How to separate stuck together brake pads - Honda CX500
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Someone goofed. Maybe it was you, maybe it was an assistant, but someone pulled on the brake lever when the caliper was off the rotor and now the brake pads are pressed together extremely firmly.
There's no chance of fitting the brake rotor back between these as when you try to push them apart you're trying to compress the fluid in the brake lines far enough to squeeze the rotor back, which isn't going to happen. The above situation is a best-case scenario for this happening - the brake pads were new and the brake piston behind them had not pushed far enough out that it was leaking brake fluid and allowing air to enter the system. If that happens you need to re-bleed the brake lines. In the above situation, though, we can get away without doing that.
Grab a wrench for the caliper bleed valve (8mm is close in metric sizes if you don't have any imperial wrenches), a glass jar, a small amount of brake fluid, a short length of fuel line and a flat chisel or other tool for prying the pads apart with minimal damage. Since we will be playing with brake fluid you will also need at a minimum eye protection - we like gloves as well, as who wants brake fluid on their skin? - and be careful not to get any on paint or anything else valuable! Check that the brake master cylinder reservoir is topped up, as the process of pushing the pads together will have drawn fluid from the reservoir into the lines. Then, choose a bleed valve to attach to. If you only have one front brake caliper there's no choice, but if you have dual discs you can attach it to either. Why? It's a closed hydraulic system, so any force exerted will be equally distributed through the system - meaning that it doesn't matter whether you release the pressure near to or further away from the brake pads. Using the other caliper can be handy if you're a one-man operation as it's already firmly attached to something. Attach the tubing to the top of the bleed valve of your choice:
Pour a couple of centimeters of fresh brake fluid into the clean glass container (jam jars work well) and put the other end of the tube into the fluid. If you're a one-man operation kludge together a way of keeping the line in the fluid:
Close-up you can see the other end sitting in the fluid:
Position your prying implement between the brake pads;
Apply firm pressure, attempting to separate the pads with one hand and at the same time crack the bleed valve open a quarter of a turn with the other hand. Be careful not to butcher the pads too much with a sharp edge in the process. The flatter and broader the implement, the better. The pressure created by pushing back against the brake pads will be released through the bleed valve, causing some brake fluid to flow into your tube:
Without much effort you should see the pads separate:
This is how much fluid was lost in the process:
Once the pads are far enough apart to get the rotor back on...
...close the bleed valve:
...then remove the tube, put the caliper back on, check and double check all of your bolts and bleed valves, check the fluid level in the master cylinder reservoir and check that the brake system is functioning properly.
All done!
