I am resending this post as I made a typo in the last post regarding DOT3/4. DOT3/4 melts paint, DOT 5 does not. I corrected it below, sorry about any confusion. Bob
The brake fluid topic has been discussed often and with fervor on this list. You basically have two choices for fluid, DOT 3 & 4 that are hygroscopic, that is, they have an affinity to absorb moisture, meaning the fluid needs to be flushed and refilled every 2-5 years. This is necessary to keep the internal parts of the system corrosion free and maintain a high boiling point. Note that DOT 3 & 4 will damage paint.
The second type is DOT 5 silicone fluid which is non-hygroscopic otherwise known as hydrophobic, meaning it does not absorb or mix with water. It also has a higher boiling point and does not melt paint as does DOT 3 & 4.
You will find many opinions on this subject, depending on the car, how it is used, and even where it is stored. My personal experience is that I have had silicone fluid in my 300G since 1978 and have had excellent results. I have gone as long as 18 years without bleeding the system or needing to do any brake work. Having written that, I am now flushing (bleeding) my brakes about every 8-10 years to keep the fluid clear and clean.
Regarding the 18-year period mentioned above, what prompted me to inspect the system was pulling toward the left when braking. I removed the front drums and found the lower left wheel cylinder leaking. Upon tear down and inspection, I found moisture had gotten into the system over the years and rested in the lowest point, causing corrosion. I removed the cylinders, had them sleeved with bronze, rebuilt them and restored the system with DOT 5.
So, my personal experience is that you can go much longer between system flushing with silicone fluid, but it still should be done, especially on our single circuit brake systems. I have talked to list members that converted to silicone fluid in the late '70s and never flushed the system citing no reason to do so. If you do convert from DOT 3/4 to DOT 5 it is prudent to also change out the rubber brake parts and hoses, and thoroughly flush the system of old fluid. Note that DOT 5.1 is not silicone fluid and is hygroscopic like DOT 3/4, but I have had no personal experience with DOT 5.1 and can't offer any comment on its suitability for our cars.
300G convert owner since January 1978
331 La Questa Dr
Danville CA. 94526
I remember reading a post about brake fluid recently (in our news group) but I can't seem to find it now. it was in reference to different types of fluid and I think I remember reading about a non hydroscopic fluid club members had been using. Ring a bell anyone?
Posted by: "Bob Jasinski" <rpjasin@xxxxxxxxxxx>
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