I need to top off my brake fluid but can't find any DOT 4 brake fluid in any local car store, so can I use DOT 3 instead?   Don't know what the original owner have on the bike so I wanna be conservative and make sure about it.  Please don't tell me to go ahead bleed the old one out and put in a new one in coz "mechanically"  im not there yet   again thanks all.

Auto zone, napa, Kragen... all have dot 4... No clue what it has so you on your own. BTW if its purpleish/bluish in color its dot 5...3 and 4 get brown with age, 5 stays blueish...
Cool.
Srinath.

As far as I'm aware certain fluids are incompatible with the seals used in a particular system, for that reason alone, I'd recommend using what is specified on your reservior (unless someone extremely qualified tells you otherwise).  DOT4 shouldn't be that hard to find, heck even Wal-Mart should have it, or any auto parts store.  

Even if you have to go to the dealership and get the rip-off genuine stuff, for something you only change out every year or six months you're not out that much...

i agree, sometimes they are compatible, then again, sometimes they are not. you could try it, but it might fubar your system and you'd be  :x  :x  :guns: . id stick w/ 4, most of the inconvenience stores only carry 3, but all auto parts places, dealers, and even wally-world will have it.  :mrgreen:  :mrgreen:  

I almost used DOT3 brake fluid, but I remember seeing somewhere to use ONLY DOT4 brake fluid. Not sure what is the difference, but I would not chance it. Go to your local motorcycle shop and get some. Inexpensive.

I'd use dot 4! thats what it calls for

One of the differences between DOT 3 and DOT 4 is the temperature at which they boil/vaporize.  DOT 4's boiling point is higher.  If there's one thing you don't want in your brake lines, it's easily-compressed gas!  (You want uncompressible liquid at all times.)

Since DOT 4 is called for, I wouldn't risk DOT 3.  You never know when you'll have to do the "emergency hard braking" thing!

Isn't Dot 5 supposed to be evironmentally safe? And, like not remove paint if you spill any?

I think DOT 5 is the kindler/gentler brake fluid.

I don't know what the other properties are so I just stick with what the manual calls for.  

As Kerry said, not all of the different brake fluids have the same physical properties.

Quote from: scratchIsn't Dot 5 supposed to be evironmentally safe? And, like not remove paint if you spill any?

The problem with DOT5 is that it can be the only thing in your brake system.  The guy at the speed shop said simply flushing wasn't enough.

The boiling point is higher in DOT 4 than DOT 3.  All the recent European cars that I saw at the shop required DOT 4.  We usually followed these "rules" at the shop
ok to add 4 to 3
not ok to add 3 into 4
never saw a car come in with 5 but its blue.  My friend is using it in his car (he replaced everything in his brakes... literally everything but the pedal)

With a higher boiling point, DOT4 will give you less brake fade in high braking situations

3 & 4 arnt far off chemicly speaking,  DO NOT add 5 to anything but 5, i was told it was silicone based and for all intents and purposes does not boil. but will chemicaly react to other fluids in a most negative manner.  i have drained my systems, rinsed with brake cleaner, and refilled with Dot 3, simply cuz i can get it anywhere, at a supermarket, parts shop, even local 7-11/quicky mart at 2 am should i need it. never had a problem with brake fluid boiling on me save once when i had a sticking caliper on a car that sat for years, but then hell, the flames where neat peeking out from slots in rim

perhaps on track where constant hard braking is the case, boiling may occur

Dot 5 is silicone based. Its environmentally better, does not remove paint, does not need to be used from a new bottle and does no absorb water. It also has higher boiling point and absorbs no moisture. Pretty much the super man of brake fluid. Further it lubricates the vacuum bleeding hand pump I use to do brakes. Also is colored blue. Add a Red S and its super man. OTOH it is harder to find, more $$$ and wont mix with 3/4. I have bled systems fully and used Dot 5 in my 89 GS for over 5 years. No adverse effects what so ever. Also used it in other Jap bikes made in 82-92. No issues in any of them across manyfacturers. I have heard the old brit bikes needed the petro by products to keep themselves pliable.
To mix with pre-existing brake fluid especially if you dont know what it is Dot 3 or 4 use Dot 5.1. Same handling cautions as 3 or 4, and probably as pricey as 5 and harder to find (but try harley shops) but will work if you mix numbers.
If I were you... I'd buy the beelding pump and suck out the whole old fluid and put in 5. But That's just me.
Cool.
Srinath.