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Car starts shaking some when braking?

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Old 08-11-17, 11:47 AM
  #16  
leoferus
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There's a lot of information out there about brakes. Here's what matters to us from Toyota/Lexus:

If the runout exceeds the maximum value, change the installation positions of the disc and axle so that the runout will become minimal. If the runout exceeds the maximum even when the installation positions are changed, check the bearing play in the axial direction and the axle hub runout . If they are normal, and if the disc thickness is not within the specified range, grind the disc. If the disc thickness is less than the minimum, replace the disc.
That's step 4C of the front brake inspection procedure. So, let's forget the word warp. Let's call it runout. That's what Toyota calls it. Their engineers have been doing this for a while. I'm sure if they think it's real... it's real. But I am more likely to believe that composite rotors do not develop runout... They just get traded in because most people can't afford to replace them ;-)

In truth, nobody can diagnose your car via the forums. A brake pulsation is a symptom of a condition. You'll need to perform a thorough inspection in order to determine how and why this symptom presented itself. If I were your mechanic I would not start doing anything to your car until I can explain why you are experiencing the condition you're concerned with.

If your brake pulsation manifests itself in a vibration of the steering wheel at moderate speeds, I'd focus on the front brakes. If the vibration is felt more in the seat of the pants, I'd focus on the rear brakes. If the brake pedal seems to be slightly spongy, I'd scrutinize the calipers and hardware... etc, etc, etc.

P.S. I've had more success eliminating runout using an on-car lathe rather than a bench lathe. Toyota recommends the use of an on-car lathe for their products as these machines calibrate to the vehicle and reduce runout accordingly, well, ProCut does.

And not all technicians are the same. Some are much better than others at resurfacing brakes.

Last edited by leoferus; 08-11-17 at 11:52 AM. Reason: Forgot to add something.
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Old 08-11-17, 10:12 PM
  #17  
andper10
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Originally Posted by flowrider View Post
Rotors don't warp. They will sometimes get an even surface from deposits from the pad, but they do not warp. Resurfacing only takes material off the rotor, it's an unnecessary process. Measure the thickness of the rotor to see if replacement is necessary, If it is not. Perform a bedding in process to remove the deposits and transfer pad material to the rotor. Measure the pad thickness also to see if replacement is necessary.

http://www.stoptech.com/technical-su...nd-other-myths
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Good point, technically rather than saying my rear rotor was warped, I should have said that it developed uneven brake pad transfer caused by the stuck caliper slide pin which caused cementite to develop on the rotor surface which caused excessive lateral runout as measured on the rotor and resulted in the rear end shaking under heavy braking. The end result was the same though, it required replacement of the rear rotor, pads, and caliper. I replaced them in pairs since the slide pin on the other side was starting to stick also.

Originally Posted by 2013FSport View Post
Unless you go with synthetic DOT4, the conventional DOT4 is more hygroscopic and absorbs moisture nearly twice as fast as DOT3. Yes, it has a higher boiling point but it comes at the cost of replacement every two years. If your climate has agressive swings from winter to summer it should be done annually.
Thanks for informing me; I have revised my post. I also discovered there are inexpensive
brake fluid moisture content checkers brake fluid moisture content checkers
available.
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Old 08-13-17, 01:52 AM
  #18  
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So its all in a word run out or warped, if you have ever watched brake drums or discs being machined you would see a lot of metal coming off the warped - run out area . I have worked on buses trucks and plenty of old and new cars, in this day and age of throw away society sometimes it makes no $ sense to machine a warped, run out disc which is the major cause of brake shudder.
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Old 08-13-17, 07:21 AM
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Originally Posted by isfvss View Post
So its all in a word run out or warped, if you have ever watched brake drums or discs being machined you would see a lot of metal coming off the warped - run out area . I have worked on buses trucks and plenty of old and new cars, in this day and age of throw away society sometimes it makes no $ sense to machine a warped, run out disc which is the major cause of brake shudder.
Toyota engineers call it warpage at school. We're not seeing materials being deposited on the rotors as being the cause of runout. We're seeing that the rotor surface is undulating. When I resurface rotors with runout I'm seeing a ferrous material coming off the rotor. This might not apply to all manufacturers but Toyota brakes are designed so that the pad deforms rather than the rotor. When the rotor deforms it's due to a number of reasons. In my 10 years with Toyota they have been: 1) Aftermarket pads. The materials used in cheap aftermarket pads cause overheating that can be seen as hot spots on the rotor. Akebono is one of the few aftermarket pads I've seen work well on Toyotas visiting the dealership. 2) Stuck pins. 3) Seized caliper 4) Overheating. Technically, all of the above are the result of various forms of overheating. This one is particular to places that use salt in the winter to combat snow and ice. The vents develop significant rust and this prevents the rotors from being able to shed heat fast enough.... somehow this results in material deposits that result in an uneven rotor surface... or, maybe, they result in warpage... you know, the metallurgical term for a metal that deforms due to extreme temperature change, etc. Anyways, the above not a definitive list. Oh, a major one is that the rotors are close to or below minimum spec. The available amount of material isn't enough to dissipate heat fast enough, therefore, warpage.
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