I am into redoing the brakes on my car. It is 4 wheel power drum 1970 GS. Since it will have new master cylinder, wheel cylinders, distrubution block on frame and all new lines on the front side of block. I am leaving the lines fronm the block to the rear as they are replaced in recent years. Could I or should I go to something besides DOT 3 like DOT 4 or DOT 5 ? I think the DOT 5is like sythetic or something will not lift paint etc..etc ? Car is street driven approx 1000- 2500 miles/year and 1 trip to the strip a year. Opinions and comments very welcome. Thanx Dave
Keep in mind that compatibility of different brake fluids is a different question (but, an important one) than you have since you appear to be involved in a complete rebuild and "virgin" fill of your rebuilt system. If you were adding brake fluid and NOT completely replacing all the fluid, you may have to deal with compatibility issues due blending different DOT brake fluid formulations, etc., as I have been told older system components may react to the DOT 5 formulations. I have been told so many times the best policy is always to flush and change the entire system rather than to start making a "cocktail" of different mixes in the brake system ... brake fluid rarely gets changed despite the recommendations to do so. Here is an article (below) on the subject (Link to the complete article): Fluid Dynamics Paying Attention to Brake Fluid Automotive braking is, as we all know, a really important factor in performance car building. The forward thinkers pay an equal amount of attention to stopping as they do to making their vehicles go fast. But, here's a fact that not too many realize: when you step on the brakes, you command a stopping force that's 10 times as powerful as the force that puts the car in motion [This Author has never driven a Buick GS - Ken]. Hard to believe isn't it? No wonder the performance brake market has been vying for and finally receiving our attention. But now that they've educated us in the importance of quality components, it's now time to pay attention to the fluid that activates and allows these awesome components to work. It only makes sense that after you've spent big bucks and a lot of time upgrading your vehicle, the completion of your job must go beyond adding just any old fluid into the system. It's extremely important to always use a high quality fluid. Let's face it, that quart of Elmo's Wonder Brake Fluid and Windshield Washer Solvent combo you picked up at the swap meet may end up as the only thing between the ball of your foot and a brick wall. So, let's at least pay a fraction of the attention spent on choosing components on choosing brake fluid. The following information should help you better understand the differences between various types of fluids. FLUID REQUIREMENTS Brake fluid must function through heat, cold, and all the variations of temperatures affecting all brake systems. In other words, brake fluid must be and must remain viscous (fluid) and resistant to severe conditions. It must also absorb water without having an affinity for doing so. Brake fluid must be pure and contain no contaminants, which will have a harmful effect on rubber components. It also should serve as a lubricant for the moving parts in a brake system and be able to withstand time and service--in other words, its boiling point and chemical properties must remain stable. One more important factor is that brake fluid should not cause an electrolytic action that will decompose or degrade metal brake parts. FLUID CLASSIFICATIONS These factors are taken into consideration by the Department of Transportation, National Highway Safety Administration in Federal Motor Vehicle Safety Standard 116. FMVSS116-classified fluids fall into three categories: DOT 3, DOT 4, and DOT 5. DOT 3 meets the minimum specifications, while DOT 4 and 5 meet more stringent requirements. The purpose of these requirements is "to reduce failures in the hydraulic brake systems of motor vehicles which may occur because of the manufacture or use of improper or contaminated brake fluid." In addition to setting the minimum wet and dry boiling points for all brake fluids, Federal Standard 116 deals with fluid viscosity, temperature and chemical stability, corrosiveness, water tolerance, compatibility (between formulations), and effects on brake system components. OK, WHAT'S THE DIFFERENCE? It seems logical that if DOT 3 is good enough then DOT 4 must be better. And, if DOT 4 is better, then DOT 5 must be better still. OK then, why? It all boils down to boiling point. When brake fluid begins to boil (from the heat that's generated in the system during braking) it forms gas bubbles. As these bubbles collect and grow, they form pockets of gas in the system. And since gas is much easier to compress than fluid, these pockets cause the pedal to easily compress or go soft. This is what as known as a spongy pedal--a condition that causes the heart to race. BOILING POINTS The following chart shows the aforementioned FMVSS116 minimum boiling points. These boiling points are the biggest difference in the fluid classifications. You'll notice there are two points for each classification of fluid. The dry boiling point is for fresh fluid that has not yet absorbed moisture. The wet boiling point is for fluid that has been in use (or in an opened container) long enough for it to absorb moisture from the atmosphere. CONNECTING THE "DOT"(S) The different DOT spec fluids have chemical or formulation differences, as well as boiling point differences. There are (at this point) three commercial formulations for brake fluids; two are glycol-based and the third is silicone-based. DOT 3 brake fluids are a mixture of polyalkylene glycol ether and other glycols (all start life as ethylene glycol--antifreeze); DOT 4 fluids add borate esters to raise the boiling point. DOT 5 is silicone oil based with additives. SILICONE BASE BRAKE FLUID (SBBF) The U.S. DOT defines silicone brake fluid as that which consists of no less than 70 percent of adiorgano polysiloxane by weight. Silicone-based fluids are regarded as DOT 5 fluids. They are highly compressible and can give the driver the feeling of a spongy pedal. The higher the brake system temperature, the more the compressibility of the fluid--increasing the feeling of a spongy pedal. Silicone-based fluids are non-hydroscopic, meaning that they will not absorb or mix with water. When water is present in the brake system, it will create a water/fluid/water/fluid situation. Because water boils at approximately 212 degrees F, the ability of the brake system to operate correctly decreases, and the steam created from boiling water adds air to the system. It is important to remember that water may be present in any brake system. Therefore, silicone brake fluid lacks the ability to deal with moisture and will dramatically decrease a brake systems performance. Silicone brake fluid has a number of strengths and drawbacks. Strengths: 1) It has a high boiling point since it does not absorb water. Therefore, there's no so-called wet boiling point. 2) Doesn't absorb moisture. 3) Doesn't remove paint. 4) The viscosity is more stable over the extremes of temperature. 5) With the exception of some formulations used in external boots, silicone brake fluid is compatible with all standard brake components. Drawbacks:1) It's hard to pour without entraining air bubbles--hence an application will generally have a softer, spongier pedal feel. 2) It doesn't absorb water, so any water already in the system accu-mulates in the lowest point of the system and stays there, causing rust. 3) Glycol fluids begin to compress near their boiling points, whereas silicone fluids begin to compress at around 300-350 degrees Fahrenheit. 4) Additives in the fluid can vaporize at comparatively moderate temperature, increasing the spongy feel. 5) Silicone fluids expand significantly when hot. 6) Silicone fluid is functionally incompatible with systems that have held glycol-based fluids for any length of time, requiring flushing and seal replacement (there are counter opinions on this, which state that the modern silicone formulations are in fact compatible with only a flushing, rather than a complete reseal). The actual DOT specification requires chemical compatibility, so as far as that goes, the two fluids won't cause reactions if used in the same system, but they certainly won't mix, either. 7) It's pretty much incompatible with anti-lock brakes because the silicone fluids tend to be more viscous, which can cause problems with the timing of the pulses that are intended to work with the thinner glycol-base fluid. This sometimes leads to damage of the ABS valving. The rapid pulsing necessary to anti-lock functions tend to cavitate the fluid, as the tiny bubbles collapse and coalesce into larger ones, and then collapse and reform into smaller ones. This tends to counteract the ABS effect and can diminish the actual effective braking. This condition also heats the fluid and can lead to even more sponginess and possible damage to the ABS controller. Thirdly, silicone brake fluid tends to foam when expressed from a small orifice under pressure, reducing its hydraulic effectiveness greatly. Minimum Dry Boiling Point Minimum Wet Boiling Point (All degrees in Fahrenheit) DOT 3 401 28 DOT 4 446 311 DOT 5 500 356
http://buickthunderforum.com/kb.php?mode=article&k=34 Brake Fluid Facts by Steve Wall As a former materials engineering supervisor at a major automotive brake system supplier, I feel both qualified and obligated to inject some material science facts into the murky debate about DOT 5 verses DOT 3-4 brake fluids. The important technical issues governing the use of a particular specification brake fluid are as follows: Fluid compatibility with the brake system rubber, plastic and metal components. Water absorption and corrosion. Fluid boiling point and other physical characteristics. Brake system contamination and sludging. Additionally, some technical comments will be made about the new brake fluid formulations appearing on the scene. First of all, it's important to understand the chemical nature of brake fluid. DOT 3 brake fluids are mixtures of glycols and glycol ethers. DOT 4 contains borate esters in addition to what is contained in DOT 3. These brake fluids are somewhat similar to automotive anti-freeze (ethylene glycol) and are not, as Dr. Curve implies, a petroleum fluid. DOT 5 is silicone chemistry. Fluid Compatibility Brake system materials must be compatible with the system fluid. Compatibility is determined by chemistry, and no amount of advertising, wishful thinking or rationalizing can change the science of chemical compatibility. Both DOT 3-4 and DOT 5 fluids are compatible with most brake system materials except in the case some silicone rubber external components such as caliper piston boots, which are attacked by silicon fluids and greases. Water absorption and corrosion The big bugaboo with DOT 3-4 fluids always cited by silicone fluid advocates is water absorption. DOT 3-4 glycol based fluids, just like ethylene glycol antifreezes, are readily miscible with water. Long term brake system water content tends to reach a maximum of about 3%, which is readily handled by the corrosion inhibitors in the brake fluid formulation. Since the inhibitors are gradually depleted as they do their job, glycol brake fluid, just like anti-freeze, needs to be changed periodically. Follow BMW's recommendations. DOT 5 fluids, not being water miscible, must rely on the silicone (with some corrosion inhibitors) as a barrier film to control corrosion. Water is not absorbed by silicone as in the case of DOT 3-4 fluids, and will remain as a separate globule sinking to the lowest point in the brake system, since it is more dense. Fluid boiling point DOT 4 glycol based fluid has a higher boiling point (446F) than DOT 3 (401F), and both fluids will exhibit a reduced boiling point as water content increases. DOT 5 in its pure state offers a higher boiling point (500F) however if water got into the system, and a big globule found its way into a caliper, the water would start to boil at 212F causing a vapor lock condition [possible brake failure -ed.]. By contrast, DOT 3 fluid with 3% water content would still exhibit a boiling point of 300F. Silicone fluids also exhibit a 3 times greater propensity to dissolve air and other gasses which can lead to a "spongy pedal" and reduced braking at high altitudes. DOT 3 and DOT 4 fluids are mutually compatible, the major disadvantage of such a mix being a lowered boiling point. In an emergency, it'll do. Silicone fluid will not mix, but will float on top. From a lubricity standpoint, neither fluids are outstanding, though silicones will exhibit a more stable viscosity index in extreme temperatures, which is why the US Army likes silicone fluids. Since few of us ride at temperatures very much below freezing, let alone at 40 below zero, silicone's low temperature advantage won't be apparent. Neither fluids will reduce stopping distances. With the advent of ABS systems, the limitations of existing brake fluids have been recognized and the brake fluid manufacturers have been working on formulations with enhanced properties. However, the chosen direction has not been silicone. The only major user of silicone is the US Army. It has recently asked the SAE about a procedure for converting from silicon back to DOT 3-4. If they ever decide to switch, silicone brake fluid will go the way of leaded gas. Brake system contamination The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some BMW owners changed to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. BMW brake systems should be flushed only with DOT 3 or 4. If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers. New developments Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation - which exhibit a minimum dry boiling point of 500F (same as silicone, but different chemistry). Additionally, a new fluid type based on silicon ester chemistry (not the same as silicon) has been developed that exhibits a minimum dry boiling point of 590F. It is miscible with DOT 3-4 fluids but has yet to see commercial usage. ----------------- Brake Fluids: DOT 4, DOT 5.1, and DOT 5 Silicone Q: Sir Tech, My bike's brakes are currently filled with DOT 4. Is it true that I will get better performance if I switch to Bel-Ray Silicone DOT 5 Brake Fluid? A: No, Years ago, many road race teams used DOT 5 silicone brake fluid to get higher boiling points than the DOT 3 & 4 brake fluids of that era. DOT 5 silicone is not hygroscopic, meaning it won't absorb water from the air, so it retains its high boiling point over time. On the other hand DOT 3, 4 and 5.1 brake fluids are glycol based and do absorb water from the air, which then lowers the boiling point. That is why you will see wet and dry boiling points, with the dry boiling points always being higher. Glycol based brake fluids may start out with a fairly high dry boiling point but as they absorb moisture the boiling point decreases. So every time your brakes get really hot and then cool, condensation occurs and moisture is absorbed. That is why it is important to replace your brake fluid regularly. It may seem obvious that DOT 5 silicone is the best choice, but not so. Today most road race teams use DOT 4 or DOT 5.1 glycol based brake fluids because the dry and wet boiling points today are very high and in some cases higher than DOT 5 silicone. The number one reason not to use DOT 5 silicone is a slightly mushy lever or pedal feeling as compared to glycol based brake fluids. This is the nature of the product. Street riders may not feel the difference, but the race teams prefer the precise feeling of glycol. The only motorcycles that I know of rolling off the production line with DOT 5 silicone are harley-Davidson and other American made motorcycles; and that is mainly where we sell our Bel-Ray Silicone DOT 5 Brake Fluid. I recommend you stay with the DOT 4 fluid for performance, not to mention the enormous job it is to switch your system over from glycol to silicone. If that job is not done properly, you run the risk of coagulation if remnants of DOT 4 are mixed with DOT 5 silicone. I hope that's not too much for you at once. Maybe you should read half, take a play break, then read the rest. DOT 5 Silicone versus DOT 5.1 Q: Sir Tech, The master cylinder cover of my bike says fill with DOT 5 brake fluid. Can I use your Bel-Ray Silicone DOT 5 Brake Fluid? A: I'll bet your bike is of European descent! In that case do not use DOT 5 silicone in your brakes. Use DOT 5.1 brake fluid. There is much confusion around this dilemma and making an error could be serious. DOT 5 silicone brake fluid is generally not recognized in Europe, so they call DOT 5.1 DOT 5 for short. In America, the brake fluids' names are DOT 3, DOT 4, DOT 5 and DOT 5.1. All are glycol and compatible with each other except for DOT 5 , which is, obviously, silicone based. In Europe beware, they do not recognize DOT 5 silicone and, therefore, call DOT 5.1, which is a glycol product, DOT 5. This can cause great confusion and obvious problems. DOT 5.1 got its start during the introduction of anti-lock or ABS brakes, where a light viscosity brake fluid was used to assist the modulation of the anti-lock mechanism. Suddenly DOT 5.1 is in vogue today and many are buying it under the guise that it must be better than DOT 4 because it is the next sequential number. Not so! To get the best performance brake fluid, check the wet and dry boiling points. In many cases, depending on the manufacturer, DOT 4 has higher boiling points than DOT 5.1. Today, DOT 5 silicone brake fluids are mainly used in the harley-Davidson motorcycles since this is what they come with from the factory. The advantage is that if any fluid spills, it won't damage the custom paint jobs. Do your community a favor and pass this info on to another European bike owner or, better yet, quiz your dealer to see if he is "in-the-know". DOT 4 VS. DOT 5 Silicone Coagulation Q: Sir Tech, I bought a 1987 harley-Davidson Sportster and I recently removed the front brake master cylinder cover to find a bunch of thick gunk inside. What happened and what should I do? A: If you own a harley-Davidson, think purple! Your H-D motorcycle came stock from the factory with DOT 5 silicone brake fluid and part of the regulated requirements for DOT 5 silicone is that it be purple colored so as to stand apart from the ever so popular DOT 3, 4 or 5.1 brake fluids which are glycol not silicone. Apparently, your hog's previous owner was more concerned with his tattoos turning green than with his brake fluid being purple and most likely added some DOT 3 or DOT 4 brake fluid to the system. This is a big no-no, bad boy! What happens when you introduce DOT 3, DOT 4 or DOT 5.1, all glycol based fluids, to DOT 5 silicone, which is obviously silicone based, is coagulation! The fluid will clot and, as you so eloquently described, form thick gunk. My advice to you is to consult a qualified technician. After all these are your brakes we are talking about! Have him fully flush the brake system and replace all the rubber parts with new ones and then go back to DOT 5 silicone brake fluid. If you do not re-build the master cylinders and calipers or replace all the rubber parts, there will most likely be remnants of the glycol in the rubber which will cause the problem again. To avoid "thick gunk" in your shorts due to grabbing the brakes and not impeding forward velocity, I recommend you heed my advice with the utmost seriousness and expedience.
I use DOT 5 in my '67 4 wheel drum brakes seems to work just fine now for three + years. I did do a complete brake overhaul with all new components. If this is what (information wise) you are looking for? It doesn't seem any "spongier" or different than it did before the change. Mike
I think will go with the DOT 4 and will flush system after a few years. I just not feeling warm and fuzzy with the DOT 5 yet. I think will install some speed bleeders and buy the DOT 4 and run cat with that. Dave
I replaced the entire brake system on my 65 when doing the frame off. I bought dot 5 and was ready to put it in. When checking and rechecking all the lines, I was told by a few guys that had tried dot 5, that it leaked easier than dot 4. Probably BS, but I was afraid of leaks as I was using all stainless lines which are harder to seat anyways. Well, I started to overthink and just went with dot 4 at the last minute. I only have a few miles on the car, but no brake issues at all. Not even a leak even with the stainless. My concern with the dot 3 and dot 4 was the paint. I was just very careful when topping off and when we bled the system.
