When applying brakes the brake pedal throbs and steering wheel shakes

Tiny
REED A. BERREAU
  • MEMBER
  • 2011 CADILLAC CTS
  • 3.6L
  • 77,000 MILES
Brake pedal throbs and steering wheel shakes at highway speed when applying brake.
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Monday, February 25th, 2019 AT 5:01 PM

2 Replies

Tiny
CARADIODOC
  • EXPERT
That's an extremely common problem on any brand of vehicle. It is caused by warped brake rotors, almost always on the front. Based on the mileage you listed, it could be time anyway for a normal brake job. Your mechanic will inspect the linings and measure the thickness of the rotors. There is a published legal minimum thickness the rotors can be machined to, then there is another slightly smaller thickness they can be allowed to wear to from normal operation. If the old rotors can be machined and they will end up at least as thick as the minimum specified, they can be reused. If they will end up too thin, they will have to be replaced. If they are machined and reused, that process is what takes care of the pulsing brake pedal.

Due to the high cost of consumables the shop has to pay for to run the brake lathe, the labor time to do that part of the job, and the extremely low cost of replacement rotors today, most mechanics prefer to just replace the rotors as part of a conscientious brake job, and they throw the old ones away. That can end up costing less in the long run.

There is one thing you should be aware of right from the start. A lot of replacement brake rotors come from China, and they develop the same pulsing brake pedal you have now, typically after three months. There is absolutely nothing wrong with the quality of their rotors. The problem stems from what happens after they're cast. When we make parts from cast iron, we set them aside for 90 days to "age" before they get their final machining. The Chinese cast 'em, machine 'em, pack 'em, and ship them right away, then they age after they have been installed on your car. All that is required when the pulsing brake pedal occurs again is for your mechanic to take a light cut on the brake lathe to true them up like they were originally. That rarely needs to be done a second time unless the brakes become overheated.

Every once in a while a hothead demands to have the rotors replaced under warranty. He doesn't understand why the warpage occurred and why it is likely to happen with the second new pair. Just let the mechanic machine them, then they'll last just as long as any other rotors.
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Monday, February 25th, 2019 AT 5:41 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi and thanks for using 2CarPros.

At a minimum, the front brake rotors need replaced. When they warp, your description is the result. I would recommend replacing the brakes and cleaning and lubricating the caliper slides at the same time.

Here is a link that shows in general how it is done:

https://www.2carpros.com/articles/how-to-replace-front-brake-pads-and-rotors-fwd

Here are the directions specific to replacing the rotors on your vehicle. Brake pads replacement is covered in the aforementioned link. All attached pictures correlate with these directions.

_____________________________________________

FRONT BRAKE ROTOR REPLACEMENT (J56)
Front Brake Rotor Replacement (J56)

Special Tools
* J-41013 - Rotor Resurfacing Kit
* J-42450-A - Wheel Hub Resurfacing Kit

Removal Procedure
Warning: Refer to Brake Dust Warning (See: Brakes and Traction Control > Technician Safety Information > Brake Dust Warning).

1. Inspect the fluid level in the brake master cylinder reservoir.
2. If the brake fluid level is midway between the maximum full point and the minimum allowable level, no brake fluid needs to be removed from the reservoir before proceeding.
3. If the brake fluid level is higher than midway between the maximum full point and the minimum allowable level, remove brake fluid to the midway point before proceeding.
4. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle (See: Vehicle Lifting > Procedures > Lifting and Jacking the Vehicle).
5. Remove the tire and wheel assembly. Refer to Tire and Wheel Removal and Installation (See: Wheels and Tires > Removal and Replacement > Tire and Wheel Removal and Installation).
6. If reinstalling the brake rotor, match mark the brake rotor relationship to the wheel hub.

Picture 1

7. Remove the brake caliper bolts (1).

Picture 2

Caution: Support the brake caliper with heavy mechanic wire, or equivalent, whenever it is separated from its mount and the hydraulic flexible brake hose is still connected. Failure to support the caliper in this manner will cause the flexible brake hose to bear the weight of the caliper, which may cause damage to the brake hose and in turn may cause a brake fluid leak.

8. Remove the brake caliper (1) and support with heavy mechanics wire or equivalent.

Picture 3

9. Remove the brake rotor screw (1).

Picture 4

10. Remove the brake rotor (1).

Installation Procedure

Note: Whenever the brake rotor has been separated from the hub/axle flange, any rust or contaminants should be cleaned from the hub/axle flange and the brake rotor mating surfaces. Failure to do this may result in excessive assembled lateral runout (LRO) of the brake rotor, which could lead to brake pulsation.

1. Using the J-42450-A - Wheel Hub Resurfacing Kit , thoroughly clean any rust or corrosion from the mating surface of the hub/axle flange.
2. Using the J-41013 - Rotor Resurfacing Kit , thoroughly clean any rust or corrosion from the mating surface and mounting surface of the brake rotor.

Picture 5

3. Install the brake rotor (1).
Align the match mark made prior to the brake rotor removal, if necessary.

Picture 6

Caution: Refer to Fastener Caution (See: Vehicle > Vehicle Damage Warnings > Fastener Caution).

4. Install the brake rotor screw (1) and tighten to 14 Nm (124 lb in).

Picture 7
5. Install the brake caliper (1).

Note: If reusing the brake caliper to knuckle mounting bolts the threads of the bolts and the threads of the knuckle mounting holes must be free of residue and debris prior to application of threadlocker in order to ensure proper adhesion and fastener retention.

6. Prepare the bolts and the threaded holes for assembly:

* Thoroughly clean the residue from the bolt threads by using denatured alcohol or equivalent and allow to dry.
* Thoroughly clean the residue from the threaded holes by using denatured alcohol or equivalent and allow to dry.

7. Apply threadlocker GM P/N 12345493 (Canadian P/N 10953488), or equivalent to 2/3 of the threaded length of the caliper to knuckle mounting bolts. Ensure that there are no gaps in the threadlocker along the length of the filled area of the bolts.
8. Allow the threadlocker to cure approximately 10 minutes before installation.

Picture 8

9. Install the brake caliper bolts (1) and tighten to 175 Nm (129 lb ft).
10. Install the tire and wheel assembly. Refer to Tire and Wheel Removal and Installation (See: Wheels and Tires > Removal and Replacement > Tire and Wheel Removal and Installation).
11. If the brake rotor was refinished or replaced, or if new brake pads were installed, burnish the brake pads and rotors. Refer to Brake Pad and Rotor Burnishing (See: Brake Pad > Procedures > Brake Pad and Rotor Burnishing).

___________________________________________

Let me know if this helps or if you have other questions.

Take care,
Joe

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Monday, February 25th, 2019 AT 5:42 PM

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