Disc brakes grabbing / slight shudder

"Mark Shroyer" wrote in message news: snipped-for-privacy@sed.homestarmy.net...

Mark, don't throw $ toward anything BUT rotors and/or pads. I've replaced rotors and many times had to turn (re-surface) them to eliminate the pulsating (the word many of us use--along with some of those "not-so-proud-of words" you mentioned!). ALSO, since you have rear rotors, don't overlook them. If you can consistently narrow down the one culprit, as you felt it to be the right front, then you don't have to work any more--just be around to ride with mechanics/drivers and point out the only one that needs attention to make brakes stop smoothly and truely!:) No flaming intended at all. Just wished to point out it's difficult to even narrow down which "end" has bad, untrue stopping surfaces. So, to check if rears are contributing to pulsating, while driving about 45 on a dry, smooth, uninhabited road, slowly apply the emergency/parking brake. Don't try to bring car to a stop using it, as the rear tires will lose traction so quickly & make you lose control. But, notice while braking w/it only whether you feel the pulsating. If so, they need trueing also. ........didn't think they would, but had to rule on it first. After rear is fixed, test drive and stop normally & see if pulsn. is still present. (If it was ok after emerg. br. test, continue to next step.) Have front (yes, even they are new) rotors trued/turned. Place pads with braking surface down onto a level area of concrete--parking lot, driveway, unpainted shop floor, any place with a surface which will allow you to scrub them so as to rough their braking surface; do this while you let the flatness of the concrete guide the pads during this "truing" process . Continue until the surfaces have turned an even grayish color all over the surface area. Replace and torque wheel lugs to mfg. specs. This torquing is very important. When you now drive the car, avoid quick-stops or riding the brake pedal as you drive. Drive so as to keep the brakes as cool as possible for these formative drives/stops. In OLDER cars, one thing we were taught to do was to "burn in" the new br. linings to mate them to the drum surfaces. This required just the opposite initial driving necessary with disc brakes! All said, yep, I assume your new rotors need trueing. Got a carload (as in "train-car") of drums in last year from China and had to use a drum lathe to true all of them. It was good $ but overly tiring, so the 3 of us took turns (no pun intended) running that process. One of us ultimately dropped out--uh-oh, 'fraid I revealed which one! Don't fault the quality of rotors you got, as I've seen it on both el-cheapos as well as oem's. They're just like tires: I bo't 2 sets of quality Michelins, one set on my dad's Caddy and 2nd set on wife's Caddy. Both rode perfectly at all the speeds we drove BEFORE the new Mich's. After the dealer re-balanced them twice more, I saw some out of round. Quit with him & took both cars to old-timer who still had/used his tire-trueing machine. He trued and then rebalanced-------SEVEN of the eight-------and regained the perfect ride it previously had. Corresponded w/Michelin and was advised the selling dealer did as expected--balance them only; true none, as Michelin made NO untrue tire; and replace none, as all any tire they retailed needed was nothing but balancing. Guess what! Since then, Bridgestone has sold me about 50 sets of mostly-true tires and replaced those untrue ones; Goodyear has sold me around 30-35 sets with almost all perfectly rolling tires; and Western Auto has sold me, who knows, maybe

60-??? sets of unknown named tires with pretty metric treads. These were labeled to run about 30k miles; they actually gave about 55-65k miles. Depending on size, most cost around $35 each--in years 1990-1996. Pardon my diversion. BUT: hth. sdlomi

Thanks for the response. I did try the emergency brake test myself when this started happening (and a few times since then, just to check my sanity), and it's definitely coming from the front. And I should have clarified earlier, it isn't a sinusoidal pulsation that I feel through the brake pedal, like what I vaguely remember from when my last car's rotors became warped: rather, it's the actual slipping, creaking, groaning noise that I feel.

I guess you're right, taking the rotors in to be turned before resorting to new calipers would be a good idea. Still, I'm almost certain there's something more going on here:

1. This problem has persisted in the same form through replacement of both the brake pads and the rotors. And sure, they might be microscopically warped from the factory, but these new rotors are immaculate.
2. Cleaning and relubricating the caliper brackets and pins makes the problem go away entirely for a week or so. The old pins were noticeably worn when I replaced them; and something about even the new pins' action just doesn't feel right, as though there's a gritty, intermittent resistance to it while under lateral force. (Disclaimer: on the other hand, this is the first set of disc brakes I've paid this close attention to, and I really have no idea what it *should* feel like.)

Or am I just making omens from tea leaves? I guess we'll find out after I've had the rotors turned...

Anyway, thanks for the advice! Mark

I agree there's seems to be something more going on here. Your story is not very complete. You imply that you had all the rotors and pads replaced and you did this because the car had a definite and repeatable problem when braking. Yet after the work was done the problem was pretty much the same as before. This sounds a little fishy. Wasn't the mechanic aware of the specific problem that prompted the repair? When the brake job didn't fix the specific problem didn't the mechanic have an opinion on the cause? It seems a little odd that you are asking these questions of strangers rather than someone who did the work and (hopefully) drove the car and witnessed the problem first hand. It's difficult to say what is causing a problem from only a verbal description. You describe it as highly audible. you also mention shuddering that is only felt slightly. So it seems to be mostly a noise. I assume if it was pulling to one side (with or without braking) you would mention that. The problem could be related to a worn or broken suspension component as easily as it could be due to the brakes themselves at least as far as anyone would be able to tell from verbal description. Stuck caliper pistons seems to be the one thing you haven't looked at in the brakes. Also many brake systems have some mechanism to reduce vibration in the pads. It's possible the correct procedure for installing the pads was not followed.

-jim