AFAIK the handbrake never operates on disc-brakes (only on "drum" brakes or whatever they're called in english). If you got disc in all corners there will be a small, separate set of brakes to serve the handbrake. If the handbrake was operating on the hydraulic disc brakes I guess a pressure drop in the system over time would be very critical.
Rubbish. The handbrake draws a wire connected to a lever in the side of the (disc) brake. Pulling the wire causes the piston to move outwards. I'm assuming we're discussing the A4 or similar (have not bothered to check the start of this thread to see if this is the case).
Careful with that word "never". Take off a back wheel one day and have a look.
On newer Saabs and lots of other cars, the handbrake operates a variant of drum brake, even if the wheel in question is stopped by a disc brake.
/Robert ('01 A4 Avant, '99 Saab 9-3, '83 Saab 900)
Recheck your sources. Placement of sensors was not determined due to how often front or rear pads wear out.
The idea with having the sensors on the fronts is that loss of braking ability on the front axle has greater consequences than losing it on the back.
Not always. Many will tell you that they've worn out more rear pads than fronts, despite having fully-functional (i.e. not binding or rusted) sliding calipers and pistons. But yes, stuck calipers will cause dragging pads, hence wear - but this problem is easy to detect due to the outside pad wearing more quickly than the inside one, on a given brake.
I agree with that one, living in Scandinavia. I have had a stuck caliper on the rear, due to salt water seeping through the rubber bellows protecting the pin on which the caliper slides. It was sufficient to file away the rust, grease it, refit, then replace pads. I must have dislodged the bellows through careless use of my water hose . . .
The design you're thinking of (a small mechanical drum brake at the center of the disk) *is* used in BMWs, at least. However, the Audi design actually
*does* operate directly on the disks. It is a cable-actuated *mechanical* system (separate from the hydraulics) that clamps the rear pads to the disks by pushing on the pistons. Personally, I think it's kind of a stupid, overly complex and expensive design, but that's what it is.
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