Brake Fluid

Not open for further replies.
Sep 19, 2005
I have a 1973 850 Commando that was stored with the brake resevoir empty. What Dot number brake fluid should I use? An old service manual lists Lockheed 329 hydraulic fluid but I don't have a clue as to what that is equivalent to. Sorry if this is repeat basic information, but I couldn't find it in a search for "brake fluid" on old posts.
Thanks, Jim
Dot 4 Lockheed is fine but do not use Synthetic brake fluids. This will deteriorate the rubber seals in your mastercylinder, flex hose and the seals in your caliper.
Interesting comment regarding Synthetic brake fluids ~ I have not heard this before.

I have been running Silicone Brake fluid since 1993 in my 850.. you think I am about to experience a brake failure? :shock:
This is an area of rather heated debate -- some people advocate silicone (DOT 5), others recommend glycol-based (DOT 3, 4, and 5.1). Glycol and silicone are not miscible (can't be mixed), so do not use one if the other is already present. Original equipment would have been gycol-based fluid, so the odds are enormous that that's what you've got in there now. DOT 3, 4, and 5.1 are completely miscible with each other, but I would not recommend you use anything less than DOT 4. The most recommended DOT 4 is Castrol LMA. I think the DOT 5.1 is Valvoline Syntech or something like that, but I've never used it. It's supposed to have most of the benefits of silicone without the drawback of having to completely flush the system of all the old fluid first. Unlike silicone (and like all glycol-based fluids) it will damage paint, so clean up spills immediately.

Taken from a MGB site. :wink:
What is this bologna about the silicon rotting seals?

I have been using Silicon 5 from Harley Davidson for over ten years and since I changed to Silicon, is the first time the seals have not needed to be replaced every year or so. Over ten years and still not a drop. If you saw my tank...and the hundreds of holes in the paint from the old type brake fluid....which blew out of the nice leaky seals and sprayed over the entire'd not think twice about what to choose. I still run the original seals in the calipers too...come to think of it, and they don't leak either.

In 83 I had to resray my tank after the seals went on the master cylider, I replaced all the seals and put silicon brake fluid in, 22 years later those seals are still there and working 100%.

At least you got to spray the tank new...mine looks like it has chicken pox. Glad someone more nasty normal fluid for my baby...only the good stuff. :lol:
Ten-Four gentlemen.....the silicone DOT 5 is marginally less lubricative than the glycol based DOT 4 and 3. But the silicone is very much less hygrosopic than the glycol. Rust kills more brake systems than wear and tear. Plus the silicone doesn't attack paint. If the bike has been sitting for a long time, you need to disassemble the components and rebuild them to be safe, anyway. Use that opportunity to remove the glycol and install the new parts with silicone fluid. Fear not the future, good stuff abounds.
I have rebuilt master cyl & caliper, new ss brake hose ready to install. Have read that DOT 5 can give a slightly spongy feel & fluid pressure brakelight failure sometimes mainly in old cars. Anyone experience this on a Commando?
Not open for further replies.