Help Pls: Steering wheel shaking/vibrating on braking at high speed
Lately my 2007 GX470's steering wheel has a shaking/vibrating problem whenever I apply the brake at speed above 50 mph or so. Without braking or with braking at slower speed, there is no problem at all -- everything is glass smooth.
1. I assume the front brake rotor is warped?
2. Will I need to change the rotor or is there a way to fix the warp (it that's the problem) without changing the rotor?
3. Approximate part & labor cost?
I plan to bring to dealer for a check up but would like to know ahead of time what to expect. Thanks in advance.
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Here's something to try, as long as you think it's safe. The theory behind this is that a lot of rotor "warpage" is actually just uneven deposits, typically caused by the pad fusing to the rotor after a hard stop.
So, what do you want to do? Heat up your rotors good & hot and then let them cool.
Find a deserted road
Accel to 60 or 70mph
Brake hard to a near stop (ideally downhill == more rotor heat)
Repeat step 1 once or twice
Again, you're trying to get your rotors very hot.
Then, drive carefully for 15min or so without sitting stopped w/the brakes "on".
I was developing a bit of a warp on my GX, and recently was able to clear it up with the process noted above.
Intersting you say it's "glass smooth" at low speeds. In my experience with warped rotors there is at least pulsing and even a more pronounced steering wheel shake at slower speed and when coming to a stop. I would suggest having your tires rotated and balanced before spending money on new rotors etc. It's recommended anyway in order to prolong the life of your tires, but it also maybe an underlying cause to your problem. The symptoms of an out of balanced tire can be exasterbated when applying brakes. If you have this done at Lexus ask them to measure the "run-out" of your rotors, which will tell you with certainty if they are warped. The chances are it's the rotors, but the rotation is an inexpensive "potential" fix to try and if anything you extend the life of your tires. Good luck.
Yes theoretically this definitely sounds like a text book brake pulsation. Most of the time a pulsation will be felt at all speeds, but alot of times with "higher end" vehicles, ie, your GX. Rotor warpage sometimes is not felt at lower speeds, due to rotor and pad material.
Your rotors need to be mic'd, or measured, to see what their thickness is. Your vehicle will have a minimum spec under which they will not be able to be turned or machined. Your car is fairly new though, I would guess that the rotors are well above spec, unless there is above average mileage involved.
hope this helps...
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guys, seriously, try the procedure I outlined above -- it's free and might even raise your pulse a few ticks.
I've "warped" my rotors at least 3 times in the 40k miles on my GX, and cured them each time w/the procedure above.
Little known fact is that in the majority of the cases what people perceive as warped rotors are actuallly pad deposits unevenly distributed on the rotor -- typically due to leaving your foot on the brake after a hard/fast stop and "baking" a bit of the pad onto the rotor.
What do you mean by "uneven pad deposition?"
Virtually all modern brake pads are what are referred to as an Adherent type of pad. The pad is designed to transfer a layer of pad material onto the rotor. When a sufficient and EVEN layer of pad material is adhered to the rotor face, the pad material on the rotor, interacting with the similar material on the pad, creates the most efficient friction mechanism. These like materials, breaking against each other on a molecular level are what really stops the car well. To emphasize, there is supposed to be a layer of material pad material on the rotor. The problems occur if the pads are not properly bedded-in (an even layer of pad material on the rotor) and run aggressively, OR if the pads are overheated (street pads on the track like we tell 37 people a week NOT to do). The pad transfer occurs most efficiently at the pads optimal operating temperature. That means a higher temperature pad needs to be hotter to properly transfer material. If you have a high performance pad and never run it hot enough to get a proper layer of material onto the rotor, it will never be properly bedded-in. Thus, even after 1000 miles of "normal" street driving, when you blast your favorite canyon and heat the brakes, you can get uneven deposits on the rotor causing a vibration. The other common scenario is over-heating the pads even if they are properly bedded-in. In this case, the pad material starts to break down and smear onto the rotor face, again causing the UN-EVEN deposits. The other problem that occurs is if the system is really hot and you come to a complete stop and leave your foot on the brake pedal. In this instance, we get what is called "pad imprinting" where a small layer of material breaks off the surface of the pad and literally can be seen as an imprint of the pad on the rotor face. This can occur no matter the state of bed-in. All these scenarios leave very small, uneven layers (we call it TV, Thickness Variation) of material on the rotor. We're talking a few 10/1000's of an inch, like a TV of 0.0003". It starts out almost imperceptibly, but as the pads start to skip over the high spots, more material is deposited on those areas, ever increasing the vibration until it becomes quite noticeable, even days after the event that started it occurred. The best way to avoid these problems is proper bed-in of the system initially, and using the proper pads for your exact driving conditions. If you are planning on swapping pads for a track day, you need to re-bed the system before the event (or dedicate the first track session to bed-in). Remember, you have that layer of street pad material adhered to the rotor face, and if you don't remove and replace it with the track pad material, it is going to degrade from the heat and... yep, cause uneven pad deposits. Same goes when you put the street pads back in, you need to re-bed them for optimal street performance.