Problem is on long downhill grades; as I use the brakes more, I get a more pronounced vibration/wobble in the front end (very unnerving on a wet road). Took it in and still had 90+ % on both front and back brakes. Service Tech said it's a known issue...something to do with brakes that aren't heavy-duty enough for the vehicle. Also heard something about 'brake bias' from another mechanic. Considering upgrading to slotted rotors and heavy-duty pads, but don't want to throw away the money if that isn't the problem. Looking for any suggestions that cured same/similar problem.
First thing to check in brake vibration, IMO, is always warped, worn or scored rotors. (Well, pads is first, but that's a visual inspection, no-brainer.) Pop 'em off and check them with a gauge, if you can. If they're really bad, you can just set them on a flat plumb surface and you'll be able to see the problem.
Don't know how long "long" downhill grades are, but if you're heating up the brakes significantly, it might make a rotor problem worse by expanding the rotors unevenly. It'll also make the brakes stickier, which is usually a good thing, but if you've got bad rotors it will also make the problem worse. If you're REALLY heating them up, possibly you just need higher-grade brake pads.
If it's the rotors, you can probably buy OEM-grade rotors for $30 to $40 apiece if you shop around. (You can get them turned, but that's so expensive nowadays that it's just about cheaper to buy new rotors.) Slotted rotors will cost twice that or more. If'n it were my truck, after I checked to make sure everything was tight, tires were properly inflated and in good condition, wheels were balanced, suspension in good working order (the old bouncy-bouncy test, check bushings for play) and so forth, I'd put new OEM-grade rotors on it. If that fixed the problem, swell. If it came back after a short time (short time being less than two years) I'd figure I needed a rotor upgrade and go with something higher-tech. If it didn't, then I'd go with the full rotor/pad upgrade. Sure, I'd be out the seventy bucks, but sometimes you have to gamble.
Mine's a manual tranny, not a 4x4 and no overdrive though. I've driven on some long (more than a mile) downhill grades at highway speeds, like on I-5 down around LA area or coming over the Tehachapi pass in CA, and gearing down was quite adequate for speed control. I also un-learned my bad habit of using the clutch to coast down hills (I coast on off-ramps to decelerate, it seemed logical (back when I started driving) to do the same for hills, boy was I wrong!) Now I'll brake without pushing in the clutch and use the engine for a majority of the braking power on hills. What degree of incline are you talking about? 5% grade, 7%, or worse? Engine whine might be disconcerting but you get used to it.
Had a severe brain cramp (long day) ...it's an automatic trans. Since it sounds like you're familiar with the LA area, I notice it slightly on the downhill in Sepulveda Pass (turning off the O/D here really seems to help) and it's very bad on the grade on the 101 from Thousand Oaks to Camarillo.
It's cool, I knew what you meant. This is a strange one. Heaven knows I'm no expert, but I have to agree with the idea that the rotors are to blame in some way...
1-25-04 No adjustment to wheel bearings on a 98. Are you using your parking brake periodically to adjust the rears so they help with braking? Have you checked the lug nut torque to be sure they are not causing some warpage? Keep us posted. Ed
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