The Stovebolt Site Forums The Shop Area Driveline Brake Fluid Survey

I'd like to hear some opinions about brake fluid. DOT-3 or DOT-4 versa the silicone type DOT-5. Which would you choose and why?

I'd like to use the DOT-5 type due to it resisting water getting into the system, however, from what I've read it requires silicone compatible rubber parts in the system. If I go this route where does one buy the silicone tolerant parts/kits? Maybe it's just over kill, right? Anyone?

I stuck with dot 3 in my 52 only because I never had a problem with it and if you got stuck some where it's easier to fix,do not need anything special.

Pete

I agree with Pete Dave, unless you’re running high speeds and disc brakes on that '46 I leave well enough alone. If moisture absorbs ion is a concern then I'd just flush it with fresh fluid every couple of years, which isn't a bad idea in any case.
Denny Graham
Sandwich, IL

Dot 3. I had a bad experience with Dot 5 destroying wheel cylinder cups.

I read somewhere that most brake fluid marked DOT-3 actually meets the DOT-4 standards, but is marketed as DOT-3 because that is what people are used to buying.

Nothing I've read has convinced me that DOT-5 is worth the hassles in a street driven car or truck.

At the risk of start another silicone/DOT3&4 debate, Silicone DOT 5 won't entirely prevent moisture from getting in. Moisture (water) is not soluble in silicone so any that gets in doesn't dissolve in the fluid but will usually sit around as little drops on the surfaces. If that little drop gets in the right hot place then the boiling point becomes 212 deg F. So you have to have a system that is completely and totally sealed. The advantage of the glycol based fluids is that any moisture that gets in dissolves in the fluid and lowers it's boiling point but it will never down get to 212 deg F since there will never be any pure water present.

One other caution regarding dot 5, you do not want to use it in a vacuum boosted power brake assembly that gets it's vacuum from the intake manifold.
That silicone will become abrasive if it gets sucked into your motor and gets hot.
Plus, silicone leaves a weird film on everything it touches and is extremely hard to wash off.
Something to consider if you plan on painting.

Ray

If you use DOT3 and flush the system annually like you are supposed to, you won't have any trouble. Don't spill it on paint, because it removes paint.

This topic has been beaten to death way too many times.

Dot 5 is for race cars and motorcycles and is really not worth the extra cost and effort if you properly service your brake system with a yearly flush. Plus finding street car / street truck brake parts that are compatible will be difficult.

Steve, you are correct, most of the new brake fluid is DOT3 / DOT4

crenwelge,

Why would anyone want to flush their brake system annually? I've never heard of such a thing. I've had many vehicles and have never flushed the brake fluid ever. Can you explain?

I agree, yearly may be recommended by somebody somewhere but I bet there aren't more than a handful of people that actually do it. Mine gets flushed every time I do the brakes which is five to seven years.

Actually, the "somebody" is the manufacturer. The service interval is listed in both the shop manual and the owners manual. It's not as critical with newer cars with sealed systems, but with the vented systems that the older vehicles use, it should be flushed annually as the manual states.

I've been running Dot 5 Silicone brake fluid in my 37 pickup since the early 80's (when is was cheap to buy) without any problem. I recently installed a new rear end in the truck, a dual master cylinder and replaced some older brake lines, like the originals, and am a very Happy Camper. No trouble what so ever.
So, I recommend Dot 5, and if you think you will get stuck on the road needing some, they have loads of the stuff at any Harley house.

If moisture is a concern a better solution is to install a modern master cylinder with a sealed cap and a reservoir large enough to hold enough fluid to compensate for pad or lining wear. Then never open it to "top it off".

Not sure if annually was posted but I said every couple of years. The glycol based brake fluid is hydroscopic, i.e. will absorb moisture from the air. This will cause rust to form on the steel parts that it contacts. Often seen in the bottom of the wheel cylinders where it settles often.
I think reading back that Ken might be referring to the trucks that he runs in his business, which are probably driven many miles each year. Most of the older systems are vented and every time you apply the brake there is air sucked into the master cylinder to displace the fluid that has moved into the system. The more times you apply the brake the more times the fluid reservoir is exposed to fresh moisture laden air.
Denny Graham
Sandwich, IL

Denny! suprised at you! hygroscopic is the word

Bill

I've used silicone fluid in my '37 since I rebuilt it in '99 with out any problems. It stops just fine. Joe

Denny is right in saying it depends on how much you use the brakes. Back when we actually used the vehicles, we flushed the system annually. Sometimes that wasn't often enough. Water causes rust. Rust makes a rough spot in the wheel cylinder which causes a leak. Pulling a hub on a 3/4 or larger isn't much fun. Flushing the system is easier. I have gotten lax because I don't drive any one of my jalopies much. But I would think that most people who have only one classic vehicle would maintain them. With a pressure bleeder, its not even as dirty a job as changing oil.

I'm running DOT-5 in my '52. No problem finding it. They have a shelf full of it at my local NAPA store. It's a little pricey though.

Oh, and no problems with performance either.

a lot of people never change their auto trans fluid or power steering fluid, either....:-o

Yep, so I use 3/4

Grigg

When I put all new brake system parts in my 54 Suburban, I used DOT-5 (after checking with rubber-hose, wheel-cylinder, and master-cylinder vendors about compatibility). It works fine and has had no problems (except for a dirty/oily/greasey interior of the new master cylinder that was incompatible with the DOT-5 fluid).

The 54 pickup that I am restoring will also have all new brake system parts but it will get DOT-3/DOT-4 brake fluid. I figure why waste the money, why worry about compatibility with rubber parts, and why worry about silicone contamination in my garage (where I paint). I will take 30 minutes a year to bleed the system when I change oil/filter (in the fall, before winter hibernation).

I put all new brake parts in my 1954 GMC 100, checked this scenario out and found dot 3/4 was good enough to last 50 yrs, so I guess it will be fine in mine, I don't think I will live to be 130 yrs. old so let the next guy worry about it. I do use dot 5 in my Harley and it is expensive.

I use DOT 3/4 SYNTHETIC.

Luc :the military uses dot5 on there equipment.I use it on my 51 now for 11 years.It's silicone base .DONOT mix with 3 or4 dot.No mosture in break lines setting a long time.no rust.Dot5