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 hoses 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.
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. To be more exact with your diagnosis, consult the chart on page 14.
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.