A little help with Disc Brakes

tr23

Original poster
Member
Jan 28, 2014
22
Hello All

I hoping I can get some help understanding disc brakes a bit better.
Are the rubber boots over the caliper slide pins the force that pushes the pad off the rotor when hydraulic brake pressure is not being applied? Should those rubber boots be tested for the speed or force with which they push out the caliper pins, and therefore replaced when they get less "springy"?

Also, why do some vehicles, including some GMTs have two different caliper slide pins on the same caliper - one with 3 flats at the tip and another with a rubber sleeve? What is the purpose of the difference? To me they are not interchangeable, as the bore is slightly different between the two holes, and the action of the slides becomes restricted if your insert the pin the in the wrong hole. I found this same issue on my Ford Ranger.

Any insight anyone can offer? - Thanks in advance!
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Good question. The slide pin boots are just there to keep their grease clean. If the slide pins bind up, then the calipers don't self-center when the brakes are applied and then you get asymmetrical pad wear.

The pad retraction force comes from the deformation of the o-rings around the circumference of the pistons. This o-ring is "square-cut" so it tries to go back to its original shape more than if it was round.

I'm astonished at how many this times this question gets posted and answered incorrectly, even on Yahoo Answers. :no: :confused:

Good answer: A Different 'Angle' On Brake Pulsation: Underhood Service

View attachment 32821
 

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