Vehicle application:
- Honda 2003 Element 2.4
Average Reported Mileage:
- 51,000
Customer Concern:
The rear brake calipers are not releasing.
Tools Used:
- Brake pressure gauges.
- Power bleeder (brake system bleeder).
- Scan tool.
- ABS controller and/or electronic parking brake controller (for newer vehicles).
STEPS
Test/Procedures:
- First verify there is no brake pressure to the rear calipers. If there is, loosen the master cylinder and open the lines at the master cylinder.
- If there is no pressure holding pressure to the rear calipers, then verify the park brake is not dragging.
- If there is no pressure in the brake system and the park brake is not holding, then check the caliper slides, and rotor and the pads.
A 2003 Honda Element 2.4L rolls in because the customers complain of a "burning smell" coming from the back and a brake pulsation. When you get the car, the brakes work fine, but you feel a pulsation in the seat when you apply the brakes at over 40 MPH. You do a visual inspection and you see hot spots on the rear rotors, particularly on the rear left one, much worse than that of a typical Honda.
Your diagnosis? Something is making the brakes lock up.
Possible causes? A failing master cylinder, the slides are hanging up, the parking brake is too tight, or the caliper piston is failing to return.
The latter, the caliper piston that fails to return is the most obvious cause. This can be checked easily by removing the caliper from the vehicle and trying to push in the piston.
Let's assume the piston pushes in fine and the slides themselves are lubricated and not rusty (the obvious stuff). Then there are only three possible causes: a problem with the master cylinder, a hanging up parking brake and a brake caliper equalization issue. Cracking open a line at the master cylinder and testing the parking brake for proper operation is simple enough.
You find nothing, so just change the rear calipers, right? You may be right, but you won't be sure. So, let's focus on what to do when we have a hard-to-spot intermittent brake caliper problem that we want to diagnose the right way.
Step 1: Test for caliper equalization
The first step is to test the brake calipers and the hose using a brake pressure gauge. The gauge will indicate how much pressure is on the caliper. When no pressure is applied to the pedal, the gauge indicates zero. As pressure is applied, the needles on the gauge indicate the pressure in psi.
Hickok/Waekon's pressure gauge has a red needle and a black needle that together indicate the amount of residual pressure in the brake lines. The red needle indicates when maximum pressure has been applied to the pedal; the black needle indicates the pressure when the pedal is released. This way, the tech can tell if there is residual pressure in the lines and compare more data sets than a traditional tester.
Other testers simply fit where the brake pads go, making testing as time-consuming as doing a brake job. The Hickok/Waekon kit has a bleeder screw adapter that the gauge connects to, allowing the tech to read the hydraulic pressures without taking everything apart. However, if the bleeder screw is seized, a traditional tester (such as IPA's Disc Brake Analyzer System, No. 7884) is the only type that will work.
Using any brake pressure gauge, simply check the pressure for each caliper and compare opposite sides. If there is uneven brake pressure, this confirms that a brake equalization issue is being caused by a faulty caliper and/or brake hose. At this point, it's fair to start replacing calipers.
After replacing the calipers, bleed the vehicle and do the test again just to verify that it was just a caliper. If you still show equalization issues, then the brake hose on the suspect side needs to be replaced. There is nothing else that can be causing this problem. A bad brake hose often compromises the caliper, so don't feel bad if you changed them.
Step 2: Properly bleed the brake system
Now that you have "condemned" the brake calipers or maybe the brake hoses too, it's time to bleed the vehicle. The old school "pumping the brakes" method of bleeding vehicles is good after a pad slap, but often does not get all the air out when changing vital brake components that introduce air in the system (i.e. brake calipers or brake hoses.)
When changing these parts, in order to avoid a spongy pedal, it is preferable to use a tool that assists in bleeding the brakes. There are a few different types out there that use different methods of bleeding.
Reverse bleeding is injecting fluid at the caliper to force all air up the brake lines and out through the master cylinder. This allows air not to be injected accidentally into the caliper. The level of fluid in the master cylinder must be monitored so it doesn't overflow.
Vacuum bleeding involves pulling air bubbles through the system and out the calipers. We do this by stepping on and off the brakes or by using a machine that applies pressure and fluid via an adapter at the master cylinder.
Finally, there is bench bleeding, which involves a bleeding component not installed on the car, like a new master cylinder. Different tools can bleed vehicles in different ways.
You can do any of these with a vacuum/pressure pump (such as a Matco Tools No. MVP 5000) as long as you have the right adapters. However, some companies make more specialized tools for this task.
Some tools "reverse bleed" the vehicle. One such example of this is Phoenix Systems' MaxPro Brake Bleeder. Instead of pumping the air out through the lines out of the brake bleeder, this tool pushes the air up and out the master cylinder.
The tool is a pump that directly handles the brake fluid, not a vacuum pump that forces the air out the top of the master cylinder reservoir. In just a few minutes, the pedal is firm. This will work on any hydraulic system. It allows pressure, vacuum and reverse bleeding.
With the MaxPro, in order to bleed a master cylinder, a universal port adapter screws onto the front of the bleeder in place of the outlet hose. Push the port adapter into the ports of the master cylinder inlet, and squeeze the handle to bleed air bubbles out.
You can reverse bleed the piece by going in the master cylinder outlets. Pressure bleeding is similar but done on the vehicle. It forces fluid in at the master cylinder and out through the caliper bleed screws.
When the pedal refuses to lose its sponginess, the best technique is to using a combination of bleeding techniques, such as pressure and reverse bleeding or reverse and vacuum bleeding.
An example of a brake fluid exchange tool that vacuum bleeds is RTI's BFX-2 Brake Fluid Exchange System. This tool works by pushing fluid through the master cylinder, while simultaneously applying vacuum to the appropriate brake bleed screw. Fluid is moved from the master cylinder through the lines and out of the calipers, taking any air out with it. In order to pressurize fluid through the master cylinder without creating a mess, the tool comes with a variety of adapters designed to fit the master cylinders of many makes and models.
Other pressure bleeding tools such as the BrakeMate Brake Flush Machine from Flo-Dynamics address the issue of bleeding sequence. The BrakeMate has a "select sequence" feature that allows the tech to select the desired sequence for flushing as specified by the manufacturer.
The BrakeMate Jr. eliminates suction lines and includes a catch bottle giving the tech the freedom to follow the bleeding sequence. It also has an adjustable regulator to increase supply pressure which is required to bleed hybrids and some high end sport cars.
Brakes may be a profitable part of this business and not too difficult to diagnose. However, intermittent problems and spongy pedals can turn customers off, as brakes are one of the most important items on a vehicle. To maintain a good reputation and have no comebacks, the right tools are necessary.
