My nearside front brake seems to be dragging, producing a hissing noise as I drive along. With the wheel jacked up, it's much harder to turn than the other side. Over the weekend I whipped the pads off and checked the disk. There's between 2mm and 3mm of pad left and the disks aren't badly scored (or too thin). I checked for stones in the pads, but there were none. With the calliper off, the disk spins freely without noise, but when replaced I get the hissing again. The little v-springs on the pads seemed to be working - forcing the pads apart and away from the disk, but with the caliper in place they still touched. Any ideas on what it could be? (6/01)
Insufficiently lubed sliding pins. (6/01)
Do you have standard wheels fitted? I once saw a golf which had audi alloys fitted, when the brakes wore, the calipers started grinding the inside of the alloy... (6/01)
Yeah, it did it with 14" Mazda Stealth alloys, and now with the mk2 1.8iS alloys. Having read some more stuff on the 'net, I'm starting to suspect the piston. Does anyone know if it supposed to retract a little itself when the brake has been released, or does it rely on those v-shaped springs to push the pads clear of the disc? My piston looks a bit rusty, both on the rim (where it contacts the pad shim) and inside. Is this normal? (6/01)
The springs do nothing really - a lot of cars (inc mine) don't have them. The piston does retract fractionally with disc runout and general lack of fluid pressure when not braking. (6/01)

Does anyone know if it supposed to retract a little itself when the brake has been released?

Yes, the piston should withdraw a fraction when you take your foot off the pedal. A common problem, usually cured by a good clean-up and a new set of seals. Unashamed plug........ We do sell them, see: http://www.mx5parts.co.uk/pages/calipers.htm (6/01)

HI, you say the wheel is harder to turn when jacked up? If so I feel it is possible the pistons sticking in the caliper. They will do this if they get mucky, it is a simple job, although it can be time consuming to remove the pistons, clean them, clean all seals, (replace if needed) and clean the grooves where the seals fit. CLEAN everything. If you are not carefull it can cause the pad to stick hard against the disc and damage it in a very short time. Been there, done that. (6/01)

My piston looks a bit rusty, both on the rim (where it contacts the pad shim) and inside. Is this normal?

No, it can be cleaned with wet/dry 1000 grade if not too bad (6/01)

Try taking out the pads and Chrome slides, clean behind the slides to free off pads (6/01)
The pad wear indicator. (It's usually more of a rattle, but perhaps you're just in the early stages.) Change the pads! I suppose the piston could be seized - is it getting hot? I'd change the pads anyway - if you have trouble pushing the piston back, that would indicate a piston problem, but if you can move it, it might cure the problem if there is one. (6/01)
I think I've solved the problem. When turning the wheels manually, they now spin for almost a complete revolution after I remove my hand, and the hissing has gone too. They used to stop virtually immediately. I tried out all advice (the easy stuff anyway) so I'm not sure what fixed it. I believe it may have something to do with the sliding pins. The pads are worn more on one end than the other (about 2mm difference end to end), and probably too thin. The pins are now nicely lubed and I moved the caliper back and forth a few times to try to free it up a little. It seemed to move okay. The piston moved back in okay too, but I couldn't do it by hand (I had to use a G-clamp). I think I'll have to whip the piston out at some time - once I find a source for the new seals. On a miata.net page I found reference to "sqealer" springs at the bottom of the inside pad. I checked these and they may have been rubbing, but are unmarked. Are these the "pad wear indicators"? I thought that was a slot cut into the pad itself? Next stop: new pads. (6/01)
It was probably the slider pins, especially as you say the pads were worn unevenly. (Have you checked the rear ones too - even more liable to need lubing!) It's normal to have to use a G clamp to retract the piston (fronts only - allen screw for rear). You can get a seal kit from MX5 parts or from a Mazda dealer, but I don't think it's necessary now - leave well alone. The spring thingies on the inner pad are the wear indicators - they get polished along a narrow edge if they've been touching the disc. They break off if left too long. (6/01)
What's the best thing to lube the slider pins with ? Is it just a case of slathering copper grease all over the calipers, or should you use different things on different bits ? (6/01)
As I've said here before, I do not regard Copper Assembly Compound as a lubricant ( I know some brands call it grease - most don't). OK it /is/ technically a lubricant, but it's designed to stop parts seizing together, not to lubricate sliding components. It is the right stuff to stop pad squeal, and should be smeared /lightly/ on the back of the pads/shims. But for the slider pins I use synthetic grease - Finish Line bicycle lubricant in a black tube from Halfords cycle section. White, waterproof, synthetic, contains PTFE and good temperature resistance. And regrease every 6 months or so. BTW - I've come across an alternative to Copper... for the back of pads. Loctite Brake Disc Quiet. RS list it - you spray it on the back of the pads and leave to set. Not tried it yet, but it might be a good alternative to shims, especially if, like mine, your original shims have fallen apart and you don't get new ones with aftermarket pads. (6/01)
Copper grease is better than nothing, but I prefer heat resistent silicone paste, as the slider pins have to slide withinn plastic fittings. http://www.mobil-tech.de/produkte/si01.htm
Could the pad be rubbing along the circumferal (made up word!!) edge, and not on the disc face? (6/01)