Replace brake pads on motorcycle open brake fluid lid or not

Question

I have been meaning to replace the breakpads on my Honda XR125L. I've done it before on my VW Jetta.

The thing I'm confused about is whether or not I have to open up the lid of the brake fluid container. I've seen guides online that do, and guides that don't.

The way I see it, if you open up the container for the brake fluid you can more easily push in the piston of the brake clamp? If you don't it will be harder.

On the other hand, I'm not sure if it's a good idea to do so.

And in the end, will I be able to push in the piston by hand? I recall having a really tough time doing it with my car given that I don't have the clamps that do it for you.

Answer 1

If you're just trying to replace the brake pads, then opening the brake fluid reservoir won't make any difference. Regardless, it will take some time for your new brake pads to gain some bite. It's recommended to open the brake fluid reservoir only when you intend to drain the brake fluid and replenish it with new stock, followed by bleeding the braided brake lines/cables.

On the other hand, if the fluid has already reduced beyond the limit/mark on your brake fluid reservoir, then, it should definitely be changed.

Answer 2

You can open the lid but I imagine its located on the handlebars somewhere so you should lock the handlebars to prevent any chance of movement/spillage.

However, I would recommend opening the bleed screw (if it is not corroded), and then compressing the piston. This will push all the old fluid out through there instead of back up the brake lines. This gives you a chance to add some fresh fluid and bleed the brakes, making your brake job more complete. The brake fluid that will come out will be the stuff that stays in the caliper and brake hose so it is the most exposed to heat and moisture. It should be replaced anyway as part of scheduled maintenance so why not do it with the pads?

I would also invest in some clamp to push the piston back in. It helps make sure the piston goes back in straight and its easier. There are special tools for it but I just use a C-clamp and the old pad for cars, not sure if this will be suitable for a bike.

Answer 3

Probably not.

The answer depends on how much friction material there was on the pads and how full the reservoir was filled the last time the fluid was changed. If the pads were 1/2 gone, and the reservoir was filled to the full line, brand new pads will be thicker, and the fluid will have to raise above the full line to accommodate them. Depending on your reservoir, this may be possible, but the reservoir is sealed with a rubber diaphragm under the cap, and at a certain point you're going to run out of room in there.

I would try cleaning the calipers (specifically the pistons) with warm soapy water, then let them dry. Afterward, push them back into the calipers while keeping an eye on the fluid level. You can use the old pads to help give you something to get your hands on. If your pistons and seals are clean and in good condition, you shouldn't have any problems doing this with your bare hands. If the reservoir hits the full line and you still need more room, then you'll have to take some fluid out.

Any time you have to open the cap of the reservoir, or anytime you need to change brake pads, is a good excuse to change the fluid and bleed the system. Brake fluid is a cheap, and it's a relatively easy job.