Some pads (particularly some so-called ceramics) can unevenly film the rotors with gummy fillers when they get hot - for example, they get hot on a moderate to heavy usage, then you stop with the brakes held on, and a nice footprint of the pad melts in place. After that, they mimick warped rotors, but the rotors aren’t warped at all - as I said, the problem would then be uneven filming. Sometimes the harsh “bedding in” process is the culprit and creates this problem.
If you have ceramic pads, I’d bet that (uneven filming) is the problem.
The fix can sometimes be to replace the ceramic pads with semi-metallics and use them aggressively for a few days to wear the gummy ceramic filming off the rotors. But if that doesn’t do it, get new rotors and semi-metallics, and the problem will be instantly gone, never to return.
Not all ceramics are bad. It’s just that the term “ceramic” is meaningless when it comes to brake pads (no industry standard for type of ceramic material or minimum requirement for how much actual ceramic material needs to be in the mix), and some of them really are junk, with what I call “gummy” fillers.
Also - make sure there’s no scale rust between rotors and hubs causing a tilt, which will also mimics warped rotors.
My experience has been that so-called “warped rotors” is very seldom actually warped rotors, and is almost always due to uneven filming from gummy ceramic pads (exacerbated by their getting hot, possibly from abusive bedding-in and footprinting when hot), or tilted rotors from rust between rotor and hub.
Solution: Wire brush heavy rust on hubs and rotors and new semi-metallic pads, or if that doesn’t work, the same, *plus* new rotors.
Almost all rotors are made in China these days, but I think China has fixed the problems it used to have of making warped rotors. Very few actual warped rotors out there these days.
I used to have lots of brake vibration problems, but when I finally realized all of the above and started using semi-metallic pads, those problems totally went away.
OH - one more thing - check your inner tie rod bushings for wear. They do wear out periodically on our cars, and when they do, the play in those bushings allows the front wheels to oscillate back and forth when braking at certain speeds. That could also definitely be your problem. (There are some forces on the front wheels pushing forward - due to the combination of the caster angle and the weight of the car on the front suspension, and there are some forces on the front wheels pushing rearwards - such as tire and bearing friction *plus* braking force. When the forward and rearward forces on the front wheels exactly balance - like at certain combinations of speed and application of the brakes, if the inner tie rod bushings have a lot of slop - you definitely will get vibration from the front wheels going into oscillation.)
'98 LXi - Later Concorde gages (black w/ chrome rings)/'99 LX - LHS gages (white) - HIR bulbs
Last edited by peva; 08-15-2018 at 12:26 PM.
Reason: Fix typos