Silicone brake fluid

[m37jarhead]

Unknown to me the previous owner of my M37 used silicone brake fluid.
While doing routine maintenance last week I bled the system using
standard glycol based DOT 3 brake fluid. I assume the whole system
now needs to be flushed. I've heard that we should use alcohol for this.
What proceedure do you recommend?
What, if any, are the problems with mixing the two fluids?
Any help appreciated.

[Lifer]

Oooops!

Yes, you will definately need to flush the entire system. Alcohol is a good choice of agents to do it with because it will absorb any water that may be present and any alcohol remaining in the system will evaproate quickly when air is forced through the system.

Once your system is thoroughly cleaned out, refill the system with one type or the other. (I'd use the "industry standard" DOT 3 because it is readily available everywhere, making it easy to top off the MC whenever necessary.)

Mixing alcohol-based and silicone-based fluids is not good at all. It will result in a gooey mess in very short order.

Once you flush your system, carefully inspect the inside of your rubber lines for damage/clogging. You may have to replace them.

[m37jarhead]

Thanks for the tips Lifer.
I'll start the removal of all brake fluid today and use alcohol as
the flushing agent.
Thanks again fur yur he'p.
m37jarhead

[MSeriesRebuild]

I've got my doubts that you can flush that mess out clean enough to eliminate issues from it.

[tmbrwolf]

I have this happen with fire departments all the time, we usually end up having to replace most if not all the wetted parts, flush it really good and hope there are no iffy rubber parts. Most of the time the rubber parts will swell up with the DOT-3 and start to leak, that is caused by a reaction between the DOT-5 and DOT-3 fluids, I would flush the system and go back to DOT-5,  I know it's not what you want to hear but better to get the word from someone with experiance dealing with the same issue. Hope for the best - expect the worst!

[k8icu]

I know I will probably get flamed for this...but....it has been my experience that the mixing of Dot3 and Dot5 will cause a jelloey mess is just an old SGTs tale.... David Doyle did an article a few years back in MV mag that showed that the two fluids could be mixed with no side effects. I was just rereading it the other day.... With that being said.....you should clean it out. Drain the system completely and then run rubbing alcohol through it replace with the fluid of choice and then fogedabouded. (for get about it).

[MSeriesRebuild]

Wonder why warnings on the containers of both types specifically warn against mixing? As always, somebody knows more than the chemist that blend the stuff. Anyway, I'm out of the flaming business, mix & match anyway you want is great with me. I will say I would never do it in my vehicle & no clients truck will leave out of our shop that has had a mixing of the 2 types without action being taken to absolutely correct the situation.

[uglyranger]

Here is the discussion David Doyle had on Steel Soldiers. Just click below:
http://www.steelsoldiers.com/showthread.php?p=283410

[tmbrwolf]

Well I'll add some more personal experiance here, NEVER EVER mix the two fluids, it WILL cause problems. Now some background on why I can say this. I was a Motor Sergeant in the Army when we made the switch to the silicon brake fluid (BFS) from the old DOT-3 (HB) brake fluids, my experiance was a dramatic increase in brake problems after the switch. If any component in the system was the least bit iffy it started to leak and we had brake failures! At one time just after the switch my motor pool had a 90% deadline rate for brake problems, and the division overall had a 70%+ deadline rate, we ended up rebuilding most of the brake systems in the motor pool because of leaks. After the repairs the brake problems disappeared and we had fewer problems than with the older HB fluid. The manufacturers say not to mix them... the military said not to mix them and my own experiance says don't mix them. So not to flame here but unless somebody can show me that my experiance is just flat wrong, I'll err in the side of caution and say DON'T MIX DOT-3 and SILICON FLUIDS bad things will happen!

[MSeriesRebuild]

Well I'll add some more personal experiance here, NEVER EVER mix the two fluids, it WILL cause problems. Now some background on why I can say this. I was a Motor Sergeant in the Army when we made the switch to the silicon brake fluid (BFS) from the old DOT-3 (HB) brake fluids, my experiance was a dramatic increase in brake problems after the switch. If any component in the system was the least bit iffy it started to leak and we had brake failures! At one time just after the switch my motor pool had a 90% deadline rate for brake problems, and the division overall had a 70%+ deadline rate, we ended up rebuilding most of the brake systems in the motor pool because of leaks. After the repairs the brake problems disappeared and we had fewer problems than with the older HB fluid. The manufacturers say not to mix them... the military said not to mix them and my own experiance says don't mix them. So not to flame here but unless somebody can show me that my experiance is just flat wrong, I'll err in the side of caution and say DON'T MIX DOT-3 and SILICON FLUIDS bad things will happen!

My experience is like wise. Some issues I'll experiment with, however brakes are simply not on my list of issues for experiments. Brakes are a life & death issue, for me that's plain enough.

[knattrass]

My brake experts at a small auto company in the D told me don't never mix. Pick one and stay with it. Given the high sit time to drive time we expect to get on our truck, Dot5 was the recommended. We replaced everything so it made the either/or decision easy. I am extremely glad we took the expert advice offered up here because we were one brake stroke away from a complete disaster. As luck will have it, the only skid marks were on the BVDs!

[k8icu]

Thanks for reading well guys.... I did say

.... With that being said.....you should clean it out. Drain the system completely and then run rubbing alcohol through it replace with the fluid of choice and then fogedabouded. (for get about it).

I wasn't advocating living with the problem....just going off of what Mr. Doyle had written in his article. Which was then presented in short format by uglyranger. If it was my truck I would probably bleed the system dry of all brake fluid, then run RA through it till it came out clear and then replace it with DOT5 for the reasons that knattrass stated about most of us not running our trucks on a daily baises.

[Lifer]

If I've done it right, here's a good explanation by a guy who's done his homework. It's a little long, but well worth the time to read it.

DOT 3 Vs. DOT 5 Brake Fluid
by Mike Nixon









This topic has always been a hot one, D.O.T. 3 brake fluid versus D.O.T. 4, versus D.O.T. 5. Which is best? Isn't D.O.T. 5 the hot set-up? Why are there different kinds to begin with, and what are the pros and cons of each? Let's explore all that, and hopefully in the process eliminate the hype and misinformation that often surrounds this subject.

Air? From Where?
Let's begin at the beginning. A brake system is not a sealed system. A physics principle known as Boyle's Law in a round-about way establishes that a fluid cannot leave a container unless air can follow it. If the vent in your gas tank plugs up, for example, fuel will eventually stop flowing. Similarly, a brake system is, like a fuel tank, vented to atmosphere, usually at its highest point, the reservoir. (Ever notice that little notch?) Thus a brake system has continuous access to air.

The Problem with Moisture
But that means it also has continuous access to moisture, for air naturally has moisture in it, to varying degrees. All brake systems have moisture in them, all the time, and this is unavoidable. There are two inherent difficulties with this that brake system designers must contend with. First, as moisture increases in the brake fluid, it tends to collect around the system's moving parts, particularly the pistons. If this moisture is allowed to increase, the pistons and surrounding areas will begin corroding and brake function will be seriously impaired. Corrosion is a big deal in brake systems, as anyone who has restored a vintage vehicle will attest. Nasty.

The other problem with this continuous exposure to moisture is that moisture makes the brake fluid more compressible. You don't want any compressibility in a brake system. For every millimeter that the lever or pedal moves, you expect a proportionate movement of the brake pads against the disc. If you don't have that, you have an unreliable and dangerous brake system. Unfortunately, brake fluid becomes more compressible as it increases in water content. Water contains hydrogen, and in response to heat cycles the brake fluid soon has air mixed into it as well as moisture.

Consumer-Friendly Brake Fluid
Brake system designers consider these issues thoroughly. To reduce the effect of both corrosion and compressibility, virtually all vehicle manufacturers use and specify a kind of brake fluid that is designed to not only accept significant amounts of moisture, but even to neutralize it by dispersing this moisture evenly throughout the system, thus preventing its concentration in any one area. It's actually kind of amazing what brake fluid does, when you think about it.

What Does the D.O.T. Rating Mean?
Eventually, however, because of this designed-in moisture management, the fluid gets overloaded and must be replaced. So important is this fluid replacement point that vehicle manufacturers have traditionally called for a maximum of a two year period of use of the fluid. By that time, the fluid will have started to turn golden, then light brown, indicating that it has absorbed progressively more moisture. Eventually, if left unchanged beyond the recommended service interval, the fluid will become dark brown, indicating high amounts of water absorption and thus badly contaminated fluid.

The importance of monitoring brake fluid's water content is further demonstrated by the fact that in the U.S., a brake fluid's most important classification is determined by the Department of Transportation, an arm of the National Highway Traffic Safety Administration. The D.O.T.'s rating communicates how contaminated with water the fluid can be and still work properly. In essence, how consumer-friendly it is. This is where the numbers 3, 4, and 5 actually come from. The D.O.T.'s rating focuses on the compressibility issue, and measures a brake fluid's ability to resist boiling into a very compressible gas even when new. This of course reflects upon its compressibility over time as well, after it has aborbed moisture and become incrementally more compressible. This is the fluid's so-called boiling point, which for most brake fluids centers around nearly 500 degrees Fahrenheit when new, and rapidly decreases with water content.

Incidentally, D.O.T. 3 brake fluid is for all practical purposes obsolete. D.O.T. 4, a rating that came about in response to the emergence of sintered metal brake pads during the early 1980s, has replaced it, being still a glycol fluid but with a slightly higher boiling point. Glycol brake fluid containers now are labeled "D.O.T. 3/4," presumably to eliminate confusion, as the two fluids are nearly the same. However, this seems to have merely raised more questions in most people's minds. The short of it is, if using purely organic (almost exclusively aftermarket, and usually, racing) brake pads, D.O.T. 3 will suffice. Otherwise, use D.O.T. 4.

Glycol Brake Fluids
Virtually all vehicle manufacturers specify one kind of brake fluid, whose base is alcohol. As we have already explored, this eminently ubiquitous alcohol (actually glycol) brake fluid is suited to the realities of vehicle ownership. It neutralizes moisture, turns color in direct proportion to moisture content, disperses moisture so that it doesn't concentrate, and resists heat related degradation that leads eventually to increased compressibility. Glycol brake fluid is clearly extremely forgiving, maintenance-wise. In fact, vehicle manufacturers use it because they are quite aware that the average owner will never change his brake fluid, let alone do so at the recommended maximum two-year intervals!

There are disadvantages to glycol brake fluid however. For one thing, the very attribute that enables it to accept moisture actually causes it to attract moisture, as any alcohol product will. For this reason, brake fluid suppliers recommend that only small amounts be kept on hand, and that a tight seal be kept on any unused fluid. (In the old days, it used to be available only in metal cans.) Another disadvantage, and a significant one, is that glycol fluid is chemically caustic, meaning that it damages other materials. It effortlessly removes paint and does strange things to plastic. (Even after it is wiped off, glycol fluid causes catalytic embrittlement, a chemical reaction on the molecular level that leads quickly to deep cracks. The ABS plastic used in motorcycle bodywork is especially susceptible.)

Silicone Brake Fluids
In years past, all brake fluids were glycol. Then D.O.T. 5, a silicone fluid having a higher temperature rating, emerged, initially to meet the higher boiling point requirements of racing use. (Race car brake systems include oil-cooler-like heat exchangers and ceramic pads.) Silicone fluid was able to withstand the most heat of any brake fluid, so it earned a reputation as a racing brake fluid. However, silicone brake fluid has properties very different from glycol fluid, and has its own pros and cons. On the advantage side, silicone fluid will not harm paint or plastic, and does not aggressively attract additional moisture as glycol fluid does. On the disadvantage side however, silicone fluid aerates easily. Harley-Davison, one of the sole current OEM users of silicone fluid, warns buyers to let the fluid sit at least an hour before using it. The trip home in the saddlebag is enough to aerate silicone brake fluid until it looks like a freshly poured soft drink. Silicone fluid is also slightly more compressible than glycol fluid, does not change color to tip the user to its moisture content, and worst of all, neither accepts or disperses moisture, making systems using it more corrosion prone, and requiring much more frequent fluid changes. Silicone brake fluid also lacks glycol fluid's naturally occuring lubricity, making it incompatible with the mechanical valving in some antilock braking systems.

A third brake fluid category could be included, if we were to consider bicycles. Their hydraulic brake systems use mineral oil, that is, baby oil. About the same consistency as glycol fluid, mineral oil is still not the best thing around paint, but in most other respects it is fairly non-corrosive. Like silicone fluid however, it does not deal well with moisture.

Which is Best?
As you may have noticed by now, instead of looking at brake fluid as D.O.T. 3/4 versus D.O.T. 5, we should see the issue as glycol versus silicone. This represents the larger division of type, and comparing D.O.T. ratings just isn't significant, especially since D.O.T. 5 fluids are now available in glycol formulation. Glycol fluids have improved until they now meet D.O.T. 5 standards. D.O.T. 5.1 for example, is a glycol fluid designed for certain ABS systems having mechanically cycling proportion valves. So now we have D.O.T. 3, 4, 5, and 5.1, with all but the 5 designation being glycol, while the 5 is silicone.

The real way to compare brake fluids is by deciding what is important to you. Is silicone fluid's safety around paint and plastic more important than yearly changes and a softer action? Its higher boiling point, the reason for its development and at one time its strong suit, is now academic, since D.O.T. 5 glycol (5.1) fluids are now widely available. Glycol fluid therefore is, for most of us, the better brake fluid, and the best just may be the 5.1, if the highest boiling point, which is really a moisture tolerance measurement, matters.

On the practical side, beware that glycol and silicone brake fluids are hugely incompatible with each other. Mixing even small amounts will create a sludge that looks amazingly like Italian salad dressing and is about as effective as a brake fluid -- meaning, not. Of further consideration is that, in some cases, the hardware designed for one fluid will not accept the other. Brake caliper and master cylinder seals, hoses, and other parts won't always work correctly when the type of fluid is changed.

Summary
Over the years, the debate has continued as to which is the best fluid. Racers and custom builders have traditionally promoted silicone fluid, and many street riders have assumed this meant it was good for them also. However, silicone is the highest-maintenence of all brake fluids, one that demands frequent attention. While this is acceptable in a race setting, it is less so in everyday commuting. The plain fact remains that vehicle manufacturers use glycol fluid because, with its being designed for the average consumer, it poses the least liability to them. In reality, the answer to the usage question is simple -- the brake fluid type the manufacturer recommends is the best. In most cases this will be the glycol fluid, the one that is designed to meet all of your brake system's demands and do so with very little fuss.


Mike Nixon

(Personally, I'm going to stick with the glycol stuff.)

[MSeriesRebuild]

This is a good article (assuming its factual correctness) giving detailed explanation. My disagreement with mixing of the 2 fluids is very clearly explained in the next to the last paragraph where complete incompatibility comes into play.

We have used both types of fluid many times, depending on owner spec & the end use of the vehicle, never had a single issue from the use of either product. We just don't mix the two in the same system.

Total honesty here, the price of DOT5 fluid discourages most folks from using it. At NAPA the cost of DOT5 fluid is $84 per gallon.

[ELBUFO]

Rule 1 never mix.
There that's it. I have used it forever. Only had one problem. My son decided to top off my clutch master cyl. He used some dot 3 he had. I noticed my clutch didn't feel right. Opened the master cyl and behold JELLO.
Mixing the two defiantly will produce the dreaded GOO. In lieu of a beating he tore the system apart. And now knows that all my (old) rigs run on silicone and synthetics period. Other than that ...works for me.