O/T Brake Fluid: DOT 3 vs. Synthetic

I'm finally getting around to overhauling the brakes on my 1965 IHC 1-ton 4x4. The lines and hoses are good from the previous owner, but the master and front wheel cylinders are shot with rust and corrosion, and DOT 3 fluid leaking all over. The rear wheel cylinders are still decent. I am sending the master and front cylinders to a shop in Minneapolis to have them rebuilt and have stainless steel sleeves installed. After I put everything back on the truck, I want to flush the lines, hoses, and rear cylinders and fill the system with synthetic fluid instead. I've never used synthetic, but I've heard from others that it will solve a lot of the rust and "water attraction" problem that DOT 3 fluid is known for, and the whole brake system with last longer and maybe save some lives. Is synthetic the way to go with this brake job? If so, is it critical to get every last drop of DOT 3 out of the system before filling with synthetic?

Dave,

We have used the $$$ silicon brake fluid in one of our late 60's Loadstars. It is not the ultimate fix for brake problems. It seems to have a desire to creep past the wheel cylinder seals, and so there is no pedal when we first try the brakes. So back to bleeding. As you may know, brake bleeding is much easier on the 1 ton than the Loadstar (with 2 cylinders for each wheel, at top and bottom). The rubber products (cups, etc) are made for the DOT 3 chemistry, and thus seal better.

In our cold winter temps, the silicon BF does not flow like DOT 3, so the brakes have a real slow response time.

There is NO compatibility between DOT 3 and silicon fluid. The brake system must be totally drained, purged with compressed air and then flushed with alcohol, and blown down again.

DOT 3 has its problems too. It is very hydroscopic, drawing in water and creating rust. So my solution is to use DOT 3 (much cheaper) and flush it from the system by bleeding all 4 brakes about every 2nd year. With this method, I have some trucks with over 25 years since needing new brake cylinders (or maybe an occasional one has been replaced in that same time period). Our most common problems with brakes is the rusting through of the steel brake lines, mostly from the outside as snow, ice, and road salt hangs onto the steel lines.

Maybe you'd get a better answer about the silicon BF from a local car or truck restorer's club. At least they would know much better how it works in your climate.

I also have a 65 IH 1 ton 4X4 with SRW and a 9 ft narrow box. I hope to bring it back to life, but I need a cab...it is just too far gone.

Good Luck with yours!

Paul in MN

Paul is right the problems are not worth the effort or results. Stay with dot 3 and cehck it every year or so.. Paul give me a e-mail phone number have a fellow wanting to sell me a 64 i ton 4X4 that should have a great southern cab.
Have only look at it from the road but it looked good. I collect IH but just did not need the cab. Jerry

Part of the problem with using DOT 5 fluid is that it is not hydroscopic. Any moisture that gets into the system will settle to the bottom. All the bleeders are on top to remove air. Any moisture will collect and rust the cylinders.

its been my experience that theres no magic cure...go thru your brakes completely when they need pads or shoes and you'll stay ahead of the moisture problems...vehicles and equiptment that dont get used much are the worst to keep brakes on.

DOT 3 is just fine for this ole binder. If you want, DOT 4 is somewhat better for water absorbsion
and has a higher boiling point.

DOT 4 is what all RV's get from me when doing brakes.

I have a truck with DOT 5 in it. I asked the auto part guy what different about this kind and he said it stops moisture from getting into the system., I just looked at the quart and it says Absorbes water- NO boiling point- 550 degrees
price, $19.99 a quart.. Steep. But the truck was a goverment truck, so you know they had all sorts of money to throw at it.

I'd say use the DOT5 if you're planning on racing or something else that will require the high temperature capabilities of it. But it sure as heck doesn't make sense to use it on a street vehicle. It's immiscible with water, so as another poster says, the water settles out. Racers don't worry about that, since they're going to completely purge their lines at least annually during the off season, and probably several times during the season. And if your seals have been exposed to DOT3, they need to be replaced as well, or they'll turn into a gummy mess when the absorbed DOT3 reacts with the DOT5.

I got my silicone fluid from Mesgeon (sp?)Brake out of Michigan. Wasn't near as high priced as local stores.
I put it in the 1981 F350 and have had no problems. Didn't get real fussy about cleaning out the old either. I thought mine said you can mix it ?? but not for use in anti lock systems.
I just had alot of it apart and drained and then refilled with the silicone and bleed until I saw the good clean purple fluid. I did the 1983 K10 chevy but it is gone now. so is the 1967 chevelle I put it in.
It won't harm paint either. Antique cars guys usually recommend it.

I would stay away from the silicon fluid. Many years ago I thought it was the greatest thing when I put it in my 1939 Ford. I had nothing but problems. It swelled up the rubber inside of the master cylinder so that the piston would not return back when I let off the brake. I think that it also screwed up a couple of brake light switches. I switched back and it is OK now.

You say the lines and hoses are good on that 1965 truck?
Did the previous owner replace them? In the last 20 years I have burst 2 front brake hoses. One was on a '65 chevy, the other on a 1986 GMC. NO FUN! Now I try to replace them every 10 years or so.

Its your truck, but I would stick to the Dot3. That is what the seals and hoses were designed for.