Is it normal for brakes to pulsate

Smith noted that although a brake rotor can warp in many different ways, he never saw a properly assembled rotor warp in a way that causes brake pedal pulsation. He said that, whether on a race car or a street-driven grocery getter, the rotor irregularity that most commonly causes pedal pulsation results from uneven transfer of friction material from the pad to the rotor.

To understand this, we need to understand two basic concepts about brakes. First of all, brakes are designed to work within a specific temperature range and the pad friction material is designed with that range in mind. Secondly, during normal use, friction material abrades from the brake pad and adheres to the rotor, forming an extremely thin layer of friction material on the rotor.

When the pads and rotor are new, the bedding-in process establishes the initial layer. With continued use, the friction material is abraded away from the rotor and replaced with new material from the pad. If the brakes are not properly bedded-in or if the pads are severely overheated at any time, the transfer of friction material from pad to rotor becomes uneven.

Since that layer of material is only microns thick, it can be cut away by a brake lathe. The main reason for replacing or resurfacing otherwise flat rotors is to give the new pads a fresh surface for that thin layer of friction material.

By now the main advantage of on-car brake lathes is well understood: the new friction surface they create is completely parallel to the plane of rotation. This goes a long way towards eliminating comebacks, but with close attention to the details noted earlier, older tools and techniques work just as well.

Before removing the rotor, it should be checked for run-out with a dial indicator. Hubs warp, wheel bearings wear, CV-joints become stiff and cause the stub axle to wobble ever so slightly.

By changing the position of the rotor on the hub, total run-out can be reduced or eliminated. Check it with a dial indicator. Uneven pad wear can show up with a fixed caliper that has a jammed piston on one side. As the brake pads wear, the piston that moves freely will constantly bend the rotor slightly toward the stuck piston. With enough heat cycles, the rotor can actually assume that new shape and the brake pads will wear unevenly. Is pedal pulsation dangerous? But even mild pulsation can influence ABS performance and increase braking distance in a panic stop.

As I accelerate away from the stop my rear brakes pulse or grab making me feel like I have a wheel out of balance if I was going down the road at speed. A few days ago my left front caliper froze up and completely ground the pads down. I replaced the left side caliper, pads and rotor then replaced the right side caliper and pads. Within a few hours the back brakes started locking up. If I was in a parking lot I would just back up and that would get them to release.

But once I stopped for a while they would again lock up or grab. Is this a wheel cylinder issue or a master cylinder issue. Your email address will not be published. Cart My Account Track Order.

All images property of Holbrook Auto Parts. So glad you find the information useful, have a great day! Thank you! Bob Hutchens. Can oil on my brakes make them pulsates while stopping?

Judy matthews. This brings up an important point. The average allowable TIR specification for late-model vehicles is between. This is the maximum allowed! Some manufacturers have specified. Runout will NOT cause pedal pulsation on vehicles with floating or sliding calipers and the caliper housing is free to move and the runout is not excessive.

The caliper housing will move in and out in relation to the runout. This movement will not cause the caliper piston to move. This is a key point to understand. No piston movement results in no fluid movement in the hydraulic system.

So, a key point to understand is runout generally does NOT cause pulsation. Runout causes thickness variation that leads to pulsation problems. Solutions The first solution to solve pulsation problems is to prevent them from happening in the first place. For every brake job, runout and DTV should be measured and documented. This includes pad slaps, machining rotors and installing new rotors. Advertisement Second, pay special attention to the mounting flange. Taking time to clean the mounting flange on the hub can remove corrosion and debris that can cause runout.

Also, pay attention to lug nut torque. Third, take time to service the caliper, slides and hardware. If a caliper cannot float or retract the piston, it can result in increased wear that could lead to DTV and pulsation. New abutment clips are being used on some new vehicles that help to push the pads back from the rotor to reduce drag and allow for less wear on the pads and rotors.

Failing to renew these components as part of a brake job could reduce the life of the brake job and increase comebacks. Advertisement Fourth, using an on-the-car lathe can help to reduce runout. The main advantage of these lathes is that they are able to cut a rotor in its operating plane.

This means that the rotor is machined to match the hub. Fifth, flange runout can be corrected with tapered shims that are available to correct a runout of 0. A runout of more than 0.

The combination of rotor and bearing flange could prevent the rotor from being turned. Checking bearing flange runout should be performed after friction surface runout. Changing the rotor position degrees on the bearing can check flange runout. If the high spot changes degrees, the rotor could be OK or ready to turn after the bearing is shimmed.

Advertisement Components should be marked as you perform an inspection of the assembly. Check the bearing endplay. Mark the relation of the rotor to the bearing flange. Mark the rotor high and low runout spots on the rotor friction surface. The low spot marked as zero and the high spot as 0.

X inches. Mark the high and low runout spots on the bearing flange with the same method and the rotor friction surface. Once you have collected the data, the following comparisons should be made.