Basic disk brake question
 

This question came to me while I was putting new brake pads on - I know what pushes the pads against the rotor, but what pulls them away?

I should probably know this, but . . . :rolleyes: :confused:

By the way, thanks to all the help on this forum concerning pad replacement, I was able to do it in about 5 minutes per wheel. I really appreciate this place! :) :cool:

I've said this before
 

and I'll say it again. The SVX is the easiest car to replace pads on that I've ever owned!

Todd

Oh, sorry, forgot about your question Dick. Nothing really retracts the pads. The release of line pressure merely allows them to slightly move away from the rotors with the movement of the caliper.

The seal inside the caliper is 'square-cut', in other words its cross section isn't round like a normal 'o'-ring but square-faced. When hydraulic pressure is applied the piston is forced outward and the drag of the piston against this square-cut 'o'-ring causes it tip/slant/follow along (if the piston was traveling to the left, below the following lines, the 'o'-ring would move from this: |_| to this: /_/ ) When the hydraulic pressure is relieved the 'o'-ring relaxes to its natural state and retracts the piston to its original position. Now, you can imagine that there isn't much retraction force working here, so any build-up of gunk, etc. inside the caliper inhibits the amount of retraction. That's why rebuilding the calipers at each brake job, and/or flushing the brake fluid every couple years is recommended. (The gunk is comprised of moisture mixing with the brake fluid, deteriorating brake fluid and rubber parts and from sand casting residue still being released into the system from the master cylinder and calipers.)

That takes care of the inner pad on a single piston caliper. The outside pad retracts as a result of the caliper's mounting hardware or it just gets knocked back a bit by the rotor's deflection on its bearings during turns, etc.

Thanks, guys!

Have a Happy Thanksgiving.

Ok, so what do I add to my parts order to get everything necessary done? I'm guessing new dust seals, pins & guides, and this seal? I also ordered new shoes for the emergengy brakes, but are there any other small parts that I sould replace while I'm in there? I'd hate to skimp on a $0.50 part and have to redo the labor again later.

FYI: I just placed an order for the following items for a major overhaul I'm planning to do very soon. Suspension and tranny work is on the back burner while I start looking for a backup SVX. Does anyone have any suggestions as to other minor items of interest for a 180K mile overhaul?

timing belt
water pump
radiator hoses
cam & crank seals
bearings & o-rings for PS pump
and a few assorted clips, seals, clamps, bolts, etc...

KuoH

Oil pump seal (o-ring)
O2 sensors (?)
Radiator cap
Thermostat
Brake fluid flush

Sorry, I didn't mention all the small parts that were ordered. Pump o-ring, thermostat, and flush were ordered or planned. O2 sensors are pushed back for now as I'm not experiencing any driveability issues or CE indicators. I didn't think of the radiator cap needing replacement, but I'll check into it. Thanks.

KuoH

The last little bit that ensures that the pads are away from the disk, is the boundary layer of air that runs with the disk, it forces itself between the two, to seperate them.

This is the same layer of air that causes brake squeal, when it is trapped between the two, when the brake is applied.

Harvey. ;)

so in theory, slotted rotors (which allow that air to escape from underneath the pad) will eliminate squeal?

-adam

That's the theory Adam, but you still need the spring shims behind the pads to be sure.
Harvey.;)