Phil Krolick – AutomotiveBack to Instructor Webpages
Disc brake calipers may need to be removed in order to replace the brake pads, remove the rotor, or accurately measure rotor thickness and runout.
Often you can remove the caliper without pushing the piston or spreading the brake pads.
When this is the case, you only need to remember this…
.... NEVER ALLOW THE CALIPER TO HANG BY THE BRAKE HOSE.
Flexible brake hoses can be damaged if they are stretched or kinked.
The damage may not be visible from the outside however any internal damage can cause the brakes to pull. This can happen as the brakes are applied, or as they are released. (it depends upon the direction of the flap)
Always use some type of hook to hang the caliper so that the brake hose is not stressed.
Notice the metal wire hangar in the photo above. DO NOT allow the caliper to hang on the brake hose. It may damage the hose and cause braking problems.
Upon occasion you will need to spread the brake pads to allow room for the caliper to come off.
It is important to Gently force the piston back into the caliper housing.
If you do not open the bleeder screw first, old and contaminated brake fluid will be forced backwards or UP towards the Antilock Brake Modulator and Master Cylinder.
Upon occasion this will cause the ABS brakes to malfunction! To avoid this always open the bleeder screw, and use a brake pedal depressor to keep contaminated fluid from being forced back into sensitive valves and antilock brake components.
Using a brake pedal depressor to hold the brakes ON will block any fluid from moving backwards through the hydraulic system. Opening the bleeder screw will relieve the pressure in the brake lines and allow the caliper piston to move out of the way.
Below is a picture of the brake pedal depressor tool. Notice it is next to a brake drum that has been removed as part of a normal brake inspection.
DO NOT PUSH ON THE BRAKE PEDAL IF THE BRAKE DRUMS ARE REMOVED!!
If the brake pedal is pressed while a brake drum is removed it is very easy for the wheel cylinder to over-expand. If the small piston(s) inside the wheel cylinder pop out you will need to replace the cylinder. It is possible to re-assemble the piston and seals into a wheel cylinder however re-using seals often lead to leaking brake fluid. Once brake fluid leaks into a drum brake, the brakes will grab and pull. The only fix for this is to replace the brake shoes and wheel cylinder. DO NOT ATTEMPT to repair a wheel cylinder. You are responsible for the safety of the braking system and the passengers of that vehicle!
By installing a brake pedal depressor you are blocking the vent port in the master cylinder. This will not allow any brake fluid to move backwards through the hydraulic system.
Once the bleeder screw is opened it will relieve any hydraulic brake pressure and allow you to slowly press the piston back into the caliper housing. Brake fluid will get forced out the bleeder so be ready to catch the brake fluid in a container. If any brake fluid spills, be sure to wash it up using plenty of water.
As you can see there are several ways to successfully remove a disc brake caliper without causing any damage to the flexible brake hoses, or forcing contaminated brake fluid back into sensitive ABS valves.
Notice in the picture below, a creative caliper hangar and the brake fluid from the bleeder screw.
It is not unusual to replace disc brake calipers with new or rebuilt units. Often it is most effective to purchase "Loaded" calipers that already have new brake pads, shims and clips installed and properly lubricated.
Many brake hoses use a Banjo Fitting (shown below). If you remove any hydraulic brake line that uses a copper washer, it is important to use new copper washers every time! Re-using the copper washer may cause a small brake fluid leak. Also notice the hollow bolt. Brake fluid travels through this hollowed out bolt. Be sure to use a torque wrench with banjo fittings. The hollow bolt is easy to stretch or break if a toque wrench is not used.
Finally, Remember to always use a brake pedal depressor if any brake line, caliper, or wheel cylinder is being replaced. With the brakes applied, the vent port in the master cylinder is blocked. This will keep the brake fluid that is in the open brake line from running out while the brake line is disconnected. If the brake fluid drips out of the brake line, it is replaced by air. Extra air in the brake lines, and especially in the ABS modulator valves, can be very difficult to remove when bleeding the brakes!
When installing a caliper back onto the vehicle be sure to torque mounting bolts to spec. Some mounting bolts have a very low torque and it may be a good idea to use blue Loctite on those bolts.
Before returning the vehicle to service, step on the brakes several times. This will reset the brake pads to their normal operating position. Before the brake pads are re-set, the pedal will sink to the floor. After one or two pumps, the brake pedal should be firm and have acceptable pedal reserve. After this the pedal should never go lower than normal.
The brake pedal should not go to the floor and have a firm and consisted feel. If the pedal is spongy there may be air in the lines. If the pedal is consistently low check the adjustment of the rear drum brakes. If the pedal slowly sinks to the floor, be sure to very carefully (use a good light) check for any signs of brake fluid leaking at any place you have disconnected a brake line, or opened a bleeder screw.
DO NOT allow the vehicle to be returned to the customer if the brake pedal does not have a normal feel to it with plenty of pedal reserve!
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