Help with RX 300 - Vibration Issues

[Adeyeye]

I Just got a RX 300 and have an issue. in my search for info online i stumbled on this community

 

[Adeyeye]

Can you please help me, my RX300 vibrates the brake pedal when applied at high speed.
the anti skid sensitivity is way too high as it holds me down unnecessarily

 

[Ian Schmidt]

Adeyeye: Assuming the tires aren't excessively worn (which would cause the car to lose traction and the ABS to kick in), that sounds like something a Lexus dealer should be able to fix.

 

[mmcartalk]

Can you please help me, my RX300 vibrates the brake pedal when applied at high speed.
the anti skid sensitivity is way too high as it holds me down unnecessarily

There are several things that can cause a shimmy in the brake pedal, but the usual (and most likely) culprit is what is called "runout" in the brake rotors. That's when the rotors, often due to heat-build up from heavy or repeated use, not enough air-ventilation in their design, or simply poor-quality steel in them, warp into an out-of-round shape and wobble a little as they spin with the wheels. The calipers, of course, which fit over the rotors, also shake and vibrate with them, but you don't usually feel that at lower speeds or until the brake pedal is pressed, which transmits more of the vibrations from the warped rotors through the hydraulic braking system and brake-lines to your foot through the pedal. In typical non-severe cases, you won't feel the vibrations at lower speeds, until about 35 MPH or so, then it will gradually get more pronounced as speed builds. In severe cases, you will feel it at some lower speeds, but with less-frequency because of lower wheel RPMs. In really severe cases, you may even feel it through the steering wheel....but a constant steering wheel shimmy can also be chalked up to other causes within the wheel and tire.

The usual way of dealing with warped rotors is one two things....rotor re-surfacing or rotor replacement. If there is enough metal thickness left on the rotors, and they are not excessively worn (that minimum figure, determined by engineers, is measured with a micrometer, and is available in the vehicle's Service Manual) the Service Technician can take the rotors off the car and place them on a machine, somewhat similar to a metal-lathe, that will shave the uneven metal off the rotors, true them up, and get them to spin smoothly again without runout or vibration. If the rotors are excessively worn beyond that minimum figure, a reputable brake-shop will not put them on the lathe (truing up badly-worn rotors could be risky or even dangerous), and brand-new rotors will have to be used....a somewhat more expensive proposition, especially for an upmarket vehicle like a Lexus) but usually safer in the long run. Often, with new or re-finished rotors, it will make sense to also replace the brake pads, as the pads may also be unevenly worn from the vibration, and it would make little sense to try and match them up with new or re-finished rotors.

So, while your shimmy-problem may or may not be 100% traceable to this specific cause, if it is in fact the rotors, don't be surprised if you end up needing at least a partial, if not a full, brake-job.

As far as the anti-skid feature (ABS) goes, THAT pedal-vibration is due to another cause....one that is usually perfectly normal. As long as the tires still have traction on the road when you press the brake pedal, the brakes will function without the ABS feature....and, if the rotors are true, the pedal will respond smoothly. But, if and when one or more of the tires loses traction on a slick surface (and here's where Ian Schmidt's comment, above, comes in) the ABS computer will sense an impending wheel lock-up, and rapidly pump the brake to that wheel on and off some 100 times a second....far more rapidly than you could manually with your foot.....to keep the offending wheel or wheels from locking up and causing a loss of control and steering. As Ian suggests, the more the tires are worn, the less traction they are likely to have on wet or slick surfaces, and the more likely the ABS function is likely to kick in, especially under heavy pedal-pressure. So, it's (possible) that you may not only need brake work, but new tires as well.

 

[mikeavelli]

Can you please help me, my RX300 vibrates the brake pedal when applied at high speed.
the anti skid sensitivity is way too high as it holds me down unnecessarily

I'm with MMarshall, sounds like a warped brake rotor.

 

[crankshaft]

Re-balance all tires

 

[mmcartalk]

Re-balance all tires

Welcome to Lexus Enthusiast as a new poster.

Sorry to disagree, but tire balance doesn't usually cause a shimmy in the brake pedal. Far more likely are out-of-round brake rotors, caused either by heat-buildup or by uneven deposits on them. Or, if it is the type of vibration the OP mentioned from the ABS, that's caused by the rapid-pulsation of the brake-system some 100 times a second. That's programmed into the ABS computer.