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Silicone brake fluid


buick5563
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Might depend upon the internal condition of the lines. Probably, if you can get clear fluid bled from them, then there might not be anything in them. Purely a judgment call. Why not use synthetic DOT4?

What about the condition of the rubber hoses? How old are they?

Curiously . . .

NTX5467

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Perfect time to convert to DOT 5 when you are replacing hoses and cylinders. its much less attractive to convert if you aren't replacing components for another reason.

The steel lines can easily be flushed with brake parts cleaner then blown out with compressed air. This is a very simple process. My personal preference is DOT 5. You never have to worry about flushing it and every time you flush the paint stripping concern of gylcol based fluid on a restored car is real.

Someone correct me if I'm wrong but it is my understanding that DOT 3 &4 fluids have been synthetic for a very long time. Suppliers are attaching the term synthetic to the label to give consumers more confidence.

The DOT 3 & 4 "synthetic is still glycol based and will still absorb moisture.

Certainly the synthetic blends have improved additives that may reduce this tendency in some brands, but as long as its gylcol based it will absorb moisture.

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JVRIV Never is a long time. While dot 5 does not absorb moisture/water, it can still get into the system via condensation. Since this moisture is not absorbed by the DOT 5, it will settle in low spots. If you live and store your car in an area that freezes, the straight water will freeze faster than that absorbed in DOT 3 & 4.

Depending on the area you live and how your vehicle is stored, you still need to flush the system containing DOT 5 at some intervals

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Silicone fluid raises havoc with the hydraulic stop light switches. If you run synthetic, carry an extrs switch as you will need it eventually,and they are not always available .

I agree I converted over to silicone and had to also change the switch. I ended up using a Harley Davidson stop switch due to a recommendation in the Torque Tube. I did have to change the electrical connections too, due to the switch.

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JVRIV Never is a long time. While dot 5 does not absorb moisture/water, it can still get into the system via condensation. Since this moisture is not absorbed by the DOT 5, it will settle in low spots. If you live and store your car in an area that freezes, the straight water will freeze faster than that absorbed in DOT 3 & 4.

Depending on the area you live and how your vehicle is stored, you still need to flush the system containing DOT 5 at some intervals

Barney,

You are correct "never" is a long time. Poor word choice.

As far as condensation forming inside a brake system from temperature changes, there needs to be a surface open to air in order for droplets of condensation to form. The only place that exists in a properly bled brake system is at the very top of the master cylinder between the fluid and cap. This is the same principal as the well known fact that keeping the gas tank full (minimizing surface area exposed to air) during winter prevents condensation in the tank.

You are correct that some moisture will eventually form even with DOT 5 however, it will be far less than glycol based fluids for a given amount of time. My experience has been that the majority of antique and classic car owners do NOT flush their gylcol based brake fluid until a failure occurs. It is not a pleasant task and the risk of a spashed drop going unoticed and removing paint isn't attractive. I have been guilty of the same thing depsite all the recommendations to bleed gylocol fulid every couple years and thats one reason I started using DOT5 15 years ago.

I have read on numerous occasions that DOT 5 is specified the US military in many vehicles. These are vehicles that must perform in wicked temperature extremes and environments. Obviously I don't know the maintenance schedule for flushing on those vehicles but when in combat/war that opportunity doesn't exist.

This is one of those topics that can debated forever and I think it comes down to personal preference based on ones own interpretation of what they read and experience.

Edited by JZRIV (see edit history)
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With all due respect, I think I'd rather have stainless steel brake lines and reasonably normal high-heat brake fluid.

Not EVERYBODY uses the messy two-person method of bleeding brakes--some use the vacuum hand pump's vacuum side attached to a piece of line which is placed on the bleeder screw so that NO fluid "splashes around.

An even better method is similar to the one used on the vehicle assembly line where the whole system has a vacuum pulled on it, then the fluid is added (at the master cylinder). A "field use" vacuum bleeder has a fitting block which attaches to the master cylinder (with the top off of it), where the cylinder starts with a certain amount of fluid in it, then a vacuum is pulled on the system and any "air" bubbles to the top of the cylinder. The SAME can be done on power steering systems! Special tools do exist, or can be easily built.

So, vacuuming from the top side, followed by careful vacuuming from each bleeder screw (to additionally bleed the system) could well be better than the "time honored" Press the brake pedal, steady, hold . . . open the bleeder screw, then closing it as the fluid flow stops . . . release the pedal . . . repeat if necessary, then at each wheel. The top-vacuum system was demonstrated on Two Guys Garage on Powerblock TV last weekend.

Although it doesn't apply to "antique" vehicles, if the system is on a GM vehicle and has a control module, the GM scan tool can "bleed" the system without removing any fluid from the system. It does this by very quickly cycling the solenoids, pulsing the system to force any "air" to exit via the master cylinder. Absent of such a situation on a few of my cars I've replaced the master cylinders on, I've quickly jabbed the brake pedal to produce + and - pressures in the system. Air will seek out the "high ground" during the "-" pressure times--usually works for me!

So, get some stainless lines, polish them with 600 grit Scotchbrite to get the "shine" off of them, and fill them with high-quality normal brake fluid. Add a hand vacuum pump kit (it'll come with correct tubes) or get the "top vac" kit.

Enjoy!

NTX5467

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I am sure I will get slapped for saying this.

I have put DOT 5 in literally hundreds of cars for 20 years. It will not harm anything. If someone had a problem after putting it in their car, they would have has it anyhow.

'nuff said.

Edited by wildcat465
Forgot to capitalize, crappy grammer tonight (see edit history)
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I am sure I will get slapped for saying this.

I have put DOT 5 in literally hundreds of cars for 20 years. It will not harm anything. If someone had a problem after putting it in their car, they would have has it anyhow.

'nuff said.

Well jeez! Share your process.................Bob

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Well jeez! Share your process.................Bob

I worked for a Honda dealer for many years. At 30000 mile intervals, we would do a brake fluid change.

A quart bottle of DOT 5 was obtained, I would turn it upside down on the master cylinder reservoir after cleaning it out. I would then take two old empty gallon jugs of washer fluid with a length of vacuum line stuck into it to the back of the car. Open the rear bleeder screws, put the vacuum line over the open screws and pump the brake pedal 40 times. Close the rear screws and move to the front. Open the front bleeder screws put the vacuum line over them and pump the pedal 40 more times. Close front bleeders and remove the inverted bottle, making sure the level was correct in the master. Oh yeah, do not let the reservoir get empty, obviously, then you need to bleed the whole system.

This procedure would push all of the old fluid and accumulated gunk out into the old washer fluid bottle and keep a solid column of fluid in the system avoiding air bubbles. Quick, easy, and 20 stalls of guys doing this multiple times every day. I cannot recall any problems with doing this for all the years I worked there.

I still change the fluid in my cars the same way now. You may need more than a quart for a larger car. The clear washer fluid bottle is handy because you can see the fluid go from dirty to clear once the new stuff has gotten all the way through. I cut a small hole in the handle portion and stick the vacuum line about 6 inches in. Seeing the crud that settles in the bottom is a bit of an eye opener.

I hope this helps.

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40 brake pumps? What kept the old fluid from being "recycled" back into the system as the brake pedal returned to its normal position? Isn't that why it took two people, one in the driver's seat pumping and releasing the brake pedal as the person under the car (with the car on a lift) saying "Press", then openning the bleeder screw as the pressurized fluid exited the wheel cylinder, "Hold", closing the bleeder screw, "Release" to let the brake pedal come back up and start the cycle again.

Certainly, how Paul said they did it would probably work as an "expedited" way of doing it

"solo". I don't recall the "duo" system taking 40 pumps, though. The "solo" system would probably cause enough + and - pressure pulses to help clean the lines, though, of "gunk". Interesting, though.

Enjoy!

NTX5467

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When Dow-Corning first brought out the silicone brake fluid, it was suspected to be one of the great things for vehicle brake systems where either ultra-high heat or high humidity issues were present. The great thing was that it was compatible with normal Dot 3 fluid, back then.

Seems like it would "mix" with normal fluid, too, so complete flushing (which was really not that prevalent back then, unlike now) was not really necessary, but recommended. With time, though, the two components of the "mixture" would separate out . . . at least in a jar.

The "big thing" was that in multi-piston-caliper disc brake systems (as in Corvettes, back then) could be refurbished with either new caliper housings or stainless steel sleeved caliper bodies and not expect to have any issues in the future. Of course, once the calipers had the stainless steel sleeves machined into the housings, that was usually the end of caliper issues with normal brake fluid. Funny thing, though, thinking about it in retrospect, single-piston calipers had NO issues with caliper piston bore degradation, but multi-piston calipers always seemed to. It would seem that such issues would be similar, but they weren't--presuming, of course, that the material the caliper housings were made of was the same.

DOT 4 synthetic brake fluid is used on the Holden GTOs, for clutch fluid on those vehicles, too. It's readily available under the Prestone brand at WalMart (of all places!), or at least the ones near us. You can read in the GTO forums about how the hydraulic clutch line runs close to high-heat-producing engine parts . . . and will discolor after a while. I think it's in the Corvettes, too, but I'd have to verify that.

Anytime there's a significant ambient temperature "swing" and the vehicle is not used enough to "cook" the fluid enough to remove any moisture, it's going to collect somewhere. If the fluid is more hygroscopic, the fluid absorbs it. If the fluid is less hygroscopic, no real place for it to go, I guess, once it might get inside the system (either from air space in the master cylinder--even in a closed system, there's always a little expansion room in the master cylinder). Now, back when brake system specs were upgraded a good while back, when perforance and composition standards for brake fluid was done ("Federal standards", of sorts), the issue of moisture intrusion was most probably considered. I can see where having a brake fluid which would absorb moisture would be advantageous. That way, any drops of moisture could become a part of the total fluid inventory, not unlike "Gets water out" gasoline additives (which used alcohol-based compounds to "absorb" the water and make it "burnable" in the engine) of those earlier times. In the "absorbs" orientation, this would also keep any accumulated moisture turning to "ice" in freezing weather and rendering part of the brake system ineffective (due to blocked lines, blocked with ice) until warmer ambient temperatures happened. Considering the options, I believe I'd opted for the more hygroscopic fluid, too. NOT to forget that most service stations had open gallon cans of brake fluid in their lube rack, year-round!

Back then, brake shoes were usually replaced in the 40K mile range. That also included flushing the brake lines, honing the wheel cylinder's "bore" surface, and putting everything back together. Worst case scenario was that new wheel cylinders might be needed. Disc brakes were not that prevalent during these times, except on sporty foreign vehicles, airplanes, and a "different" style of disc brakes on some middle 1950s Chrysler products.

Overhauling hydraulic brake systems was not a big deal, just a part of maintenance back then. I somewhat doubt that many people had enough continued brake use to really strain the boiling point of their brake fluid (one reason for the standards) . . . but even low-mileage vehicles didn't usually have wheel cylinder problems either. Yet when "collector cars" started to happen in the later 1970s, brake issues suddenly seemed to surface . . . from the vehicles sitting for extended periods of time with somewhat "moisturized" brake fluid. The Corvette 4-piston calipers were in a world of their own, it seemed. NOTE: In more recent times, it seems that we usually had to replace the rear wheel cylinders on the GM H-cars (i.e., LeSabre, Olds 88) in the 60K mile range, but by that time, the cars were at least 10 years old and were most probably NOT driven very hard by the particular age demographic of those owners, I suspect.

After Stainless Steel Brakes started doing the sleeved calipers for Corvettes, it seems like another evolution of their business was to custom-sleeve wheel cylinders for vintage vehicles?

As for the one post in the Olds forum regarding "mushy pedal above 10K feet altitude", that seems unusual to me. I can see the altitude having an influence on power brake booster assist vacuum, but not "mushy". Be that as it may.

In one respect, pondering the issue of IF the metallurgy of the drum brake wheel cylinders, and surface finish thereof (going along with the post about some "paste" applied to the insides of the new wheel cylinders) could be upgraded such that a smooother and harder finish might better resist the effects of "moisturized" brake fluid? Similar with the multi-piston caliper housings? But to me, the big question remains as to why the single-piston caliper systems usually had NO issues with brake fluid moisturization . . . from what I've seen over the years in North Texas.

Just some thoughts . . .

NTX5467

Edited by NTX5467 (see edit history)
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