Topping off Brake Fluid....

[Jadien]

Ok, I've been looking up topping off my brake fluid (I'll change it in January when my loans come in). But, I haven't found anything talking about just adding fluid. I even looked at my bikes service manual, and all it talks about is changing it out.

So.......:

1. Do I just open up the resvoir and pour it in?
2. Do I have to bleed the system?
3. Anythings else of importance I should know about?

Thanks,
Dave

[Sev]

If the level is low just pour some new stuff in the top. If you're trying to change out the old stuff then you need to bleed the lines.

Make sure that you put the right kind of brake fluid in there:

DOT3, DOT4 and DOT5.1 are compatible, but they all have different boiling temperatures.

DOT3 boils the lowest, DOT4 is good to a greater temperature. I am unsure of DOT5.1. It is generally preferable to run DOT4. Do not run DOT3 in a DOT4 system.

DOT5 is not compatible with any of the other fluids, it is "race fluid" and if you mix it with any of the other fluids you can run into several problems including clotting, contamination, or even have it start to eat into seals and lines. DOT5 is also NOT hygroscopic, which means it does not absorb water. This seems like it would be a good thing, but it's actually bad. This means that water will actually pool in the calipers where it can boil off under heavy braking - causing air bubbles that affect brake performance. It can also contribute to rust inside the calipers.

If you need directions for bleeding the lines lemme know and I can dig up the bloggy post on it

[slimcolo]

Sev your description of brake fluid is correct except calling dot5.0 race fluid. If it's race fluid how come the motor company has used it since the 50s on all juice brakes ? (drum and disc) Other manufacturers also use dot 5.0 (Panzer, Castle,CMC.........etc) as a general rule japanese bikes (my last one w/juice was a 76) used dot 3.0, European (bikes and VW) use dot 4.0 and America 5.0.

DOT 5.0 (first developed for aircraft) has a higher boiling point (also less compressability) than 3.0 or 4.0, but I think HD only used it because it's more expensive! (when they first started using it you had to buy from dealer) Also cannot be mixed w/3.0 or 4.0. (will work for a while then screw up entire system, usually clogging the master cyl.)

I haven't used dot 5.1 myself, but know about it. The problem is that you have to get the factory fluid out because it is not compatable with new 5.1. Because of this I still use OEM (5.0) fluid in American bikes with juicers!

I used to have DOS 5.0 in my computer does this mean that in the future I will need Vista brake fluid?

[flynrider]

DOT 5.0 (first developed for aircraft) has a higher boiling point (also less compressability) than 3.0 or 4.0, but I think HD only used it because it's more expensive! (when they first started using it you had to buy from dealer) Also cannot be mixed w/3.0 or 4.0. (will work for a while then screw up entire system, usually clogging the master cyl.)

DOT 3 & 4 are glycol based fluids. DOT 5 is silicone based. They're not chemically compatible and will really gum up the system if mixed.

I've never heard of DOT 5 being used for aircraft. All the ones I've ever worked on used MIL-H-5909 hydraulic fluid, which is petroleum based (and is also used in hydraulic landing gear struts, much like motorcycle forks).

[Sev]

It gets used in race bikes because they typically run at higher brake temperatures and the fact that it cannot absorb water means that it needs to be replaced more often to ensure you don't get the water pooling the calipers.

So around the japanese-bike shops it gets referred to as race fluid. And when it's put into a bike it usually happens in conjunction with replacing the lines and seals.

DOT5.1 is also glycol based and as such can be mixed with 3 or 4. It's said to boil at an even higher temperature then DOT5, but I have no proof of that yet.

At school there was a lot of... questioning as to why DOT5 was used for Harley's we suspect it has something to do with the fact that it is not as damaging to paint as DOT3 or DOT4.


Above and beyond that, most "modern" japanese bikes use DOT4. It's rare to find a bike that suggests only DOT3. And in all honesty there's no real reason not to switch from DOT3 to DOT4, unless you want to save some $$$.

[coffee_brake]

Brake fluid doesn't cost much. And the only tools you need to flush the lines are a bit of hose and a wrench and a can, (we use empty ketchup or salad dressing bottles--holds the tube in there). If your fluid needs to be topped off (you don't have a leak in the lines or calipers do you?!) you might as well flush the system.
ALSO once you open a can of brake fluid, it will rapidly go bad and collect moisture from the air. Like, in a couple weeks (as in my case). You'll pour it in there and see clear blobs in it that you couldn't see in the container but then it's too late, you'll REALLY have to bleed the entire system then.

I'd just flush the system now if it's tan-colored or low, or wait till you get the funds and do the whole thing then. Not expensive, and really, there's not much room for compromise on motorcycle brake maintenance.

[slimcolo]

US Army uses silicon brake fluid in everything, including aircraft. ( this has to do more with use-ability than preformance)

As stated by Sev and Flyinrider DOT 5.0 is silicon based and will not eat paint, or take on water but you'll never convince me that the ability to gouge prices was not a factor when HD started using it. A pint of this (motor Factory brand) costs $9 US and dot 4 is only $3.60. It is expensive and a lot harder to find. There are also dot 3 racing fluid (bp 550) and dot 4 racing (bp600)

Several years ago I mixed dot3 and dot5. After a few weeks it looks like molten lead. (had to replace brake light switch and brake pads and rebuild the wheel cyl. after about 6mo.)

[crazypj]

DOT 5.1 is glycol based same as 3&4.
DOT 5 silicon is evil stuff that rots out calipers after a couple of years (even with fluid changes) Any water vapour that gets into system will sink to lowest point. The bleed nipples are at higher point (to let air out) Unless you physically remove calipers/slave cylinders and clean them when you do a fluid change the water builds up and lowers boiling point to 212 deg F.
Its normally classed as race fluid because racers strip systems to examine them and the problem doesn't happen. The US military wanted DOT 5 to lower maintainance ( I bet they have a million or more vehicles to service) but they found maintainance is actually higher with DOT 5 than with 3, 4 or 5.1 Complete systems must be changed instead of changing fluid annually.
One other thing, If you switch o DOT 5 from 3,4,5.1 you can flush all lines wih alchol .
If you try and switch from DOT 5 back to Glycol base you HAVE to change all lines and seals as the silicon gets intpo he surfac