Resources
Frequently Asked Questions
Below are some of the frequently asked questions we hear from technicians on a regular basis. Use them as a resource at your convenience when you are performing a brake job.
Car owners may bring their car into your shop and complain about:
- Intermittent poor stopping performance
- A hard brake pedal
- The brake pedal being hard to depress in panic stops
In these cases, it may feel like the vacuum assist has been lost and the brake pedal is mechanically stopping. You may also hear air escaping from the booster while the brake pedal is depressed.
To troubleshoot this problem, have an assistant start the vehicle and step on the brake pedal several times. While they are doing this, follow the vacuum hose from the brake booster to the intake manifold. The back of the engine compartment between the firewall and intake manifold is typically where the problem occurs.
Feel the vacuum hose. If it is soft or visually collapsing and expanding in response to a change in the vacuum, the hose needs to be replaced.
Master cylinders require bench bleeding before installation. You can do this a few different ways.
Method One (Most Common)
- Mount the master cylinder in a bench vise.
- Connect recirculating tubes into the outlet ports.
- Place the other end of tubes into the reservoir.
- Fill the master cylinder with brake fluid.
- Using an appropriate tool*, stroke the master cylinder pistons using one-and-a-half-inch strokes.
- Repeat this procedure until all air is evacuated.
- Install the master cylinder on the vehicle.
* Make sure the tool isn’t sharp on the end. If you use a sharp-ended tool, you could damage the bore.
Method Two
- Mount the master cylinder in a bench vise.
- Fill the master cylinder with brake fluid.
- Allow the master cylinder to gravity bleed.
- Plug the outlet ports.
- Using an appropriate tool*, stroke the master cylinder pistons using one-and-a-half-inch strokes.
- Once the piston is hard to stroke, the master cylinder is properly bled.
- Install the master cylinder on the vehicle.
* Make sure the tool isn’t sharp on the end. If you use a sharp-ended tool, you could damage the bore.
Brake pedal pulsation can occur anywhere from one to 12,000 miles after a brake service has been performed.
Brake pedal pulsation may be caused by any of the following variables:
- Excessive rotor run-out
- Stacked tolerances
- Hub run-out
- Rust or burr on the hub
- A bent hub
- Improper tightening of lug nuts
- Particles caught between the hub and rotor from an impact gun
- Rear brakes not working properly
Excessive rotor run-out causes the rotor to wobble as it turns. Uneven rotor wear occurs when the brake pad contacts the high side of the rotor. This causes rotor thickness variation, which leads to brake pedal pulsation.
To prevent this from happening, it is important to adhere to the lateral run-out limit. Most vehicles call for .002” runout or less with the rotor installed on the hub. Lateral rotor run-out specifications are referenced in service manuals.
First, it is important to recognize that rotors don’t warp. Instead, they develop thickness variation due to the rotor contacting the pad every revolution.
Checking and correcting rotor lateral runout is vital when installing rotors. Most vehicles call for .002” runout or less with the rotor installed on the hub. Lateral rotor run-out specifications are referenced in service manuals.
If you allow the vehicle to leave your shop with excessive runout, the customer will not immediately notice it because the caliper is sliding freely. The pulsation occurs after the rotor contacts the pad in the same spot over and over, causing a thickness variation. This occurs while driving, not braking. That’s why it usually takes a couple months for pedal pulsation to occur.
By checking and correcting lateral runout, you can save yourself and your clients time and effort down the road.
Use a high temp synthetic lube on all:
- Slides
- Contact points
- Hardware
- Retaining clips
- Metal-to-metal contact areas
Be sure to lube the pad backing plate wherever it touches the caliper housing, including the piston.
The better synthetic lubes have a melting point of three thousand degrees. This causes them to stay in place. Do not use petroleum-based grease as it damages the rubber parts.
The lube allows the parts to slide freely and reduces vibration, which is the cause of noise when the brake pedal is applied.