DOT3 Brake Fluid

[rboltz]

As soon as the weather warms up, I'm going to finish my brake project and put in the dual master cylinder. I replaced all the wheel cylinders with the Ford ones soon after I got the truck. I also put in a few feet of new brake line and all new hoses. I kept the DOT3.

Now, after I put in the new master and replace the remaining lines, should I put in DOT5? If so, what about the residual DOT3 that is coating the wheel cylinders and lines? I intend to flush the old fluid out as we bleed the new system but some will surely remain unless I replace everything again.

[Hammer]

Do you want to use the silicone just to have the same thing in all MVs?
Or was there another reason to use it?

Best way is to replace everything, of course.
But a flush should get enough out for all intensive purposes.

[randyscycle]

If you want to switch to DOT5 you will need to flush out the remaining DOT3 thoroughly.

Use denatured alcohol to flush the system. I rigged up a small electric fuel pump, and used it to pump the alcohol through the system from the master cylinder lines then went to each wheel and bled out the fluid until it ran clear with alcohol. Then I left the screws all open for a bit so that the alcohol could drain/evaporate, then followed with fresh DOT5.

[rboltz]

Do you want to use the silicone just to have the same thing in all MVs?
Or was there another reason to use it?

I don't know. Just following advice from archived posts. I understood the DOT5 would not retain moisture, a killer of lines and cylinders. If this is not the case, I won't bother.

[Hammer]

Honestly, if you actually change/flush your brake fluid on a 'somewhat' regular basis, this really isn't a needed thing.

MVs are normally left alone for long periods of time. And regular brake fluid will absorb water, by design.
Thing is, if you change your fluid every couple years, the regular brake fluid is actually better for you, as it will hold the water in suspension, and make flushing it out easier.

Silicone is nice for certain reasons, but for most people, the effort and cost just isn't worth it.

[Hammer]

Oh yeah, no retain, or absorb moisture. This is true, but the water that gets in a system will actually pool up in spots, which can actually rust certain spots FASTER.
Not often that it happens like that though. As it doesn't absorb moisture from the air like normal fluid does, but for super wet usage, it can happen.

[kwai]

I run DOT5 in my trucks. Because the DOT5 doesn't absorb water, the lines and cylinders should last much longer. DOT5 also has a higher boiling point so won't boil away as quickly when the brakes get hot. Good for high speed racing which the M715 doesn't do.

[george walker]

dot 4 is an alternative, its got a higher boiling point and its compatable w/ dot3 and priced similar. you can always do a search online of these types of fluid and see what info comes up.

[Hammer]

DOT5 is also prone to entrained air bubbles. Which can actually make it boil at a lot lower temp. Which makes more air bubbles.

Not typically a problem, but it means you really need to have the system completely bled.
Btw, look at the boil point on different fluids.
You can actually find DOT3 with HIGHER boiling points then some DOT4 fluids!
The DOT standard is only for a minimum set of standards. After that, anything is possible.