Rear Brake Pad Dimple Thingy

[Martin350]

Does anyone here know what the small round 'dimple' thing on the back of some rear brake pads is actually for?
It locates into the caliper piston, of course, but why?

In this photo, the top pads are after market without the 'dimple' and the pads at the bottom are o.e. with the 'dimple'.



I'm guessing it can't be too important that it isn't there but I'm curious now as to what the dimple does.

Edited by Martin350 on Thursday 2nd March 15:53

[stevieturbo]

Usually locates into the piston on a caliper with a wind back piston for the handbrake.

[Martin350]

Yes, but why?

[finlo]

Because without it the piston would just rotate and not extend as the pad wears down.

[stevieturbo]

Martin350 said:

Yes, but why?

To prevent the piston rotating and perhaps affecting handbrake or indeed hydraulic brake operation because of it.

[227bhp]

Dimples are inverted or concave.

[S0 What]

As said it prevents the piston from rotating and backing off the handbrake mech, see the pic below, the piston "might" turn and screw itself back down the thread of the parking brake thrust screw, result is usually a slightly long pedal that comes up if you quickly lift off and re apply the brakes/steering wandering under heavy braking/high handbrake lever/crapper than usuall handbrake effort, pretty much the same as a drum with poorly adjusted shoes.

[Dave Brand]

Martin350 said:

I'm guessing it can't be too important that it isn't there but I'm curious now as to what the dimple does.

No, what it means is that the aftermarket manufacturer has missed a feature which the OE manufacturer considered necessary.

By the way, the correct term is spigot!

[Mr2Mike]

Dave Brand said:

No, what it means is that the aftermarket manufacturer has missed a feature which the OE manufacturer considered necessary.

This is most definitely an important feature for pads fitted to handbrake calipers. The entire design of the caliper depends on the piston not rotating during normal use, so those pads should be going straight back to whoever sold them to the OP.

[Martin350]

Dave Brand said:

No, what it means is that the aftermarket manufacturer has missed a feature which the OE manufacturer considered necessary.

By the way, the correct term is spigot!

Ah, I did wonder what the correct term for it was, thanks!

[Martin350]

And thanks to all who have replied.

They aren't my pads but a friend of mine's and he asked me what I thought.
I had my suspicions and they seem to be confirmed.

Thanks!