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  #1  
Old 01-31-2002, 11:58 PM
cossie
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weird brake sound/sensation

Recently I've noticed this odd sound/feeling when braking. Actually, I'm not even sure if it is a sound; it's more of a sensation that my foot can feel. It comes on intermitently. Here's a brief history:

I had a complete brake job (all pads and rotors) performed about 3 or 4 months ago. There has been no sign of brake problems (e.g., grinding, squealing, rough scratches on rotors, leaks, etc.) since this service was done. My brakes work fine, and the pedal feels firm when I step on it. My concern is this barely noticeable "pulsating" feeling I sense sometimes when I come to a stop. I don't think it's the ABS working because the pulsating is very, very weak--but I can still sense it. I can't really describe the sound (if it is a sound) or feeling. It almost seems like it may be coming from the engine or drive train, as if one of them is "braking" too.

My second guess is that it's a tire problem. My front tires are worn almost treadless on the edges, and I'm not sure if they may cause the weird braking feeling. Perhaps they are trying to grip the road when I brake. However, I don't feel any sliding; my car stops correctly and there is no steering wheel shake.

Should I be concerned about my brakes? I've checked my rotors, and they don't look scratched unevenly. My brake fluid level is fine; however, it has decreased only slightly since my brake service. I'm just concerned about this braking sensation I've noticed recently. I've never noticed it before. What's also worrying is that it is inconsistent; it happens randomly. Any comments is greatly appreciated. I need to rid myself of worries.
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Old 02-01-2002, 01:28 AM
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Join Date: May 1999
Location: Sacramento, CA
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Well, if it's not warped rotors or bad tires, could it be an uneven idle? My car idles unevenly, and sometimes when I'm slowing to a stop I can feel the car surge briefly (and repeatedly), which would give the symptoms you describe.

Just a thought..

-anthony
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Old 02-01-2002, 01:54 AM
cossie
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What are some signs of warped rotors? Hmmm, my two front tires are going bald at the edges, could they be the culprit? And the fact that you mentioned an idle problem...my car idles fine, with no fluctuation. It does, however, idle roughly just briefly upon start up in the cold morning. It idles perfectly otherwise, even when slowing down to a stop. I know my car is due for a tune up, so maybe your idle comment makes sense.
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  #4  
Old 02-01-2002, 02:57 AM
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Join Date: May 1999
Location: Sacramento, CA
Posts: 1,472
Warped rotors will give you a lurching brake effect, as if the brakes grabbed and released rhythmically. (Which, essentially, they're doing as the warped rotor will give varying amounts of contact with the pad as it rotates) I don't know if the tires would really give you a pulsing effect through the pedal, more likely through the steering wheel.

If your idle is fine, then I would doubt it'd be the cause of your braking problems. You'd notice an uneven idle, especially at a stop. (At least, I did...)

anthony
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  #5  
Old 02-01-2002, 03:00 PM
Van Helden
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Are you sure your rims/wheels are properly torqued? If not, this could restrart the process of warping you rotors. Secondly, I'd put on some new tires. Hope this helps!
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  #6  
Old 02-01-2002, 03:18 PM
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Pulsing brake pedal is the classic warped rotor symptom, and the fact that you just had brake work may point to them. Did the shop machine (turn) or replace your rotors? If they machined them, they may be too thin and, hence, prone to warp. Are the lug bolts torqued to specs? Some shops overtighten lugs and uneven lug torques can actually warp the rotors and cause pedal pulsation. I'm not too keen on the lumpy idle theory -- you feel it in the brake and the idle feels smooth at rest, right?
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  #7  
Old 02-01-2002, 08:03 PM
cossie
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what are some visual signs of warped rotors? My rotors look smooth and even. BTW, these are all new rotors.
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  #8  
Old 02-02-2002, 12:05 AM
Van Helden
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Jdoyl is right on I think. Go back and find out what they did at shop or look at your receipt. Either way I would retorque. You won't see if they are warped except to look at the rotor as they are turning them on their lathe. These differences are measured in thousands of an inch inspite of their smoothness.
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  #9  
Old 02-02-2002, 01:09 PM
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Join Date: Dec 2001
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You can detect a warped rotor by measuring the lateral runout using a dial indicator, a micrometer that mounts to a stationary part of the car and detects lateral runout in the rotor as you turn it by hand. You could have defective new rotors, or the rotors could have been improperly installed, over rust or dirt, and not mounting flush and flat. Assuming you don't have access to a dial indicator, you could go back to the shop that did the work and ask them to check in this way. I wouldn't assume that just because the rotors are new they are blameless. Good luck.
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