Car Pulses While Braking?

[andersen_james]

In case anyone out there is still looking for answers on this ... when there is a shimmy or shake in the steering wheel when braking at higher speeds, it *could* be a warped rotor if the rotor has many thousands of miles on it, but if the rotor is new, the likely cause is improper brake-in of the brake pads and rotor. The break-in procedure ensures that a thin layer of the brake pad friction material is evenly distributed on the rotor. If the material is unevenly distributed, there will be spots where the brake pads grab more, and spots where the brake pads grab less on the rotor, which results in grab-slide-grab-slide-grab-slide which is felt as a strong shake at highway speeds, but less pronounced at city speeds.

Never use old pads with a new rotor, and when installing new pads, always replace the rotor or have it turned, and follow the brake pad manufacturer's brake-in instructions exactly as written. Higher-end ceramic pads like Akebono do not require a break-in procedure, but braking needs to be gentle for the first 300-500 miles to prevent hot spots on the rotor.

It is very rare for a rotor to be warped unless you are a street racer constantly going from 100 to 20 miles per hour and your rotors stay HOT for prolonged periods, but if you were a street racer, you would be using performance rotors that could handle it!

If the vehicle has a shake at highway speeds without the brakes being applied, things to check would be a bent rim (even slightly out-of-round will cause a big problem) or a bad tire. Bad tires are not easy to identify just by looking. The tread may look great and there may be no obvious indicators, but putting it on a dynamic balancer will help reveal the issue. And speaking of dynamic balancer, if you lost a tire weight, that would do it as well (and be the easiest to fix!). A ball-joint with any play can also contribute (or any other loose suspension part), but is usually only a consideration on a high mileage car. Of all the above, the most likely reason for a wobble or shake during high-speed braking is an uneven braking surface on the rotor due to low quality brake pads and/or improper break-in.

If you feel a 'chatter' in your brake pedal only when braking at low speeds (<10 MPH), it may be a bad ABS wheel sensor. If it happens only when turning at low speeds, it is likely one on the front; otherwise, it could be any of them. For Lexus, they are not too difficult to remove, and you can Google operating specs and take them off and test them one at a time. They are held in place by a single 10MM bolt, so if you have an older model car subject to winter road-salt, it could break, so have a drill, tap, and new bolt handy just in case! 

These are just some high points, some of them already mentioned above, that I hope someone finds useful.