The Stovebolt Site Forums The Shop Area Driveline DOT 3 Brake Fluid

I have always used DOT 3 brake fluid in my 47 Chevy with an original type brake system. Components were all replaced with new around 2008. I eventually noticed that the brake fluid bottle says "synthetic". Having asked Dr. Google about this, the recurring theme seems to indicate that since DOT 3, 4 and 5.1 (NOT DOT 5) are polyethylene glycol based, which is noted elsewhere to be a "synthesized" compound, the upshot appears to be that ALL DOT 3 is "synthetic". Further, the appearance of the word "synthetic" on the bottles in the last 15 or so years may just be a bit of labeling eye candy.

Looking for a knowledgeable source to weigh in on 2 questions: Is there such a thing as conventional vs synthetic DOT 3 brake fluid?

On a side note, I moved the question here from a facebook group, having gotten everything from irrelevant to just stupid responses. Lesson learned :-D

Just like oil, brake fluid is "conventional" and "synthetic".

It all starts as polyethylene glycol but synthetic brake fluid undergoes a further process (just like synthetic oil) to make the molecules more uniform and consistent.

Additional reading on the matter doesn't lead to any definitive answers, mainly because the discussions tend to compare products throughout the range of brake fluids, from mineral oil to DOT 5.1.

So, I'll drill right to the underlying point. I have had increasing wheel cylinder leakage on my truck. I more suspect that this is a combination of age - the wheel cylinders were new in 2008 - and disuse. I drive it fairly regularly, but not for long nor very far. In the winter it will sit for more than a month at a time without being driven. The rest of the year maybe two or even three weeks occasionally.

The question about synthetic vs conventional DOT 3, if such a distinction exists chemically, is whether synthetic DOT 3 contributed to, or even caused, wheel cylinder leakage. Three noteworthy mentions are that I have never used any fluid but DOT 3, there is very little wear & tear on the wheel cylinders with 5k on the clock since they were new, and that the brake fluid has been completely flushed and rebled at least a couple times since.

I seriously doubt the synthetic DOT 3 caused any damage. It's basically the same stuff just "better".

I think you hit the nail on the head with the following:

1: Wheel cylinders are 15 years old
2: Truck sits around for months in the winter and weeks in the summer without being used.
3: When it is used, it's not getting a real workout.

Vehicles don't like sitting around. Rust and corrosion forms, rubber dries out, etc. I'd either rebuild your existing wheel cylinders or install new ones.

I concur. I doubt corrosion, but I don't doubt hardened/shrunken seals. I have a dual MC kit waiting to get installed. Plus I already have 2 new wheel cylinders, so I'll either rebuild or replace all. Thanks

My first job out of graduate school in the 70's was at a plant that had a large share of the aftermarket brake fluids. All the brake fluids at that time were synthetic. We only sold in bulk but I don't recall them being labelled "synthetic" then.