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Squealing is usually fixed by spreading anti-vibration goop on back of pads, together with mfr.'s backing plates of light sheet metal. Saab doesn't recommend turning rotors, and I agree with them. Unless done by a real careful pro they can come back out of round and worse than before, and every time they're turned you lose thickness, life, and stability against warping.
If they're really worn or badly rusted or so out of round that they're making pedal pulse, THEN replace them, and my advice is, with OEM rotors. There can be big differences in longevity to wear, in resistance to rust, and in resistance to warping, and it's worth the extra peace of mind.
Do they really need changing? I've used some really deeply grooved and hellish rough rotors before out of necessity (after pads ran down to iron and caught and galled them) and with new pads on, checking just a day later, surface had smoothed out so much under new pads that I kept running them; couldn't tell any difference in brake feel, no pulsing, and both sides even, no pulling. After all, they go round and round, the grooves on rotor match grooves in pad, and they don't need to be platter-smooth. (It even gives you more braking surface!)
If those were Saab's own rotors, new 5,000 miles ago, and if you're not feeling a pulsing brake pedal, I'd leave them alone.
As to calipers: There is no reason not to simply replace the bad one; don't do both of them.
Calipers can be fixed sometimes: The pistons sometimes cock in their bores, usually when over-extended because someone has turned a rotor to below its minimum thickness and then as pad wears down, piston comes out of its hole too far and cocks sideways and won't slide back. Then it gets worse if it stays there as rust and road dirt build around it and lock it in. But the clever DIYer can sometimes free them back up, by prying (rarely) or by this trick if you have an air compressor: Use a "rat-a-tat," an air chisel, with a round-tipped chisel blank chucked up instead of a chisel, and angle it in and onto the top of the piston and let 'er rip. Maybe use an old pad as intermediate spacer. The vibration will help get it moving back in; once it's pushed back home, without pads in, get someone to just tap pedal to extend it again some (DON'T blow it out of its bore) and then push it home, this time with C-clamp or my favorite tool, a wrecking bar prying between caliper and rotor. Work it back and forth a few times. If it doesn't leak, and you'd see that immediately, it should be fine.
Stuck calipers happens more to rear brakes, in northern rust climates. As they bear so little of the braking load and move so incrementally, for all intents and purposes they're standing still all rust season and get rusted into place. The above fix works on them too because the rust is in the outer part of the bore, well out past the seals, and the pistons are on almost all makes of cars made of stainless steel and not rusted themselves.
But generally, it makes good sense to replace a stuck caliper. You can go either used, rebuilt, or new. Used would be most economical and to my mind there's no qualitative difference, if they look good and not heavily rusted externally.
As to the pads: Certainly, replace them. They're cheap, they're already used to some fraction of their original life, and even if your mechanic is only fixing one stuck caliper, he's having to remove the old ones anyway.
As a DIYer I've re-used pads but only if they've got lots of meat left on them and if my only way to get to an auto parts store to buy new ones is up on jack stands in front of me.
posted by 70.105.226...
, Thu, 13 Jan 2005 11:03:05
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