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MG MGB Technical - Brake Fluid
| What brake fluid should be used in a completely new brake and clutch system. Everything is new. Should I use the old DOT 4 synthetic, or a more up to date DOT 5 silicon. |
| Alex |
| go with the silicon. does not absorb water, and doesn't eat your paint if you should have a leak. There's got to be tons on this in the archives. I believe the other issues between dot 3 (i thought--don't know dot4) and silicon are boiling points, and compatability with master cyl. seals. I don't know about all that. I do know silicon works just fine and.....it doesn't eat your paint. paul |
| Paul Hanley |
| I'll go along with that Paul. I was waiting until someone else stuck their neck out. Some say that it provides little or no lubrication and others that it compresses and makes for a spongy pedal. Fluids compress about 5% by volume anyway both my cars have silicon fluid and the pedals are solid. |
| Iain MacKintosh |
| Alex, The other view Silicone fluids are NOT hydroscopic, meaning that they will not absorb moisture. This however is their downfall. All brake systems produce moisture. Particularly race brake systems as it is the extreme temperature changes that cause excessive moisture build up. As the brake system produces moisture, a conventional brake fluid will absorb it but a silicone fluid won’t. The moisture is still in the system but instead of absorbing into the brake fluid (admittedly reducing its boiling point), it just sits there in little water pockets waiting for the brake system to get hot so that it can vaporise. Even a well soaked brake fluid will have a higher boiling point than water. Paul |
| Paul |
| Another "other" view - DOT 5 silicone fluid has a spongey feel to the pedal - I would stick to DOT 4, it it just fine for road use. |
| Chris at Octarine Services |
| ATE Superblue is pretty good. |
| Glenn |
| Alex- Uh, oh! You've done it now! It's the old "Silicone Vs. Everything else" chestnut. Amongst the brake fluids presently available there are three possible candidates. The first, DOT 3, is a poor choice for high performance driving due to its low wet boiling point of F284 (dry boiling point F401) and is now generally considered to be obsolete. Be advised the American DOT 3 brake fluid is formulated differently than British DOT 3 and is incompatible with the Original Equipment natural rubber seals used throughout the brake system. It will slowly but surely dissolve them! The second candidate, DOT 4, is much better with a wet boiling point of (dry boiling point F446). Of the different Brands of DOT 4 brake fluid on the market today, Castrol LMA appears to be the best. The third choice is a synthetic fluid, Valvolene SynPower, which wins with a wet boiling point of F343 (dry boiling point of F513). DOT 5 Silicone-based brake fluid is a poor choice for any automobile as it has problems with air retention, making bleeding of the brake system a real bear, and poor lubrication, sometimes allowing the pistons of calipers and/or slave cylinders to bind in their bores and lock up the wheels. With a boiling point of F500, its performance is inferior to that of Valvolene SynPower. While it is true that silicone-based brake fluid does not absorb water, it is not commonly understood that water still gets into the system through the vent of the master cylinder and temperature drops resultantly cause condensation. Because water is heavier than silicone fluid, it will ultimately sink and gather in the lowest point in the system. Should it freeze, line blockage and brake failure becomes possible. It is also possible that should the temperature of the brake fluid rise above 212F, the water will vaporize, increasing pressure within the system and locking a brake. Should you decide to use silicone-based brake fluid, be sure that all of the seals are in excellent condition as it will easily find its way past a leaky seal and air will get into the system. Be sure to flush the system with denatured alcohol prior to refilling it with the silicone fluid. Failure to do so will result in the residual glycol-based fluid interacting with the silicone fluid to form a sludge which will destroy the seals in the system, resulting in catastrophic brake failure. Perhaps the only arguement in favor of silicone brake fluid is that it is slow to damage paint. However, if the brake system is leaking, it should be promptly repaired in the interests of safety. |
| Steve S. |
I agree with Glen on this one. Ate Super Blue is excellent high performance DOT 4 fluid. That's what we use in hotrod Mercedes and in Porsches. If you're looking for "regular" DOT 4 I'd go with Ate SL type or else Castrol LMA. The Ate (pronounced "ah-tay") in proper Kraut fluids are top quality. Rgds, Aaron Greenberg owner- MB Classic, LLC Service and Restoration for Vintage Mercedes-Benz Automobiles '67 BGT '76 TR6 |
| Aaron |
A question that has been bothering me for a while on this. How can you tell what type of fluid is in the system already? |
| Tim Boyle |
| Tim, Silicone fluid should be purple, DOT 3 or 4 is clear when fresh. For an interesting experiment about what happens when silicone and DOT 4 fluids are mixed lok at this; http://www.buckeyetriumphs.org/technical/Brakes/Fluid/Fluid.htm Clifton |
| Clifton Gordon |
| Natural rubber isn't used any more, at least in the USA, in the brake systems. I was talking to a mechanic friend (who also owns a TR4) and he laughed when I started talking about 'natural' rubber in braking systems. He told me they are banned, and have been banned for many years, because of their poor reaction to DOT mandated fluids. |
| Mike MaGee |
| Tim, DOT 5 is purple Probably the most expensive brake fluid Castrol SRF is rated a DOT 4+ and is a Silicon ester but is hydroscopic. As far as I am aware Ferrari F1 use a Brembro DOT 4+ Paul |
| Paul |
| Steve, something that was not directly stated, but I have wondered about, does Valvoline Synpower attack paint? I probably should go to whatever website Valvoline has and find out, but thought I would ask for the purpose of this discussion. Paul |
| Paul Briggs |
| Paul- Yes, it will harm paint if you leave it on long enough. However, it doesn't seem to be anything near as bad as DOT3 brake fluid. DOT4 seems less harmful to paint, but still needs to be cleaned off promptly. Valvolene SynPower seems kinder still. I once did spill a considerable quantity of it (about a cup) on my nice fresh engine compartment paint. (You can well imagine my screaming panic and the frenetic level of activity that followed!) and immediately washed it off with a solution of water and dishwashing detergent- no harm done. If anyone switches to silicone brake fluid because his master cylinder is leaking, then he's an idiot (I most humbly apologize in advance for upsetting all of the idiots out there who knowingly drive around with a leaking master cylinder). As I said before, if you know that you've got a master cylinder leak, you should fix it right away as a safety issue. Nothing like hitting the brake pedal while going down a winding mountain road and having it go to the floor! Doh! If you've got a master cylinder leak and don't know it, you simply aren't checking under the hood often enough. If the fluid is turning brown, the system should be flushed with denatured alcohol and refilled, then bled. |
| Steve S. |
| I sent an inquiry to Valvoline about SynPower and paint as I said I might, and here is their reply: Thanks for your note. The Synpower brake fluid will damage paint. Do not recommend getting this product on painted surfaces. The debate continues... Paul Briggs |
| Paul Briggs |
| Reading Steve S's comments has me reaching for DOT 4, however when I follow Clifton's link, I end up reading the Chicagoland MG article and reach for Silicon. http://www.chicagolandmgclub.com/techtips/525.html My MG will undoubtedly spend most of the year tucked up in bed, which makes comments regarding water and corrosion particularly apt. A local parts store offered DOT 4 Lockheed brake fluid, good as Castrol or not. |
| Alex |
| Alex, You got more than you bargained for here ! I mentioned the possible criticism being a spongey feeling pedal. Chris Betson picked this up but I must say that both my Bs which are properly bled have a solid pedal. My roadster in particular brakes just about as well as my Audi A4. |
| Iain MacKintosh |
| I have to agree with Iain once again. (Iain, did you think that was possible!) With silicon installed after complete renewal of the total braking system there were a few leaks that needed tweeks. And I spilled the fluid in the underbonnet charging the system for the first time. No harm done to a brand new paint job--including both axles--the rear of which was dripping wet as I neglected to fully tighten the three way connector. Currently, my car brakes hard and strong. No sponge whatsoever. I wouldn't ever drive the car with a known leak but the added insurance of being able to spot the leak after it develops and before harm is done sits well with me. I'm sure,like all fluids, the silicon should be changed on a regular basis thus eliminating the water. (I hope!) My MGA has developed a minute leak in the clutch master. No big safety hazzard. Paint near it--shot. Balance of the underbonnet paint--perfectly restored. Wish the A's PO had settled for the downsides of silicon. Just my observations. Paul |
| Paul Hanley |
| I thought someone might, thanks Paul. I for one can't stand the corosion which DOT 4 causes especially in a car that's not used a lot. I want to build a system that hopefully I can forget apart from fluid level checks etc. The only thing that still niggles me are the comments about a spongy pedal. There must be something in this but my two cars one of which has standard hydraulic flexibles and the other metal braided both have hard pedals. Silicon fluid is very easy to aerate so maybe this is a factor which contributes to the sponginess as fluids are considered to be virtually incompressible. |
| Iain MacKintosh |
| When my TR6 was restored, every component in the braking system was either replaced or repaired, with all new seals, and then filled with DOT-4. About 2 years later, the M/C developed a leak, spoiling the paint under it. I rebuilt the M/C and replaced the DOT-4 with DOT-5. I did it by simply pouring DOT-5 in the M/C and bleeding the brakes until I could see no traces of the old DOT-4. I did NOT flush the system with alcohol. Eight years later, the M/C again developed a leak. Two years with DOT-4 vs eight with DOT-5. Not a statistically valid sample, I know, but something to think about. It at least indicates that DOT-5 is no more of a problem than DOT-4, even if all the old DOT-4 isn’t flushed out before adding DOT-5. I had no trouble bleeding the brakes, and during that 8 years, my brake pedal had just as firm a feel as it had before. I drove cross country in a caravan with a friend in another TR6 with DOT-4 brake fluid, and we swapped cars from time to time; neither he nor I noticed any difference in the pedal feel between the two cars. My friend is in the rabid anti DOT-5 camp, so if he had felt a difference, he would have let me know. As for water getting into the system with DOT-5, I’m convinced that is pure nonsense. How is water going to get into the system? The only interface between the fluid and the atmosphere is at the top of the M/C reservoir. Since silicon does not absorb water, no water will be absorbed from the air. The only way for water to get into the silicone fluid would be for liquid water to be standing on top of the fluid in the reservoir, and then sinking to the bottom. How can this happen? Condensation? Water will only condense from the air when warm, humid air comes into contact with a cold surface. Under what condition will the silicon fluid be cold while sitting in a warm, humid environment? Maybe if you leave your car outside on a cold winter day after work while you eat supper and watch TV, and then move it into your warm, humid garage before the engine has time to warm up and heat the brake fluid. Even at that, water accumulation would be minor, as there is only a pinhole at the top of the M/C fill cap. In every other case I can think of, the brake fluid in the reservoir will be at or above ambient temperature, so no condensation will take place. I’m certainly no expert, but until I have definitive data to the contrary (and I don’t expect to), I will continue to use DOT-5. Y’all can do what you want. For a more definitive study, check on the Buckeye Triumph web site for a good (really good!) engineering analysis of brake fluids by Nelson Riedel. http://www.buckeyetriumphs.org/technical/Brakes/Fluid/Fluid.htm |
| Dan Masters |
| Is Dan Master's contribution a knock out blow in favor of DOT 5 silicone, or not. |
| Alex |
| I will avoid the controversy about silicone fluids absorbing water or not ~ just plain ignorant of the facts, but I will say these few things taken strictly from experience. 1) Valvoline SynPower synthetic brake fluid, as used in my cars and truck, is easily cleaned up without repercussions (as Steve S. says) IF you get it cleaned up quickly. The operative word here is quickly. 2) That same fluid has consistently given me good hard brakes and bled as easily as any other Glycol fluid. I did NOT have good luck with Silicone fluids initially as it applies to these qualitities and steered clear of them (read the archives, if it matters, about MY BAD LUCK with GE Silicone fluid from the late 80s) until I bought a 73 roadster from a friend which had recently (2001) been converted to a new millenia silicone fluid. My friend had used the silicone fluid Moss sells and frankly, it gave just as hard a pedal as any car or truck I have ever driven. I still use the Valvoline fluid, however, and flush every two years with excellent luck about seals and wear, but I must admit that somebody has improved silicone fluids since my bad luck, in my opinion. And perhaps that is the real point of any fluid or rubber seal you can use/choose for your brake system these days ~ that things change because of research, product improvement, and feedback to producers from actual field testing and fleet surveys and experiences. The arguments about Silicone vs. other fluids will likely continue, but I think we all need to realize that the basis for our arguments may be based on outdated and no longer accurate information. Funny thing, I think this applies to a lot of other matters as well. JMHO |
| Bob Muenchausen |
| Bob, may I pat you on the back? Enough said. Dan, one thing to consider when it comes to water in brake fluid is weather. Some of us live in rather harsh and/or wet environments where water and condensation will find their way into everything. If everyone kept their brake system in tip-top shape, it should be a non-issue, but unfortunately, that's not case. Besides, we should all understand the precautions of long-term use of silicon fluid. Its sort of like changing your oil every 3 years because you only drive 1000 miles a year... |
| Jeff Schlemmer |
| Jeff, No matter where you live, moisture will not condense unless the temperature of the silicone fluid is significantly less than the temperature of the surrounding moist air. If you park your car in an air conditioned garage and then drive it out into a hot, humid environment on a regular basis, then you might have a problem. Even then, I would expect the problem to be minimal, as we are only talking about a short period of time before the fluid warms up to a temperature equal to or higher than ambient, and then there is only a tiny hole for the water to condense in. Given that silicone fluid does not absorb moisture, the presence of high humidity alone is not a factor, moisture must condense and puddle on the surface of the silicone to cause a problem. Wallpaper, curtains, clothing, bread, etc, will absorb moisture out of the air, and will become damp just from the presence of humidity. In that case, mold is usually the end result. As for raw water, I would be very surprised if any one drives in conditions where raw water would be splashing up onto/into the brake M/C with any regularity. But, if you do encounter any of these conditions, then yes, it might be a good idea to change your fluid on a regular basis. |
| Dan Masters |
| Silicone fuid may have its place, buts its not cheap. So a museum car may be acceptable , but fast road use? http://www.apracing.com/car/brakefluid/ Silicone (Dot 5) is not for high performance despite high temp????????? If it was then the supply would not be restricted, well apart from it does not work with ABS??? and not recommended for racing??? These may be mind games but which racing team uses a Silicone fluid????? The reasons for using Silcone Dot 5 is it does not to damage paintwork!!! why could this be a problem 1) poor maintenance, IF SO!! 2) You like to spray your car with brake fluid. Dot 4 is cheaper and works for most applications, but means a regular check on braking system, good idea, and being careful not to spill braking fluid, good idea! Why do you wish too use DOT 5? Paul |
| Paul |
| I don't care how well you maintain your brake system, leaks can and do occur. When they do, if you are using DOT-4, you will lose paint wherever the leak occurs. My M/C seals failed after only 2 years and allowed DOT-4 to leak and eat the paint under the M/C. This M/C was a new unit purchased from one of the big 3 vendors, so it was not poor maintenance on my part. I don't care how careful you are, there is always the potential for spilling fluid when maintaining your brake system. If you've never spilled anything, my hat is off to you! DOT-5 is expensive, but not near as expensive as a repaint. I don't race my TR6, it doesn't have ABS. DOT-5 works perfectly for me, and I drive my TR6 about as spirited as any one. Living in East Tennesse, my brakes get a good workout! You can use whatever you prefer, but I'll stick to DOT-5. It works perfectly, has no drawbacks whatever in my application, and does not eat paint! DOT-5 costs more than DOT-4, but it's still dirt cheap compared to other things I have to buy to maintain my car. If you want to base your opinion on a product from information supplied by a company that sells a competing product - good luck! In that case, try http://www.russellperformance.com/kart/kart_dot5_silicn_brakfluid.htm |
| Dan Masters |
| I have had silicon fluid in our TD's braking system ever since I completed a restoration on the car almost 20 years ago. In that time, I have never changed the fluid or flushed the system. The master cylinder lives under the driver's side floor board where it is fully exposed to the elements. We live in the Pacific Northwest, known or it's rain and we drive the car on a regular basis regardless of weather (we have even driven it in the snow on more than one occasion). In that period of time, the fluid has remained as crystal clear as when it was originally installed in the system (the purple color has faded so that when one looks down into the master cylinder the impression is that there is no fluid in the cylinder as one is looking right to the bright shiny bottom of the cylinder - there is fluid in the cylinder, clear to the top, but it is so clear that it is invisiable). Based on the above, I have to agree with Dan Masters, that the issue of water in the system is an non issue. I find it interesting that the only claims of water getting in the system with silicon fluid as a result of condensation and sinking to the lowest point and causing corrosion is ALWAYS a claim made by companies that do not produce silicon fluid, such as AP Lockheed. Interestingly, with all these claims floating around and being brought up with every discussion of silicon fluid, I have never run into anyone who has experienced the problem. Based on thisI have to consider these claims to be more marketing hyporbla, based on half truths that are being used to try and scare people away from using someone elses products. Silicon fluid is not a cure all and not for every braking system. Systems with small orfices or rapid action of the braking system, such as automatic proportioning valves and anti lock braking systems should definitely NOT use silicon fluid since the small orficies and rapid operation of the system will cause airification as a result of cavitation of the fluid, which will certainly cause a spongy pedal. I experienced that problem when I tried using it in the clutch hydraulics of our MGB and have since changed back to DOT 4. However, in cars with simple braking systems that have orfices large enough to drive a truck through and cars that are not driven a great deal or spend the winter months in storage and cars with $10,000 paint jobs on them, my experience is that silicon is the way to go. Cheers - Dave |
| David DuBois |
| David, Don't see what's wrong with DOT 5 fluid in MGB clutch either unless of course you have changed the copper pipe From 1/4 to 3/16 in which case the fluid velocity will have increased and may be causing the problem. Both my Bs have DOT 5 in brake and clutch, no problems bleeding or in operation for several years. |
| Iain MacKintosh |
| The most important thing in my opinion is no matter what you use fluch it out with clean fluid once a year and you'll have much better service. This will also take care of your moisture problem. Bob/International Auto |
| Bob Thompson |
| In the case of silicone DOT 5, air is quite happy to take up residence between the brake fluid molecules (not visible), and as a result the fluid compressibility goes down and you have air in the system which cannot be bled out. A point of interest is that Castrol SRF a silicon ester is actually made to absorb water, despite being for race applications when the fluid is changed on a more regular basis than a road car, if water cannot enter system then what is the point of making it hygroscopic. Paul |
| Paul |
| I think that one of the most interesting sections of the article Clifton linked to is this: ======================== The likely primary way moisture gets into the system is through the brake hoses. Recall that there are short hoses near each wheel to allow for suspension system movement relative to the frame. Hugh Fader passed on copies of two reports to the Society of Automotive Engineers (SAE) after he learned that I was writing up something on brakes. One by G. R. Browning of General Electric Corporation presented in 1974 reported on comparison studies of glycol-based and silicone fluids. In a test of water permeation of brake hoses, one hose was filled with commercial glycol-based fluid and the other with silicone fluid, both ends were capped and the hoses submerged in water. The results are were: Brake Hose Moisture Absorption Test Moisture Content of Fluid Before Test - After 7 days Emersion - After 35 Days emersion glycol-based Fluid - 0.15% - 3.03% - 6.9% silicone Fluid - 0.01% - 0.03% - 0.03% Note that the silicone fluid absorbed an insignificant amount of water, it also prevented water from entering the system though the brake hoses. ========================= |
| Rob Edwards |
| "...you have air in the system which cannot be bled out." As I and others have pointed out in this thread, this is simply not true, at least for the applications we are speaking of here. |
| Dan Masters |
| Dan Silicone DOT 5 fluid is more compressible, how do explain this? or are you denying this is not true? Paul |
| Paul |
| Paul, I believe we've worn this thread out. I've stated what I believe, and I've stated what I know. There's nothing more I can add. The previous inputs to this thread, mine and others, have said it all. DOT-5 works for me. If it doesn't work for you, so be it. This ends my participation in this discussion. |
| Dan Masters |
| I have always noted an improvement in clutch operation with silcone fluid as well. Bob |
| Bob Thompson |
This thread was discussed between 29/03/2004 and 04/04/2004
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