1993 Dodge Dakota LE, 5.2L, Auto, RWD

I have a brake related question. Specifically, the front brake calipers. The way I understand it, when brakes are applied, the caliper piston pushes the inboard pad until it reaches the rotor surface. At that time, the caliper collapses by sliding on the guide pins that draws the outboard pad toward the rotor until such time both pads are squeezing the rotor. When the brake pedal is released, the piston retracts and the pads retreat to their "home" position. I get all that.

What I don't get is on my brakes, I am not seeing how my outboard pads retreat to their "home" position. The inboard pads are secured with a clamp that fits inside the piston cavity. I get that. But there are no such clamping mechanisms on the outboard pads. They just kinda sit there with their end hooks resting on the caliper bracket ledge. What is it that returns that outboard pad so it gets out of the way of the rotor. Seems to me most outboard pads in other vehicles are clamped on to the caliper body so when the caliper retracts, it takes the pad with it. That long spring thingy that tucks under the ledge appears to exist for keeping the caliper in place (and anti-rattling) but doesn't appear to do anything for retracting the pad.

So I'm left to believe that when the brake pedal is released, only the inboard pad retreats and the rotor sorta pushes the outboard pad out of the way enuf so it doesn't interfere? If true, why do any outboard pads have clamping mechanisms on them??

Curious.

 

There are several ways calipers work depending on brand, design and purpose. If you have shoes rather than discs on the back, there are springs that pull the shoes back a little bit. Most calipers work differently. If your front calipers are clean and working properly, the piston will press against the pad. The pad will press against the rotor and you your press more, the caliper will move and pull the other pad tighter. This is why you clean the bracket and pins and lubricate them with caliper grease when you service the brakes. There is nothing to pull the pads back.

Think of walking down a stair case. You have your hand around the banister rail. Your hand is around, but not grabbing the rail. When you apply the brakes, the pads grab the rotor like your hand will grab the rail when you slip. When you release the pedal, it's like catching yourself and regaining your footing. You then release the rail but keep your hand there.

This is why when they rust a little inside or the hose collapses inside, the caliper will lock up. So in short, the caliper uses a lot of fluid compared to a wheel cylinder and the pads just sort of ride there until you hit the brakes. With no pressure, they don't drag much. When I raced back in the 1970's, I actually converted the front brakes to drums and then took the self adjusters out so the shoes didn't rub at all. It didn't make much difference but it did cut a couple of tenths of a second off our time. Keep the calipers clean and pads good and your brakes work without any drama. By riding the rotor, but not pressing, when you DO hit the brakes, they work right NOW. That can mean the difference between scaring or hitting that kid that rides out in front of you.

 

So if I understand you correctly, the caliper piston retreats such that there is no longer any pressure holding that outboard pad to the rotor. The pad does not "retreat". It just stays put but the rotor kinda pushes it out of the way, albeit infinitesimally, that allows the rotor to rotate freely. That all makes total sense to me and I can easily be sold on that concept. What doesn't make sense is why do many outboard caliper pads on other vehicles come with clips/clamps that attach to the caliper body if they are not necessary? Or are they there simply to prevent rattling noises?

 

You got it. The springs and clips hold everything together so the assembly doesn't fall apart while you're working on it. It also reduces noise. You don't know irritating until you get caliper chirp. There are all sorts of pads, shims and gooky stuff (<---fancy technical term) to stop brake chatter. Disc brakes work so much better than drums, a lot of vehicles are getting 4 wheel discs anymore.

 

OK, now that I have your ear, I have another question.

When applying the brake, the master cylinder pumps fluid to the caliper (specifically, behind the piston). The piston extends and holds as long as the hydraulic pressure is maintained. When you take your foot off the brake pedal, the fluid is allowed to "drain" from behind the caliper piston. But something has to release that pad from the rotor even if only a minuscule amount. So, the rotor could do that in a fashion similar to our above discussion AND/OR (as I understand it) there is a square cut seal around that caliper piston that sort of helps walk it back. I guess I can't clearly see how that works. What is magical about a square cut seal that stores energy in it to allow it to retract the piston? Does the seal kinda stick on the cylinder wall and "stretch" when it is pushed forward then "unstretches" as the piston pressure is released?

 

I'm just guessing here. The system is sealed so I would expect isostatic pressure when you release the brake to pull the piston back a few microns at least and that is all it really needs to be clear of the rotor.

 

That sure seems like it would be enough to me. If there is no pressure holding that piston then the simple movement of the rotor should push it back enuf...similar to the outboard discussion above. I've always heard that square cut piston seal is what retracts the piston. So something aint adding up here. I can see if a square cut seal gets rolled how it can store energy that provides a return mechanism when it unrolls. That cannot happen with a round seal. But is it enuf to actually retract the piston? Perhaps so. Like you say, only need a few microns.

 

OW OW OW! My ear! Leggo!

There is a seal, but it's just that, a seal to hold pressure. Nothing pulls the piston back, it just relaxes. The pads will be like your fingers on the hand rail I talked about earlier. Instead of solid like caliper pads, your fingers are softer, but the action would be the same. If you aren't gripping the rail your hand just slides along. (Unlike the pads, this is why you don't mess with Dragons. You're soft and crunchy and taste good with Ketchup)

 

very easy to overthink a fairly simple process ..
Hydraulic Disk brakes essentially work via the application and removal of pressure in the very basic sense.
if you wanted to get a little more in depth: the friction produced during braking heats both the disk pads, and the rotor itself .. both of these components thus expand, albeit in measurements in the thousandths of inches .. these pieces are designed to cool very quickly, so by the time you release pressure, they are also shrinking back down, creating more "retraction".
then you could get into the miniscule amount of material worn off each and every time you hit the brakes....
the clamp/hold down method on the outer pad is essentially not a factor in the application of the brakes, all that mounting really does is hold the outboard pad in place, and provide noise/vibration reduction.
if they actually were to mechanically retract, the responsiveness of your brakes would be BADLY impacted.
think about when you slide a new set of pads in... what's the first thing you have to do prior to driving again? pump the brakes up right? otherwise, you pull off, and give yourself a heart attack when you hit the pedal and nothing happens ;-)