Bleeding the Brakes

Bleeding the Brakes

While repacking the wheel bearings, we found a leaking brake caliper. At the same location the brake pads also showed some signs of damage with a portion of the brake pad missing. It’s not clear if that was from something like a rock being kicked up into the area or possibly from the leaking brake fluid getting on the lining.

Although it is usually somewhat easy to replace the brake piston seal and dust seal after honing out the cylinder to remove any places that might be causing the leak we decided to just replace the caliper (Kodiak part number DBC-338-HD-E). Replacing the caliper is much quicker and easier than servicing the original and if you include seals and a set of new brake pads the total cost wasn’t much different since the caliper came with pads.

Replacing the caliper is easy, first you have to remove the wheel, then there are two bolts and two clips that attach the caliper to the bracket. After those are removed the caliper and brake pad assembly can be lifted from the bracket. It may be necessary to use some penetrating oil (I used PB Blaster) on the brake line to caliper fitting to remove the brake line from the old caliper. The caliper can be twisted around as the brake line unscrews to keep the brake line from being kinked.

Once disconnected, hold the end of the brake line up to keep brake fluid from leaking out. Clean the brake line fitting to remove any contaminants that might be introduced into the new caliper then connect the line to the new caliper. As with removal, you can twist the caliper while tightening the brake line fitting to the new caliper to keep the brake hose from kinking up. Do not overtighten the fitting. Reinstall the new caliper on the caliper brackets using the new bolts and clips that came with the caliper. Ensure that the clips are installed properly and that the brake line is not twisted.

I bought a vacuum bleeder kit to bleed the brakes since I wasn’t sure how it would go bleeding trailer brakes and I wanted to be able to do it without another person helping. That didn’t work well. I could get fluid to flow but I could also see air which seemed to be leaking around the bleeder hose at the bleed valve. At that point I went to plan B.

Plan B was to use the breakaway switch to engage the hydraulic pump. Be sure the brake fluid reservoir is full of clean brake fluid of the proper type (ours uses DOT 4) then pull the breakaway cable out to engage the brakes. I bled the caliper I replaced first since I knew it had air in it. When I opened the valve I got a quick flow of fluid ad it was easy to see when the air was removed. Be sure to have a hose attached to the bleeder valve and a container to collect the fluid as it comes out fast. I let about 4 to 6 ounces come out to flush out some of the old fluid then I closed the valve. At this point I reinserted the breakaway cable to let the hydraulic pump rest and cool down.

Now it’s time to bleed the entire system starting at the master cylinder and then moving to the farthest wheel cylinder cylinder away from the master cylinder and working toward the wheel cylinder closest to the master cylinder. During this process I re-bled the cylinder I just replaced just to be sure there was no air left. Before starting each one, make sure the master cylinder is full of fluid – NEVER LET IT RUN DRY! Pull the breakaway switch to engage the brakes and then go bleed the next cylinder using a clear plastic hose and collection container to collect the fluid. Never let out too much fluid without checking the level of fluid in the master cylinder. When done with each cylinder reinsert the breakaway and refill the master cylinder before moving on. When done with all cylinders, top off the master cylinder to the bottom of the filler neck.

Plan C – a better process if two people are available might be to plug the trailer into the truck and have another person press on the brake pedal rather than using the breakaway switch. There should be no need to pump the brakes like you would when working on a car – just press and hold until the person bleeding the cylinder says stop at the end of each cylinder.

Additional information can be found in our post about packing the wheel bearings:

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