Pulsating Brakes And An Odd Noise

[ec437]

I've noticed it at lower speeds too (below 50 or 60 mph); it seems that when I brake at least marginally hard the entire car seems to pulsate a little, the speed of the pulsation is in relation to the speed of the car. I got the car up to about 100 or 110 mph today, and when I braked down to about 40 (not ABS panic braking, mind you, but harder than most braking) it was accompanied by a LOUD noise that went along with the pulsation, and the pulsation was very strong. The noise sounded like a low, but loud, hum that would phase out and in very quickly as the pulses occured. Again, the speed of the pulsation/noise was in direct relation to the speed of the car, but the noise didn't decrease any in pitch as I slowed. The noise happened once more when I sped up to 90 mph and braked again. It seems odd because the noise didn't (but the pulsation did, though not as strongly) happen when braking from, say, 70 mph, only about 85+. When braking from 85+ the noise wouldn't go away for as long as I stayed on the brakes (even down past 40 mph), but wouldn't happen if braking from less than 80 or 85. What could it be? ;) Let me know if you need clarification.

[jzz30]

assuming that your rotors arent warped you should check your trailing arms up front and rear. most likely the rear is gone. i did a trailing arm bushing replacement tutorial in the tutorial section, some of your questions may be answered there.

[ec437]

assuming that your rotors arent warped you should check your trailing arms up front and rear. most likely the rear is gone. i did a trailing arm bushing replacement tutorial in the tutorial section, some of your questions may be answered there.

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alright, but rotors don't warp. I'll get my BMW friends to explain it again :P

[92Lex]

assuming that your rotors arent warped you should check your trailing arms up front and rear. most likely the rear is gone. i did a trailing arm bushing replacement tutorial in the tutorial section, some of your questions may be answered there.

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alright, but rotors don't warp. I'll get my BMW friends to explain it again :P

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Rotors don't warp? Is there another name for it or something? Please explain.

[ec437]

assuming that your rotors arent warped you should check your trailing arms up front and rear. most likely the rear is gone. i did a trailing arm bushing replacement tutorial in the tutorial section, some of your questions may be answered there.

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alright, but rotors don't warp. I'll get my BMW friends to explain it again :P

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Rotors don't warp? Is there another name for it or something? Please explain.

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Nope, no other name for it; "warped rotors" is nothing but a myth. Rotors just don't warp.

This page explains it better than I could:

http://www.stoptech.com/whitepapers/warped_rotors_myth.htm

[1990LS400]

Whatever you want to call it - warping, etc. - the undersized front rotors on the 90 - 92 LS400's were unusually prone to damage caused by unevenly and/or over tightening the lug nuts. This was documented in several car magazines in the early 90's.

One more thing. I closely monitored the stopping distances of cars in Road & Track magazine's "Road Test Summary" for several years after I bought an LS in early 1990.

The 90-92 LS400's had just about the longest stopping distance of any cars from both 60 and 80 mph. Very scary for a fast car.

Based on my experimenting with tire sizes, one the main culprits seemed to be the small 205/65-15 tires and this problem was amplified by the poor Eagle GA's that originally came on the car. These tires were so bad that owners brought a class action law suit and I got a check from Lexus in an amount sufficient to by a new set of tires.

If you want far, far better braking switch to 225/60-15 tires and keep them towards the bottom of the inflation range to keep down the harshness - they fit just fine on the OEM 6.5 inch wheels and do not effect speedometer accuracy.

[92Lex]

I guess....uneven wear then.

[Lexus(2)]

assuming that your rotors arent warped you should check your trailing arms up front and rear. most likely the rear is gone. i did a trailing arm bushing replacement tutorial in the tutorial section, some of your questions may be answered there.

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My brakes are pulsating quite heavily from 30 - 70 mph. Assuming it is a trailing arm bushing, how does one tell which one? I cannot discern which wheel is pulsating on my 99 LS400?

Thank-you for your insight.