Owen Posted February 26, 2001 Share Posted February 26, 2001 Hi all, I have the Tilton master cylinder unit for use with my T56. It says Dot 3 only, is there any problem with using Dot5 instead? I dont want some kinda seal being eaten up etc. Also, I'm assuming I should flush the thing completely. Any tips on that? Thanks. Owen ------------------ http://www.homestead.com/s30z/index.html Quote Link to comment Share on other sites More sharing options...
DavyZ Posted February 26, 2001 Share Posted February 26, 2001 Owen, from what I gather from the mechanics here at work, DOT 3 and 4 are ok, but NOT 5-the DOT 5 is thicker and not compatible. Man, if it says DOT 3, why not just use it? David Quote Link to comment Share on other sites More sharing options...
Dan Juday Posted February 27, 2001 Share Posted February 27, 2001 Well, I pumped 3 pints of DOT 3 through mine and I still don't have it bled. So I need help too. You guys with working clutchs help us out! Dan Quote Link to comment Share on other sites More sharing options...
Owen Posted February 27, 2001 Author Share Posted February 27, 2001 "Man, if it says DOT 3, why not just use it?" ***Mainly because DOT-5 is supposed to be better for brakes. So I figure why not for the clutch hydraulics too? Owen ------------------ http://www.homestead.com/s30z/index.html Quote Link to comment Share on other sites More sharing options...
blueovalz Posted February 27, 2001 Share Posted February 27, 2001 3 pints???!!!. If the garage floor is still dry, that's one of them there enigmas. Even my hydraulic throwout bearing didn't use that much. Terry Quote Link to comment Share on other sites More sharing options...
DavyZ Posted February 27, 2001 Share Posted February 27, 2001 Owen, I'm not trying to be abrasive--I'm just relaying the information my mechanics gave me. Give the DOT 5 a try and let us know what you find out; it may work really well! David Quote Link to comment Share on other sites More sharing options...
Owen Posted February 27, 2001 Author Share Posted February 27, 2001 Yeah sure, make me the guinea pig and have my tranny blow up all over the street! I did check a little on the internet and some companies were using DOT 5. I'll check some more. Owen ------------------ http://www.homestead.com/s30z/index.html Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted February 28, 2001 Share Posted February 28, 2001 DOT5 is the silicone stuff right? If so that's what I'd have probably used! The reason is that the silicone fluid boils higher, doesn't absorb water, and oh yeah doesn't EAT paint. It's that last that I really like, that and not absorbing water to eat up myinternal metal parts and turn brown. Hydraulic fluid is a noncompressable fluid - works like a cable would in your Ebrake only it can be routed all over the place and exert far more pressure. I'm puzzled as to why thickness would be an issue unless it was being forced through tiny little holes or seals somewhere? I guess I'm just not sure I understand why DOT5 would be "bad"... Quote Link to comment Share on other sites More sharing options...
Owen Posted February 28, 2001 Author Share Posted February 28, 2001 some info i found about air or water in the system 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 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. From a lubricity standpoint, neither fluids are outstanding, though silicones will exhibit a more stable viscosity index in extreme temperatures. Neither fluids will reduce stopping distances. Stolen from the Airheads BMW Club newsletter - July 1995 Battle of the DOTs DOT 3-4 Verses DOT 5. Which brake fluid should I use? From Oak Okleshen #35 "With regards to the DOT 3-4 verses DOT 5 brake fluid controversy, here is an article sent to me by Mr. Steve Wall. It is one of the most professional treatments I have seen on the subject". [i had to condense this article from 6 pages to 1 due to space limitations -ed] 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. for what its worth...note, dont believe it just cuz its on the internet! Owen ------------------ http://www.homestead.com/s30z/index.html Quote Link to comment Share on other sites More sharing options...
BLKMGK Posted March 1, 2001 Share Posted March 1, 2001 Doh! Sounds like DOT5 isn't quite the panacea I thought it was. Hrm, so it doesn't eat paint but has lot's of other bad properties? Guess I had better check what's in that BIG bottle out in the garage I've been using for so long (sigh). Quote Link to comment Share on other sites More sharing options...
Owen Posted March 1, 2001 Author Share Posted March 1, 2001 You only have to be careful not to add any air or water, just like any hydraulic system. So I would still use it, I'm just wondering what it would do to my Tilton which says DOT3 only. I'm a little worried about the build-up mentioned, though. My brake lines underneath the car are stock still. The new DOT5.1 is supposedly an improvement of DOT4, but I don't know if it's available. Owen ------------------ http://www.homestead.com/s30z/index.html Quote Link to comment Share on other sites More sharing options...
TimZ Posted March 1, 2001 Share Posted March 1, 2001 We are still talking about the clutch here, right? I was considering converting the clutch hydraulic system over to silicone, since I live in the north, and the car sits most of the winter. Silicone is supposed to be better for that. I was only going to change over the clutch, though. After reading that article, I'll think I'll skip the hassle of converting, and keep the glycol based stuff. Thanks. Really, for the clutch, the temperature requirements are much lower, and you don't need to use a high temp fluid. Some of the DOT4 fluids are more resistant to water, so that would be a good reason to use DOT4, but I wouldn't spend too much time worrying about finding an expensive high temp racing fluid for the clutch. Quote Link to comment Share on other sites More sharing options...
Mike kZ Posted March 1, 2001 Share Posted March 1, 2001 Good stuff!, I was just going to use Dot5 to do my entirely new brake system (lines and all)this weekend. After reading that article, I think I will be returning the Dot5 and go with Dot4! Thanks for the info! ------------------ http://members.tripod.com/~SnowSurfer/mikekz1.html Quote Link to comment Share on other sites More sharing options...
TimZ Posted March 1, 2001 Share Posted March 1, 2001 quote: Originally posted by Owen: You only have to be careful not to add any air or water, just like any hydraulic system. So I would still use it, I would not recommend using the DOT5 silicone fluid for the brakes. I have never heard a single good thing about DOT5 in a performance braking application. The attached article above alludes to it, but even though the silicone fluid has a higher boiling point, it doesn't behave very well as it starts to get near it. The reports that I had read mentioned that some of the chemicals used in the fluid start to outgas before the boiling point is reached - resulting in a spongy pedal (at best). I've heard this account too many times to ignore it. Here are a couple of other sites to check: http://www.muller.net/karting/docs/technical/brfluid.html http://www.rpmnet.com/techart/fluid.shtml http://www.panteracars.com/motul.html The last one is a source for the DOT5.1 fluid - I thought that they used to have an article about DOT5 buried there, as well. DOT5 (silicone) could be a reasonable solution for the clutch hydraulics, due to the lower temperature requirements, but I would never use it in my brake system. Quote Link to comment Share on other sites More sharing options...
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