Quick question abt break fluid

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DjEyeQ

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I noticed my front reservoir is running very low. Can I just unscrew the lid and top it off? I know theres a proper way to bleed the brakes and fill up, but is just topping up ok as well? The bike is a '03 CBR600RR.

Thanks in advance.
 
I would suggest a full bleed and new DOT 4 fluid.

Educate yourself on YouTube - I did, now I'm a MotoGP "level" mechanic
 
I would check the condition of the brake pads, as the pads wear don t the fluid also goes down in the reservoir.

You may need to replace the pads, if the pads are OK then top up the master cly.
 
In the short if the brakes aren't spongy run you can just top up but I suggest you check for pad wear and full system check. Brake fluid doesn't last forever. If it deteriorates the flush becomes more difficult.

Check you rear brakes as well and the clutch if it's hydraulic. The previous owner of my bike was meticulous in flushing the brakes but forgot the clutch. The fluid looked like gravy.

Brake fluid eats paint and plastic. Use with care.
 
I replaced brake pads in may so theyre pretty new. Im pretty sure the place that did it, didnt do a flush at the time. That little glass piece that shows level is pretty much empty. Brakes seem to work fine but I also want everything to be properly lubricated.
 
Make sure you're checking the fluid level with the bike and the handlebars (clip-ons in your case) in the correct orientation.

As mentioned, brake fluid level drops as pads wear so check the lining thickness. If you add fluid and they need replacing then when you replace them and need to push the pistons back into the calipers you'll need to suck that fluid back out of the reservoir again or it will spill out the top of the reservoir.

If the pad thickness is good and your fluid level is dropping then start looking for leaks, including up at the master cylinder.
 
If your lubricating anything with brake fluid there is definitely something wrong. It's hydraulic fluid, basically it shoves the pistons out to push the pads into the rotors when you pull/push the lever in/down.

I'd flush an fill, then monitor level. You shouldn't be losing any significant amount over a short period of time.
 
DjEyeQ said:
I noticed my front reservoir is running very low. Can I just unscrew the lid and top it off? I know theres a proper way to bleed the brakes and fill up, but is just topping up ok as well? The bike is a '03 CBR600RR.

Thanks in advance.
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Firstly, brake fluid is extremely corrosive and will damage paint and metal components when exposed to water and air. If your fluid is running low then you either need new pads or you have a fluid leak. Check for leaks first. Change the pads second. Brake fluid absorbs water from the air over time and as such manufacturers recommend changing it periodically. Few people actually do this. It has likely been 13 years for your bike so I suggest draining the fluid, refilling it, change the pads and bleed the system. It isn't hard. Be sure to wash the bike thoroughly with soap and water after the brake job or anything the fluid comes in contact with will corrode.
 
thanks for all the help guys. Looks like im gonna do a flush, inspect everything and watch for leaks. Appreciate the help :)
 
Louder said:
I would suggest a full bleed and new DOT 4 fluid.
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what if the bike has DOT 5 in it .. ? ... or then there is the rest of the DOT4 story...

DOT 4 fluids are also glycol ether based, but have a measure of borate esters added for improved properties including increased dry and wet boiling points. A seldom talked about characteristic is that because of this chemistry, the DOT 4 fluid will have a more stable and higher boiling point during the early portion of its life, but ironically once the fluid does actually begin to absorb water its boiling point will typically fall off more rapidly than a typical DOT 3. By FMVSS116 standards, DOT 4 fluids must have a minimum dry boiling point of 446°F and a minimum wet boiling point of 311°F.
DOT 4 is the grade applicable to most race engineered brake fluid in the world today, especially with regard to viscosity limit. Note that although the DOT 4 designation has a minimum dry and wet boiling point, a DOT 4 racing brake fluid may have a dry boiling point over 600F. Its viscosity is challenged, however, to be under the viscosity limit of 1,800 mm2/sec. Some claimed racing brake fluids exceed this important limit. Caution should be exercised if these fluids are used in race cars with ABS systems. This does not mean that DOT 4 fluids are necessarily better than DOT 3 fluids. Remember, the boiling points listed are minimums. There are certain DOT 3 fluids with higher boiling points than some DOT 4 fluids. The real differentiating factor is that DOT 4 fluid should be changed more often than a DOT 3 fluid, because of the effects and rates of water absorption.
 
Also like mentioned, know that the level will drop when you wear out/down your pads. If your pads need to be replaced and you top up now...be VERY careful when you do change pads, as pushing the cylinders back into the caliper will cause the level to rise, and spill down the reservoir.

If you do add now and then do brakes later, I'd recommend using something like a turkey baster to pull out some of the fluid when you are changing pads. Just be careful if you do, that you don't make things so low you suck air into your lines.

Also remember once you break the seal on brake fluid, you need to use it immediately or else it will go bad from air exposure. I forget the timelines, but if a bottle is open more than a week or two you'll likely want a fresh one next time.
 
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If you open a container of brake fluid, top up your bike and cap it back tightly...how is the fluid still in the bottle only good for 90 days? It's the same as in your bike. The reservoir isn't any better sealed than the cap on the bottle.

BF absorbs moisture out of the air, that's what degrades it, not the air.
 
Well because the seal made by the cap to the bottle is not as airtight as what your brake system is, plus depending on how much you use up there is more air content in the partially used up bottle, than what is in your reservoir of your brake system.

your reservoir has a rubber seal, the cap on the bottle does not

by the time I wear out a set of pads, I will replace them, along with a full flush of the lines, so I really never have that much left over, and what is, is used just in case and after that it gets thrown out, next pad change and line flush a new bottle is purchased
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