The Stovebolt Site Forums The Shop Area Engine Shop Suggested brake fluid

Getting ready to install my new brake system (new SS lines and cylinders). What is the suggested brake fluid? Whats the difference between Dot 3, 4 and 5?

DOT3 (&4) are glycol-based, while DOT5 is silicone-based.

In theory, DOT5 is superior to anything else as it has a higher boiling point and doesn't attract moisture, but for the life of me I have never had luck with the stuff. It seems to hold air which leads to spongy brakes and your system has to be totally rid of the old fluid as the two aren't compatible.

Valvoline Synpower makes a DOT4 that I can recommend. I wasn't satisfied with the brake performance in my '51, so I flushed out the DOT5 and replaced it with the Synpower DOT4 and all my problems went away.

If it's a daily driver, go with dot4. If it's only driven to church (I know how often most of us go) use dot5.

Because of the high quality of restoration you are doing to your truck, Craig, I highly recommend DOT 5 Silicone. If you use regular Dot 3 or 4, you will put all of your paint restoration work at risk. Dot 3 or 4 will destroy your paint work no matter how careful you try to be. Dot 5 Silicone will not phase your paint work and be your best choice for all the other reasons. The only thing about Dot 5 that I have found to be a problem is leakage. It is so thin and slick that if your are going to have a leak in your system, it will show up with Dot 5 Silicone. Since you are totally rebuilding your system, that may not be a problem for you. I would take that chance.
As far as bleeding the air pockets out of it - yes, it does take longer to do that, but you can get them out. Patcience is the key! I know you have patience by what I see you are doing to your truck!
I have had it in my 37 since 1980 and have enjoyed all of the positive aspects of Dot 5 Silicone.
One last comment - it is expensive with a quart going for about $30.00.

If you are starting out with clean lines and cylinders, use Dot 5.

I use it in my '54 3100, works fine.

For those with original (vintage) master cylinders, DOT3. The newer stuff can harm the older rubber seals and cause leaks.

-Boyo

I use DOT3 or DOT4. Dot 4 is more hydroscopic than Dot3 (attracts water easier) but has a higher boiling point. Both Dot3 and dot 4 have a significantly lower boiling point when they are saturated with water, and should be changed annually since the stovebolt system is an open system. A system with a more modern master cylinder with a bellows breather can handle changes every two years. I change my fluid every 3 times I adjust the Hucks. Always change fluid anytime you open the system. I change it by cracking the far bleeder and topping it off as it bleeds down, and then re-bleed all four corners until it runs clear. That gets 99% of the water and crud out.

When I rebuilt my brake system I used Dot 5 and had trbl with leaks. I flushed out the Dot 5 and replaced it with Dot 3 and had no trbl. with leaks since.