Why Does My Car Shake When I Brake? Brake Pulsation Explained
“Why does my car shake when I brake?” This is a question that I get almost weekly. In this article we will dive deep into causes of brake pulsation, and how to fix it.
So what is my answer?…. The very, very, short answer?
Your car shakes when you brake due to warping of the brake rotor, deposits on the rotor face, or worn suspension components.
Brake pulsation as it is called can be a really annoying companion when driving. The typical story goes like this ….
“When I am getting off an exit and I hit the brakes the whole car shakes!” What’s the deal? Is it safe?
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In this article let’s cover why you brakes “shake” and even go over things to avoid that can prolong your car’s brakes.
We Will Cover…
Warped Brake Rotors
Easily the most common reason your car shakes when you brake is a warped brake rotor. A warped rotor is no longer straight and true.
Why does this matter?
The brake rotor is what absorbs all of the energy to slow your vehicle down.
The brake pads contact the rotor face under extreme pressure supplied by the brake caliper and brake fluid, this transfers the rolling energy of your vehicle to the rotor.
The end result is heat (the energy needs to be converted to slow you down.)
Here Is a Great Picture of the Brake Caliper, Brake Pads, and Rotor.
The brake pads contact the rotor face using hydraulic pressure, this causes the vehicle to slow down by converting rolling inertia to heat.
The picture above clearly shows the brake pads contacting the rotor face.
As you can imagine, if the brake rotor becomes warped it’s no longer true and straight, applying brake pads at 70 mph is gonna cause some shaking!
As the warped rotor spins it will have high and low spots that the pads will contact.
That in essence is what you are feeling when you car shakes when you brake, the difference in “grab” due to the high and low spots on the rotor.
Brake Pad Deposits
This is not as common as a warped rotor but still causes issues. Brake pads are made of different compounds designed to absorb heat and grip the rotor face.
Typically the softer the brake pad compound the more the brakes “grip” when applied.
This is also the reason many cars (especially european) have a ton of brake dust on the wheels. The pads grip but wear faster.
These soft compounds can build up on the rotor face and cause uneven surface area.
This happens more on vehicles that are driven less and sit for extended periods.
Worn Suspension Components
What about worn parts? If your car shakes when you brake very badly there is a chance a suspension component could be worn.
Control arm bushings are usually the main culprits here. Picture the rotor face being warped and creating a pulsation.
Now picture having a torn control arm busing on top of that, that small pulsation all of a sudden becomes a huge pulsation.
This is simply because that oscillation is not being absorbed as much by the worn component. This in turn amplifies the whole thing ten fold.
If your car is in for service be sure to have the mechanic check the suspension components as well, especially if this is an ongoing issue with your vehicle.
Ways To Prevent “Brake Shake”
Now that we have covered why your car shakes when you brake, let’s go over some ways to prevent this from happening in the first place.
Let’s talk heat!
Too much heat is the enemy when it comes to the brakes on your car.
Avoid “riding the brakes” and sharp hard braking, even having your foot slightly on the brake pedal while driving can significantly decrease the life of your brakes.
Giving yourself time to slowdown before jamming the brakes will also go a long way.
Let’s Talk Service!
If you repair your own vehicle there are a few things to remember when doing your brakes.
Make sure to always clean the hub face where the rotor contacts the hub. If you slap a new rotor on a hub that is corroded and raised up, you will have a pulsation!
Always torque your wheels properly, this is one that many people do not realize.
When you crank down your lug nuts unevenly and over tighten the hell out of them it can create warpage of the rotor face to the hub.
I know it sounds like no big deal but trust me, I have seen it many times.
Always use a torque wrench and tighten the lugs in a star pattern at the proper torque.
How Do You Know If The Pulsation Is From The Front Or Rear?
Determining whether the front, rear, or all four rotors are causing the pulsation is important when you want to fix the brake shake.
The last thing you want to do is guess and spend a bunch of cash on brake components that you very well might not need.
Even if you are bringing the car to the shop, knowing what to tell your mechanic can go a long way. The better you can describe the issue the better your technician can pinpoint and fix the problem.
How To Know If It’s The Front Or Rear Pulsating
Start by safely getting the car up to speed somewhere where you can apply the brakes without getting rear ended.
Next apply the brakes and pay attention to the steering wheel, does it shake back and forth?
The Steering Wheel Will Tell The Story
The steering wheel is only connected to the front end. Under braking with a warped or untrue rotor the steering wheel will shake back and forth quickly. This is due to the front wheels being shaken by the unsmooth braking.
If the answer is yes the front brakes are part of the issue, note I said “Part.” There could still be a pulsation in the rear but when the wheel shakes it’s in the fronts for sure.
How Brake Pulsation Is Fixed
The standard fix for a brake pulsation is to remove the brake rotors and machine them back to a true face.
Keep in mind they need to be measured to make sure there is enough thickness left to allow the rotor to handle heat.
The more standard fix these days is to replace the rotors, prices have come down quite a bit from the old days with rotors.
Both of these options are great. The pads should always be replaced unless they still have plenty of pad material left, at this point you can sand the face slightly to take the glaze off.
Anytime you replace brakes be sure to use quality parts and clean and lubricate all sliding surfaces (never the pad faces or anywhere the pad contacts the rotor.)
When the rotors are installed be sure to clean the hub face to avoid an untrue condition later on.
Wrapping Up
I hope this article gave you some insight to the age old question “Why does my car shake when I brake.”
Now that you know the causes and a little about diagnosing front or rear you can confidently tell your mechanic what you are feeling and where.
If you are a DIY mechanic you can feel more confident ordering your brake parts for this weekend knowing you need em!
Thank you for reading !
