I'm replacing the entire brake system in my '64 Valiant, including all cylinders, solid lines and flexible hoses, so if there was a good reason, it would be a good time to change brake fluid as well.

What grade/type of brake fluid do you suggest for a stock disk/drum application?

Well, if you're truely replacing everything, then I might suggest using silicone-based fluid. It's supposed to be less susceptible to heat-induced problems, and doesn't attract moisture like standard fluids.

You do need to make sure everything is clean though, as silicone fluids don't mix with "normal" fluids. If you plan on re-using the distribution or proportioning valve, make sure to clean it thoroughly with alcohol. Same goes for any fittings that might not be replaceable. (T-fitting mounted on rear end, etc.)

I am not aware of any downsides to it, but there's more knowlegable folks on here that can point them out. I do suggest you consider availability of silicone fluids, as you may be on a road trip, and can't get it in some small town out in nowheresville.

Roger

I suggest not using silicone-based fluid. Its lack of hygroscopic nature (i.e., its not absorbing water) sounds like a good thing, but in fact it's not. Moisture will get into the brake hydraulic system with normal usage and changes in ambient temperature and humidity. Ordinary brake fluid is designed to absorb and assimilate a fair amount of moisture without causing substantial corrosion problems. With silicone fluid, the water will accumulate in slugs at the lowest points of the system...and stay there, where it will aggressively corrode whatever it's touching. This is not an improvement!

Furthermore, it is very difficult to get all the air out of silicone brake fluid, so it is very difficult to get a good, firm pedal.

There is an enormous range of conventional non-silicone brake fluids on the market. You can get whatever properties you want (e.g., high boiling point) without having to go to a silicone-based fluid.

And as if that weren't enough, the cost and effort difference between regular and silicone fluid is such that you can flush the system with conventional fluid every two years or so (which is about the right interval) for a long time before you equal the cost of just one silicone fluid changeover.

Shop carefully. All silicone fluid is "DOT 5". The highest spec category for non-silicone fluids is "DOT 5.1".

DOT 3 (original fill), DOT 4, and DOT 5.1 fluids are all intermixable.

DOT 5 (silicone fluid) cannot be mixed with DOT 3, 4, or 5.1.

Really, it should not be necessary to spend money on exotic brake fluids. Use a good brand of DOT 3 or DOT 4 (I have tended to use Castrol LMA DOT 4 when I can find it) and flush the system every two years and you'll be in fine shape.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

**********************************************************

Hmmmm.....I hadn't thought of it along those lines. If that were to happen, and your car had to spend even a short time in a freezing environment, then I suspect one could guarantee a split line or locked brakes.

Good call, Dan.

Roger

Well, practically speaking, if there's more than a really small slug's worth of water in your system, it's faulty and/or neglected.

We can get much higher performance brake fluid now than was available when our cars were new. I haven't looked around for brake fluid performance comparison tests — I imagine somebody's done them — but a couple weeks ago when I was shopping for half a litre of brake juice, I was faced with at least four choices of Prestone DOT 3 fluid. I don't recall all the varietal names, but there was one that said "for Ford vehicles", one that said "for ABS brake systems", one that was just plain, and...at least one other. All DOT 3, 4, and 5.1 fluids are intermixable, so there's no danger of a situation like "ohmygawd, I put Ford fluid in my Dodge/I put non-Ford fluid in my Ford".

Each of these multiple types of Prestone DOT 3 fluid had different boiling points (though there were two boiling points listed on each bottle; one denoting the minimum required for the DOT 3 category, and the other indicating the characteristic of that particular fluid…read carefully; the labelling isn't very clear. It's even more confusing than that; some fluids list both a dry and a wet boiling point, and some DOT 3 fluids have a higher (better) boiling point than some DOT 4 fluids.

Got a headache yet?

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Made a big decision and bought a jug of Dot 3, with a 284F wet boiling point and 470F dry boiling point...for ABS, Disc and Drum brakes.

I knew it was the right stuff for a slant, because it said it was for "today's modern, high powered vehicles".

I use DOT5 in both my cars and my cycle with no probs. If you got that much water in your system something is wrong. coming from a military background it doesn't concern me, we ran silicone in all the AirForce specialty vehicles ie. Hummers etc. with no issues. I haven't had any troubles with bleeding but is interesting to hear of that prob. would that be because of different viscosity? I like DOT5 because it doesn't eat the paint off everything it touches but the price may be cost prohibitive. Last I checked it was about $17.00/quart!!
Joe

_________________
70 Valiant 225,super six
65 Dart More Door race car 225/4bbl 8 3/4 3:91
70 Dodge D100 Sweptline short box 225/4spd

I use DOT 4 Valvoline or Castrol. Best insurance of all is to bleed them every year or two, and more if you are racing/autoxing.

Lou

_________________
Home of Slant6-powered fun machines since 1988

Yep, I don't think the brand matters much at all. Just buy a name brand in a metal can and flush it every year and you'll be fine. If you flush the fluid out every year you'll never have the brake system rot out. The ones that rot the wheel cylinders and all of that are the ones that run for 20 years with the same fluid.

That's gotten difficult; most of it comes in a plastic bottle nowtimes. Why should it matter…?

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Another vote for doing a flush every year. Thats what I do and never have a problem with the hydraulic's. I usually do it in the spring, after most of the wet weather is done.

DOT 4 generally has a higher boiling temperature than DOT3, but it also deteriorates (lowers its boiling temperature) faster than DOT3.

fwiw my '97 Audi A8 maintenance schedule mandates a brake fluid replacement at 2 year intervals, regardless of miles driven.

Brake fluid does deteriorate in the bottle. Get rid of any that has been sitting around for more than 2-3 years.

To flush a brake system first remove the fluid from the reservoir using a bulb syringe. I use a battery filling syringe dedicated to brake fluid use. Wipe out the residue and particulates from the reservoir using a clean lintless cloth. Fill with clean brake fluid. Flush the system. I installed Speed Bleeders on all my vehicles because I'm usually working by myself. They have a built-in check valve so you simply crack it open, pump the pedal ~10 times, then close it. Top off the reservoir and do the next wheel. Some newer cars require use of a factory scan tool to open the ABS actuator valves during bleeding. If you replace the fluid every 2 years, you won't need to worry about this.

Ken

No. This is important: the DOT 4 brake fluid category spec has a higher minimum boiling point, but some DOT 3 brake fluids have higher boiling points than some DOT 4 fluids.
Yup. It's because of fluid exposure to the air in the bottle once you open it. That's why I prefer the plastic bottles; once some of the fluid has been poured out, I can squeeze the bottle to raise the fluid level back up to the top (expel the air) then cap it tightly.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

I'm gonna split hairs on this one. True, the void in the bottle is filled with air as product is dispensed. The problem is that subjecting the air to repeated heat/cool cycles causes condensation to form on the inside of the sealed container. (Happens with air tanks on big rigs, too.) It's the water from condensation that corrupts the brake fluid, not the air. Dan's suggestion to squeeze the bottle, expel the air, then cap, takes care of the problem.

_________________
You can't fix stupid. - Ron White

I helped a friend bleed the brake system on a car that was used only as a showpiece from time to time, so he thought using silicone based brake fluid would preserve his system better. When test driving afterwards, we felt the pedal to be very spongy, so we re-bled the brakes. Twice. It turns out, a lot of others who tried silicone brake fluid experienced the same thing, a very spongy brake pedal with hardly any feedback. Dan tell it's because of difficulties getting the air out of the fluid, and that fits with the practical impressions. Stay away from that stuff, it is no good!
Olaf

_________________
Aspenized