Hello,

I have a 1981 300TD turbo 617 952...402000km. I replaced the front rotors and brake pads, and noticed that the new pads are always touching the rotors, even when brakes not applied. I checked the rear brakes and that is the same. Should they always be rubbing slightly or should the piston return to a position that takes the pads off the calipers by a few mm? I'm wondering if my pistons need some brake lube or if they might be shot? A related question is how freely should the wheels spin when car is jacked up?

Thanks for any insight or help!

Rod

There's always minor contact. There's no mechanism to push the pads away from the rotor. The wheels should spin relatively freely but not like there's absolutely no pad contact.

Sixto
87 300D

Yes.....if you feel major dragging however and they are difficult to turn by hand......then there is an issue with a sticking piston or two, but they will get really hot really quick if they are.

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This is normal. You will feel the pads dragging on the disk when you jack up the wheel and turn it, however, once you are on the road the run out in the wheel bearings will push the pads back just enough after a couple of turns to pretty well eliminate the drag, until you brake again.

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'97 E 300 D

The seal in the caliper is supposed to retract the piston very slightly. There's even a spec for it: 0.01 - 0.2 mm, depending on pressure.

The OE factory caliper/piston seals depict vili-like fingers on the rubber. Newer seals are a square-cut gasket. The brake fluid pushes the piston that deforms the gasket out-of-square. Remove the pressure and the rubber pushes itself back into square, ever-so-slightly retracting the piston. In practice it probably looks like the pad is still on the rotor since the tolerances are so small.

However, if you're not careful about cleaning and lubing the sides of the pad carriers with a good brake grease, then this may not work correctly. It's also possible that that seal in the piston is nearing it's limit.

But if the rotors aren't getting hot, or your mileage isn't suffering, or your handling and braking are normal, then they're probably okay and they just look closer than you're used to.