Brake Fluid Question

What would a restorer likely to use for brake fluid? Are a Dot 3 and Dot 4 compatible? Is there a way of determining which I have? Thanks in advance, KK

i would think a restorer would use dot 5 to protect the paint.

If he didn't use DOT 5, I wouldn't go there. I've seen thousands of dollars in paint damage saving a few bucks on brake fluid.

Good article on Dot 3 and Dot 4 fluids.
https://www.autozone.com/diy/brakes/dot-3-vs-dot-4-brake-fluid
I also like to use Dot 5 on restorations, not only because of protecting the paint, but Dot 5 does not draw moisture like other brake fluids. Seen it many times, car is restored and then stored for several years, owners sells or wants to drive it and brakes are junk leaking fluid. Read the article Dot 4 draws moisture even more than Dot 3.

Moisture still can get in the system and dot 5 doesn’t absorb it, then the moisture can cause corrosion.I just flush every few yrs.

Good point and suggestion.

To figure out what is currently in the system, scoop a little bit out of the master cylinder, and dump it into a clear jar with a quantity of DOT 3 in it. Then shake it up and let it sit until the next day. If your system has Dot 5, they will separate. If it has dot 3 or dot 4, they will stay blended.

I have been using Dot 5 in all of my collector cars and race cars for 40 years. I have put cars into storage for over 20 years, and pulled them out and they still had a perfectly working hydraulic brake system using Dot 5. I would never put anything else into my cars now.

I've just restored my Demon and used Dot 5 for the first time. Everything works great and would definitely recommend it.
If it's a sealed system, how would moisture get into it?
Not being a wise guy, I promise.....If it can get in, I won't take a chance and flush it every few years also.

Thank you!

From research I did air gets in microscope pores in seals, hoses & m/c cover. Had stainless steel brakes rebuild a pair of calipers off a super bee I had. Tag on calipers said not to use silicone brake fluid.

[quote=rickraw]From research I did air gets in microscope pores in seals, hoses & m/c cover. Had stainless steel brakes rebuild a pair of calipers off a super bee I had. Tag on calipers said not to use silicone brake fluid. [/quot

I'd use DOT 5 anyways.................but that is me.

I was in a very similar circumstance back in 02 I bought a set of wilwood calipers and their instructions said not to use Dot 5. They even had a big red tag hanging off of each caliper that said not to use 5. I did anyway. Now 20 years later zero problems with those calipers. And Wilwood changed their mind and now they sell their own dot 5 fluid.

The thing is dot 3 and Dot 4 attract moisture. It gets sucked in past the seals in any place else it can because the fluid draws it towards it.
Dot 5 does not attract moisture. It's neutral. There's no attraction, so moisture doesn't go into it. I never flush mine. And I live in a very moist climate, plus freeze and thaw, frost, and condensation. I've never had a cylinder corrode or leak even after 40 years with the same dot 5 fluid in it.