DOT 4 vs DOT 3 fluid?

[slownugly007]

I bought a used front master cylinder off an 89 ZX10 and Im in the process of installing the rebuild kit, the MC says to only use DOT4. I dont have a problem running DOT4 in the system since I have rebuilt the front calipers and cleaned out all the DOT3, plus Ive got new lines on the way.

My question is what are the advantages of one compared to the other, if any? And if I decided to run DOT3 can I run it in the newly rebuilt master cylinder (new seals, piston, spring and Ive cleaned it withs parts cleaner and rinsed it out)

[MarkPBG]

DOT3 and DOT4 fluids are compatible, but the DOT4 is preferred because it has both a higher "dry" boiling point (before moisture inevitably works its way into the fluid) and a higher "wet" boiling point (after the inevitable water absorption has occurred). Also, DOT 4 is more resistant to water absorption. It will still absorb water, but it will take longer. There are other fluids you can use too, but the (relatively low) performance characteristics of the CB750 braking system make the extra expense wasteful.

You can use DOT 3, but if you have access to it, it's better to use DOT4. :)

[Piute]

  Your parts cleaner may not be compatible with any brake fluids,Myself I was told by Paul(mechanic)to use rubbing alcohol (1.25 Wally world)worked great So far using DOT 4 myself due to the fact Paul stated that it absorbs less moisture from the air.water is your enemy in this bit.I had went through all/most same changes as you,But it still eats paint ,,Mine (alcohol)came in squeezz bottle and anytime fluid got on paint sqeezzed (shot)it with alcohol then wiped easy with soked rag.
                                     GOOD LUCK

[slownugly007]

awesome thanks mark! Thats what Ive been reading but just wanted to run it by the guys on here since they havent lead me astray....YET!!!  JUST KIDDING! So it wont hurt it to lube the new seals with DOT3 if I decide to run DOT4?

[MarkPBG]

These guys know more than I do.....they'll get the right answer for you.

Whatever fluid you use to lube the seals however, should be the fluid you fill the system with. Mixing of types, even compatible types, is not recommended. That's just a "this will get you home" measure when your fluid is low....and they DO recommend a flush and fluid change if you ever need to mix them on the road to get home. Mixing fluids and leaving them mixed long term is not a good idea. ( i'm assuming that doing so might result in a fluid mix thats maybe more hydroscopic and/or may even have a lower boiling point than either one alone, but I don't know)