Can I simply top up my brake fluid? so many opinions online but trust you guys

W

wideiris

Well-known member
I have a cbr 125 and my fluid is low. Can i just unscrew the cap and add more? also, are all dot 4 brake fluids the same? (ie - ones for cars are the same as for bikes?)

thanks
 
Yes, and Yes. But, is it low from a leak, or just pads being worn? The reason for it being low matters.
 
Why not just do a full brake fluid change? You will probably have to do it soon anyways if you're running low.

All you need is a tube, a bucket, and a screwdriver. 30 min job if you have no idea what you're doing.
 
You can top it up and all DOT 4 brake fluid is compatible, BUT ... The brake fluid will naturally drop somewhat as the brake pads wear, as someone else has suggested. If you put in too much brake fluid, then when it comes time to change the brake pads, you won't be able to push the caliper pistons back because there will be too much in the reservoir.

As long as it is above the "low" mark or as long as there is at least some fluid visible in the sight-glass, it's OK. If it is actually low, go ahead and top it up, but only to just above the "low" mark or until there is some visible in the sight-glass ... unless you install new brake pads. If you have new brake pads installed, go ahead and fill the reservoir to the top mark.
 
this seems reasonable. thanks. i'll look into how to check the brake pads to see if they're worn. thank you to everyone for responding.
 
Be sure to clean around the cap before removing, don't want dirt getting in there.
 
Brake system is a closed system and unless you have a leak in it, there is no reason to ever need to top it up. The reservoir capacity is designed to be full with new pads and low with pads that need to be replaced.

DOT 3,4 & 5.1 are compatible, DOT 5 is not.
 
^ We have to repeat this for the benefit of those who don't know: DOT 5 is absolutely incompatible with DOT 3, DOT 4, and (confusingly) DOT 5.1, whereas the latter bunch are all compatible with each other but have different performance/temperature ratings.

If you mix a DOT 5 brake fluid with anything else, it will gel up and do a lot of damage! If you want to switch a DOT 3/4/5.1 based brake system to DOT 5, you have to completely disassemble the system and clean it thoroughly with alcohol and dry it out - and then you can't switch back. If the vehicle has ABS, it will generally be impossible to completely bleed the DOT 3/4/5.1 out of the system.

The major difference is that DOT 3/4/5.1 are designed to be hygroscopic - they absorb water - and they turn brownish in the process, giving a visual indication of their condition. Water in a brake system is bad news - it promotes corrosion, and if it gets into a brake caliper, it can boil and reduce brake effectiveness at the worst possible time - when the brakes are being used hard. The bad thing about DOT 3/4/5.1 is that if they leak, they eat paint.

DOT 5 is silicone based. It does not damage paint and it is not hygroscopic. But it is more compressible than the DOT 3/4/5.1 family.

I believe Harley-Davidson uses DOT 5 brake fluid. I do not know if they do that on all models. Practically all other vehicle manufacturers use DOT 3 or DOT 4. I've never seen DOT 5.1 in real life.
 
this may seem like a stupid question but just making sure are you checking it while the bike is straight or angled on the kickstand?
 
Top that baby up, for sure.

But make sure the fluid reservoir is level with the ground, not the handle bars. It will usually mean that you will need for the handle bars to be rotated to the left a bit.
 
PLau said:
Why not just do a full brake fluid change? You will probably have to do it soon anyways if you're running low.

All you need is a tube, a bucket, and a screwdriver. 30 min job if you have no idea what you're doing.
Click to expand...

What's the screwdriver for?
 
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