Life without DOT 4 brake fluid?

[tt_four]

I was all hyped up to change the brake fluid in my GS after one of my friends had me work on his mountain bike and needed the brakes bled. In general I hate hydraulic brakes, but regardless the process was fresh in my mind so I figured I'd do mine before I forgot how to do it. Looking around the places near me I'm having a hard time finding DOT 4 brake fluid. Both places I've looked have DOT 3 and DOT 5, but neither have DOT 4. One store had a bottle of DOT 3&4 and another store had a bottle of DOT 4&5. So either of the last two seem like they would work. They both say they should work for DOT 4. From reading other posts on here I've seen that you can use DOT 5 without a problem, but that you need to flush your system really well before you put the new fluid in it, so my main question is if I use the brake fluid that says it's for DOT 4&5 as a replacement for the DOT 4 that's in my bike now, can I just replace it and go on with life, or do I need to worry about the partial amount of DOT 5 that's in there and run new fluid through several times??

[ineedanap]

Brake fluid can get confusing but here's how it works.  There are 4 different "grades".  They are 3, 4, 5, and 5.1.  

Dot 3, 4, and 5.1 are all compatable.  They're all polyethylene glycol based.  The only real difference is the boiling point.  The higher the number the higher the boiling point.  You can mix all three together as much as you want.

Dot 5 is the oddball.  Dot 5 is silicone based and is not compatable with anything else.  You can not mix this with any of the other three without bad things happening.

store had a bottle of DOT 3&4

That bottle was dot 4.  They just say 3 and 4 because it meets both standards.  

and another store had a bottle of DOT 4&5.

Are you sure it didn't say meets 4 and 5.1 standards?  I'm guessing the second bottle was probably 5.1, which meets 3, 4, and 5.1 standards.  It is sometimes called super 4 to add to the confusion.  

[joshr08]

This should be put in the FAQ area because this is something very useful now and down the road. nappy

[tialloydragon]

what happens when you mix incompatible brake fluids?  I have no intentions of doing so, but all I have ever heard is that "bad things happen."

[tt_four]

Hmm... I can't remember which of the two I bought, and which one was the one I just saw at the store by my work. I'll try to remember to check in the morning before I leave for work, so if I bought the 4/5 version I can take it back and pick up the 3/4 to be safe. I don't remember there being a .1, but I had no idea there was a 5.1, so I wouldn't have noticed anyway.

Thanks

[black and silver twin]

what happens when you mix incompatible brake fluids?  I have no intentions of doing so, but all I have ever heard is that "bad things happen."

They form a goopy substance that blocks fluid/pressure travel through the lines. so potentially no brakes or at least crappy brakes that drag

[tt_four]

I checked and I picked up the DOT 3&4 fluid, so I'll just try it out and see how it goes.