What can induce brake vibration other than rotors?

My front disk brakes are smooth and vibration free at low pedal pressure and high pedal pressure. But at medium pedal pressure they vibrate. (worse at about 45 mph).

I've had multiple rotors and the last set was premium Raybestos and I even had them trued. It hasn't fixed the problem. I tried changing pads and that hasn't fixed the problem. Caliper pins are lubricated and move freely. All caliper bolts and lugs nuts are torqued correctly. Caliper pistons also seem fine from what I can tell.

What other components can induce a harmonic brake vibration? The wheels are in balance and the hub bearings seem fine.

Can the combination of pad composition, rotor design, wheel and caliper produce a reasonant vibration with no one component being the culprit?

What else can be checked?

Are you ignoring the rear brakes in all this? Don't! Warped rear rotors can cause a vibration too, although it feels a bit different from the
"sawing the steering wheel back-and-forth" feel that warped fronts cause.

How do you know for sure that the hub bearings are fine. I have a 93

Suspension bushings?

"davefr" wrote

Does this happen even right after you have replaced the rotors? Or does it take a few miles or hundreds/thousands of miles to start occuring?

Even torque sticks aren't very accurate. A torque wrench is the most fool proof way to know your tires are torqued properly. I, by no means, don't mean a fool couldn't over torque a lug with a torque wrench. If you don't realize what the click means, you can still over torque the lug)

"davefr"

Doesn't sound like it to me.

Dave, about a month ago I spent too much time talking to a workmate about a vibration in his '98 Bravada. It was about to go out of extended warranty. He had recently had some warranty trans work done (AWD) at the dealer, a bit later a master cylinder and a caliper replaced at an independent shop as part of a brake job, then shortly after that ran over an aluminum ladder on the tollway. A few months later the vibration started happening at 65mph on his way to and from work. Wouldn't happen until after ten minutes or so at that speed.
He bounced from dealer to brake shop to tire store multiple times.
New tires, rims, and brakes rechecked multiple times by the dealer.
Same vibration.
My guess was the driveline - maybe a u-joint or an out of balance/bent shaft. I went for a ride with him at lunch thinking I could at least pin the vibration down to a corner by using my stethoscope. The tollway got jammed before it happened, so we pulled off and came back to work on slower roads. The vibration occurred once, for 4 or 5 seconds at 45mph, but I couldn't get a read on it.
He really likes the Bravada, but was thinking of dumping it because of the vibration and the possibility of uncovered trans work. I told him to keep pushing the dealer, and he did, leaving the car with them for a few days. I figured they would do the driveline work or screw him.
Nope. They replaced the brake booster. Problem solved.
Shows how much I know about modern braking systems, even if I can torque down a caliper bolt.

Not necessarily, no. If you have the original wheel bearings replacing those would be the first suggestion.

It would also help to know whether the vibration begins immediately after pad/rotor replacement or only after some period of wear. If only after wear, it could be as simple as a sticking piston causing hot spots.

If it was my car, I'd trashcan the original calipers and rotors and replace them with good aftermarket ones, and new wheel bearings.

Approximately 8/19/03 09:40, davefr uttered for posterity:

Possible, yes...detectible while driving..maybe not. Do you notice whether the vehicle slightly pulls to one side when you brake?

But if it were any of these components wouldn't they create vibration under non-braking situations??

Thanks for all the suggestions. I can take brand new rotors out of the box and the vibration is there. I even returned the rotors within the warranty period and the replacements exhibit the same characteristic right out of the box. I even had the new replacements machined and the same condition exists.

I guess it could be bearings, tie rod ends, or calipers.

Is there any reliable way to pinpoint the problem to these specific components. Rebuilt calipers after the core refund aren't too expensive but hub assemblies run about $300/pair. Is the "shake the wheel" method effective in detecting a worn hub bearing assembly??

I hate to swap parts without diagnosing the root cause.