VCCA Home Forums TECHNICAL - 1945 AND NEWER 1949-1954 50-BRAKE FLUID- WHAT TO USE

my 50 has the original huck brakes i have kept the car original started her up today checking all fluids got to brakes and cant remember what to use.my notes say DOT3 is okay DOT4 is better i have an almost full bottle of DOT3 SYNTHETIC that i bought i dont know if i topped the master cylinder with this last year or not i think i did but not sure question is can i use that in my system or do i have to straight DOT3 OR DOT4 if available i think thats how i ended up with the synthetic the other is not sold at my parts store need to go for a long ride without a mask this quarantine is driving me nuts thanks

Well, what other vehicle would you have used the DOT3 SYNTHETIC in? If the 1950 with the Huck brakes is the only vehicle you remember putting brake fluid in, then go ahead and put some more in! DOT3 is all I have used in my 1950 Chevrolets for the past 49 years!

DOT3 or 4 are both fine. Separate or combined. Just different boiling points. Ideally you really should only use fresh fluid from a sealed bottle as it will absorb moisture from the air that's why it's recommended to change the fluid every 2 or 3 years if you can...

you are both right synthetic dot 3 is what to use i hate when i have these senior moments so now all have to do is find the bottle of brake fluid i put away so i wouldnt misplace it thanks guys

What is synthetic dot 3? All components in Dot 3 brake fluid are and always have been synthetic or manufactured.

I would not recommend mixing Dot 3 and Dot 4 brake fluids. Don't remember if we ever tried mixtures of them on the specification tests. Swelling of natural rubber is one of the most important tests. If the natural rubber cups either swell or shrink your brakes could fail.

US produced new cars are fillled with Dot 3. Dot 4 has a higher boiling point but also attracts more water.

What's everyone's opinion of DOT 5 silicone brake fluid other than the higher price? Heard it doesn't attract water like 3 & 4 so shouldn't need changed near as often. Is that correct ?

Dick

Don't use DOT 5 if your brake components are original. The silicone fluid is not kind to the older rubber. Also do not mix DOT 5 and DOT 3 or 4. If you are going to use DOT 5 you should completely drain all of the older fluid . If not it could cause clogging and swelling of some of the seals.

This is what I have found when checking on changing to silicone fluid. Might want to do some research.

Hope this helps, Pete

Did not realize DOT 3 and 4 could not be mixed. Scared me for a minute.

I've always used them interchangeably based on availability but when I thought about it I always do a full change/flush with EITHER Dot 3 or 4 but have not been in a position of just "topping up" and adding new fluid to existing which could lead to mixing if you don't know what fluid is in there.

DOT 5 is unique. It's silicone based so doesn't absorb water. It can sometimes react with rubber seals and it's unpredictable which ones. Some guys have great luck with it but the whole brake system needs to be 100% new or else flushed with alcohol to remove all of the previous types of brake fluids. Like all fluids it still should be changed but can go a bit longer.

There is also a DOT 5.1 which I believe falls under the DOT 3 or 4 family but has a higher boiling point than both.

Edit: add link to Wikipedia. Not a huge fan of wikipedia but the basic summary is useful here.
https://en.wikipedia.org/wiki/Brake_fluid

The wikipedia article is an accurate summary of brake fluids. There are a couple of statements that I might have to do some research on to be fully comfortable, I was part of a group that developed DOT 4 and DOT 5 fluids back in the early 1970s.

Using silicone brake fluid (DOT 5) is fine ONLY IF you have cleaned all the lines with alcohol first. You MUST replace all the rubber parts like the wheel cylinder boots and the rubber flex hoses that connect to the wheel cylinders. Any rubber connections in the system MUST also be changed. They will be contaminated with the regular fluid. If you don't, you might get two years of service out of all you hard work. Ask me how I know that! If you do end up using silicone fluid, you must pour it into the master cylinder VERY slowly. Tiny bubbles can form and it will take a long time to bleed them out. About 8 years ago, my 87 year old mechanic used the silicone fluid on my 1934 Chrysler. Knock on wood, I have not had a single issue with those brakes. I also am using it in my 1950. It's more work and more money but I think more dependable. Mark the master cylinder with a tag stating what's in it.

Wikipedia says US cars use Dot 4. This is not correct, they use Dot 3...see your owners manual. "Import" cars use Dot 4, That is why they recommend changing the fluid every two years.

I also have mixed Dot 3 and Dot 4 in my cars and never had a problem.

As Gene implies, Dot 3 is just fine. No need to overthink this.

Best,

Charlie

Interesting discussion. Right up there with "what engine oil" or "what gear lube".

Like Charlie says, don't overthink this.

I thought I would add this to help confuse the issue. On the other hand it keeps my life simple. This is what I have been using for the last 20 years. I will add it to any car that is in my shop if needed.

Silicone brake fluid can kill some hydraulic stop light switches,I think Ron Francis sells the good ones.

....or install a mechanical switch like the older Chev used.

Dick