the parking brake hand-lever? Or do they require occasional manual adjustment?
OK, didn’t notice that comment, thanks. I may have read Mustang’s post before the edit. Other than how the automatic parking brake adjustment actually works, by applying the handle or otherwise, all questions are now answered. Good thread.
The old lever actuated parking brake calipers have a ratchet mechanism inside for self-adjustment.
Modern motor actuated calipers are self-adjusting with motor position.
Below are the parts inside a brake caliper.
Starting from the right: bearing plate, jack screw, inner piston and caliper piston.
Interesting. I didn’t realize some of the new caliper & pad based parking brake systems are applied by the driver turning on an electrical switch which powers up an electric motor which screws the piston toward the disc. I can see how that could self-adjust by itself.
I’m not entirely clear however how the self adjustment works for the versions which are applied by the driver pulling on a lever. Do you mean the self adjusting mechanism is part of the lever mechanism? For comparison, my truck self adjusts by me applying the hydraulic brake (via the pedal) while the truck is backing up. The self adjuster is inside the drum. My Corolla’s parking brake self adjusts by me pulling on the parking brake lever, no hydraulic involvement, but the self adjuster is still inside the brake drum.
