mikesail Posted November 10, 2008 Share Posted November 10, 2008 After rebuilding the hydraulic system on my British Sports car for the umpteenth time, I asked myself why is there a need to use brake fluid for a clutch system. After all, this is just a fairly low pressure and temperature system, nothing special really. And we all know how brake fluid absorbs water and turns to crud over time, along with corroding the metal parts. So a few months back, I replaced the fluid with ATF, and have waited to see if the seals hold. The car is not being driven, but everything seems to be ok so far. So now I decided to take a further leap, and have replaced the fluid in the Bird with ATF. It has been in for about two weeks with no problem. The fluid does appear to have a bit more viscous drag which you can feel when rapidly pulling the clutch lever. Last night when it was quite cold ( at least for So-Cal ) the extra resistance was more notable. In driving the bike however, I do not notice any difference at all. I'm quite happy with the way it works and am finally used to seeing red fluid in the resevoir viewport. In retrospect, I think that jack fluid might be a choice with a little less viscosity, but I like the fact that ATF is a good lubricant, and is readily available. Also it is certainly able to take normal engine temps, I'm not sure about jack oil. I'm pretty confident that this will prolong the lifetime of the clutch system components, can't think of any real downside. Any comments??? Quote Link to comment Share on other sites More sharing options...
Iceman_40 Posted November 10, 2008 Share Posted November 10, 2008 I wouldn't have used ATF but I really can't see it hurting anything. I got sick of having my fluid turn dark, my brother races cars and pointed me towards the good brake fluid. Since I put it in 2 years ago it hasn't changed color at all. http://www.ate-na.com/generator/www/us/en/...bf_info_us.html Quote Link to comment Share on other sites More sharing options...
EVLXX Posted November 11, 2008 Share Posted November 11, 2008 Here's why... (copied from the above link) When the brake fluid starts boiling, it's too late. Braking gives rise to high brake fluid temperatures. In extreme cases the fluid begins to boil and causes vapor or gas bubbles to form in the brake system. This vapor or gas can be compressed allowing the brake pedal to be pressed all the way to the floor but the vehicles braking system is not functioning properly. So when your Bike fails to stop..... and your headed into traffic or off the road out of control... Just remember to say...... OH... SHIT ! Quote Link to comment Share on other sites More sharing options...
Zero Knievel Posted November 11, 2008 Share Posted November 11, 2008 He's talking using ATF instead of Brake Fluid in the CLUTCH. Still, I can't see what you're saving by doing that. Maybe a good idea if you need to fill a system and there's nothing else, but I'd stick with what's supposed to go in there. Quote Link to comment Share on other sites More sharing options...
Toynut Posted November 11, 2008 Share Posted November 11, 2008 Brake fluid is hygroscopic (water loving) and absorbs moisture in the system which typically permeates through the seals and various vent holes and gasket sealing surfaces. This acts to preserve the internal components of your hydraulic circuit. The boiling point of brake fluid is much higher than that of ATF (which starts to cook at about 260-300 degrees). The viscosity of brake fluid in colder temperatures is generally more stable and consistent than ATF as well. While you might get away with it in your clutch circuit (not sure for how long, though), I would strongly discourage it in your brake circuit. In addition, the clutch circuit is specified for a specific viscosity of fluid, cold temps may hamper the pressure release/disengagement of the clutch piston which may lead to increased clutch wear. BTW, some hydraulic seals are incompatible with ATF and will eventually swell and dissolve over time! Quote Link to comment Share on other sites More sharing options...
mikesail Posted November 11, 2008 Author Share Posted November 11, 2008 Brake fluid is hygroscopic (water loving) and absorbs moisture in the system which typically permeates through the seals and various vent holes and gasket sealing surfaces. This acts to preserve the internal components of your hydraulic circuit. The boiling point of brake fluid is much higher than that of ATF (which starts to cook at about 260-300 degrees). The viscosity of brake fluid in colder temperatures is generally more stable and consistent than ATF as well. While you might get away with it in your clutch circuit (not sure for how long, though), I would strongly discourage it in your brake circuit. In addition, the clutch circuit is specified for a specific viscosity of fluid, cold temps may hamper the pressure release/disengagement of the clutch piston which may lead to increased clutch wear. BTW, some hydraulic seals are incompatible with ATF and will eventually swell and dissolve over time! Thanks for the thoughtful response. This is strictly a question for the clutch circuit, I have no intention of messing with brakes. Any problems from the extra viscosity should be quite apparent to the operation of the clutch, I'm sure that will not be missed. The Hygroscopic nature of brake fluid is what I'm trying to combat. Are you confident in your statement that this helps preserve internal components??? I've seen many corroded brake systems, but not any internally corroded hydraulic jacks. But my experience is somewhat limited. And your last point is key. If ATF is not compatible with the seals, then I'll be rebuilding the system due to seal failure. My goal is to have a maintenance free system if possible. My belief is that brake fluid demands replacement and that other oils might eliminate this need. Quote Link to comment Share on other sites More sharing options...
Toynut Posted November 12, 2008 Share Posted November 12, 2008 Brake fluid is designed to be miscible in water and self-sacrifice some of it's properties (notably it's boiling point is lowered) as it is absorbs moisture. However, it still retains it lubricity as it absorbs water until it reaches it's saturation point. That's why it still needs to be flushed regularly. The new DOT 5.1 fluids (Wagner, Raybestos, Motul,etc.) give you an even greater margin of safety and performance. http://www.federal-mogul.com/en/Aftermarke...ingBrakeFluids/ Quote Link to comment Share on other sites More sharing options...
mikesail Posted November 12, 2008 Author Share Posted November 12, 2008 Brake fluid is designed to be miscible in water and self-sacrifice some of it's properties (notably it's boiling point is lowered) as it is absorbs moisture. However, it still retains it lubricity as it absorbs water until it reaches it's saturation point. That's why it still needs to be flushed regularly. The new DOT 5.1 fluids (Wagner, Raybestos, Motul,etc.) give you an even greater margin of safety and performance. http://www.federal-mogul.com/en/Aftermarke...ingBrakeFluids/ So you are saying that brake fluid is designed deliberately to absorb water, as opposed to my belief that such behavior is a side effect of creating a high boiling point fluid? I honestly do not know as my background didn't include any chemical engineering. Apparently silicone fluid has a serious deficiency in that droplets of water in the system can collect in the calipers and boil during a hard braking event causing total loss of braking. But to return to my desired application, clutch fluid, I still think this fluid replacement is plausible. One might suspect that automotive engineers choose brake fluid for clutch systems because it was already being used in the vehicle and worked well enough for this application. Quote Link to comment Share on other sites More sharing options...
Skull Posted November 12, 2008 Share Posted November 12, 2008 I'm not saying it won't work, but I will venture forth with the idea that it's not a conspiracy that the status quo is the status quo. Quote Link to comment Share on other sites More sharing options...
Toynut Posted November 12, 2008 Share Posted November 12, 2008 Apparently silicone fluid has a serious deficiency in that droplets of water in the system can collect in the calipers and boil during a hard braking event causing total loss of braking. Not only can they boil, but they can also freeze in their natural collection points, which include the master cylinder bores, junction blocks, metering valves, or low points in the brake circuit and such. The fact that Silicone fluid does not mix with moisture can create these problems, even though it maintains a very high boiling point (+500 degrees). In addition, silicone fluid is somewhat compressible and will lead to a "spongy" feel in the brake circuit (which is totally unacceptable in ABS applications). Racers used to use it in certain applications, but, it was typically changed very frequently during the race season. It is never used in snowmobile competition or other subfreezing applications (aircraft systems). Quote Link to comment Share on other sites More sharing options...
TuffguyF4i Posted November 17, 2008 Share Posted November 17, 2008 Brake fluid is designed to absorb water. That way you don't get pools of water in the system itself...it is in the fluid not pooling up. Condensation can be a big problem for brake systems. Quote Link to comment Share on other sites More sharing options...
blackhawkxx Posted November 17, 2008 Share Posted November 17, 2008 In my son's shop they buy power steering fluid and brake fluid in bulk, the bottles look the same. Someone put power steering fluid in the brake system in a older cadillac. The brakes worked for a day. Next day almost no brakes. They had to replace every brake part from the master through the wheel cylinders. Swelled the rubber parts. They lost some money on that mistake. Quote Link to comment Share on other sites More sharing options...
Warp11XX Posted November 17, 2008 Share Posted November 17, 2008 Condensation can be a big problem for brake systems. Bingo! We have a winnah.... Oil and water under most all conditions separate out leaving the water to collect in bulk somewhere and do nasty things to the interior of the system. If you notice next time you open a master cylinder after being a closed system for a prolonged interval, water will be the primary liquid trapped between the top gasket and the cover. That bit of H2O could theoretically migrate to the caliper as well. Cold weather is going to show the mechanical viscosity problem with oil as well. An old mechanics cheat is to add a teaspoon of brake fluid to the engine oil to swell the rubber and help stop seals from weeping oil. It sometimes works....for awhile... I didn't know that power steering fluid would do that as well to some seals. Quote Link to comment Share on other sites More sharing options...
rhubarbray Posted February 10, 2009 Share Posted February 10, 2009 One of the problems you`re going to find out about is the fact that brake fluid is glycol based and is perfectly compatible with a type of rubber called EPDM. ATF is a petroleum based fluid and uses a rubber called nitrile or Buna N. (I am disregarding synthetics for the monent). Brake fluid is NOT compatible with Buna N and ATF is not compatible with EPDM. You`re going to find the seals will swell and turn very soft. Quote Link to comment Share on other sites More sharing options...
mikesail Posted February 10, 2009 Author Share Posted February 10, 2009 One of the problems you`re going to find out about is the fact that brake fluid is glycol based and is perfectly compatible with a type of rubber called EPDM. ATF is a petroleum based fluid and uses a rubber called nitrile or Buna N. (I am disregarding synthetics for the monent). Brake fluid is NOT compatible with Buna N and ATF is not compatible with EPDM. You`re going to find the seals will swell and turn very soft. Thank you, now where were you before I started this hair-brained concept? Finally found a fluid compatibility chart a week after I did this, and saw exactly what you wrote, it was too late for the reservoir gasket by then. The master cylinder seals gave up a while later, so this turned out to be a significant bonehead move. I really would like to use a different fluid, but it appears that for the original seals that only alcohol or castor oil will be compatible. So back to brake fluid for now. Quote Link to comment Share on other sites More sharing options...
willxx23 Posted February 10, 2009 Share Posted February 10, 2009 The new DOT 5.1 fluids (Wagner, Raybestos, Motul,etc.) give you an even greater margin of safety and performance. http://www.federal-mogul.com/en/Aftermarke...ingBrakeFluids/ I'm with you, before I went to 5.1 I would have to flush/refill around every 6 months. I think I put my Galfer lines on about 7-8 months ago and just looked at the fluid today and it looks fine, I think I may make it an annual thing now. :icon_clap: Quote Link to comment Share on other sites More sharing options...
rhubarbray Posted February 13, 2009 Share Posted February 13, 2009 Another alternative you can do is switch to DOT 5. Won`t damage pain and won`t absorb water. It does however have microscopic air bubbles which may give it a slightly spongy feel at the lever. What we are required to do at work for fluids that do this is to put the fluid in a sealed container and draw a high vaccuum on the container for 24 hours. the bubbles expand, rise to the surface, and dissipate. BUT, DOT 5 is not compatible with DOT 3,4,or 5.1. A disassemble and clean is required but you don`t have to change the seals . A friend of mine runs DOT 5 in his V-Max and hasn`t had sticky pistons or any problems for about three years now and the fluid is still clear. Quote Link to comment Share on other sites More sharing options...
Toynut Posted February 13, 2009 Share Posted February 13, 2009 Another alternative you can do is switch to DOT 5. Won`t damage pain and won`t absorb water. It does however have microscopic air bubbles which may give it a slightly spongy feel at the lever. What we are required to do at work for fluids that do this is to put the fluid in a sealed container and draw a high vaccuum on the container for 24 hours. the bubbles expand, rise to the surface, and dissipate. BUT, DOT 5 is not compatible with DOT 3,4,or 5.1. A disassemble and clean is required but you don`t have to change the seals . A friend of mine runs DOT 5 in his V-Max and hasn`t had sticky pistons or any problems for about three years now and the fluid is still clear. DOT 5 brake fluid is silicone based brake fluid which may cause the problems listed in the above mentioned posts. :icon_nono: Quote Link to comment Share on other sites More sharing options...
TuffguyF4i Posted February 13, 2009 Share Posted February 13, 2009 The new DOT 5.1 fluids (Wagner, Raybestos, Motul,etc.) give you an even greater margin of safety and performance. http://www.federal-mogul.com/en/Aftermarke...ingBrakeFluids/ I'm with you, before I went to 5.1 I would have to flush/refill around every 6 months. I think I put my Galfer lines on about 7-8 months ago and just looked at the fluid today and it looks fine, I think I may make it an annual thing now. :icon_clap: Why did you have to refill and flush every 6 months? As mentioned before, DOT 5 does not absorb moisture. You NEED something that absorbs moisture to avoid corrosion. I believe the main benefit of 5 is the much higher boiling point, which is why it is used in applications where longevity is not important,,,,,ie racing. Quote Link to comment Share on other sites More sharing options...
willxx23 Posted February 13, 2009 Share Posted February 13, 2009 Why did you have to refill and flush every 6 months? As mentioned before, DOT 5 does not absorb moisture. You NEED something that absorbs moisture to avoid corrosion. I believe the main benefit of 5 is the much higher boiling point, which is why it is used in applications where longevity is not important,,,,,ie racing. I should have clarified that I meant the clutch side and not the brakes (as in the O.P.'s topic) , the clutch always got pretty dark colored (like coca cola) probably due to being exposed to the heat of the engine in the slave cylinder. The 5.1 though has held up rather well and is just as easy to work with and is compatible with dot 4.0. Seemed to be harder to find when I went looking for it but Cycle Gear here carries regularly. Quote Link to comment Share on other sites More sharing options...
rhubarbray Posted February 19, 2009 Share Posted February 19, 2009 Another alternative you can do is switch to DOT 5. Won`t damage pain and won`t absorb water. It does however have microscopic air bubbles which may give it a slightly spongy feel at the lever. What we are required to do at work for fluids that do this is to put the fluid in a sealed container and draw a high vaccuum on the container for 24 hours. the bubbles expand, rise to the surface, and dissipate. BUT, DOT 5 is not compatible with DOT 3,4,or 5.1. A disassemble and clean is required but you don`t have to change the seals . A friend of mine runs DOT 5 in his V-Max and hasn`t had sticky pistons or any problems for about three years now and the fluid is still clear. DOT 5 brake fluid is silicone based brake fluid which may cause the problems listed in the above mentioned posts. :icon_nono: Agreed, silicone won`t absorb water, but would regular maintenance and flushing alleviate those concerns? Assuming the reservoir cover seal is in good shape, how would the water droplets get in? Only way is by the seal or by the piston seals. I`ve got DOT 5 in my SRX 600 that I`m going to give a try to and see what it`s like. My friend with the V-Max that I was telling you about found that the slight sponginess he felt at the brake lever was a little strange at first but came to like it as it cave him a bit more modulation that a ridgid lever. Quote Link to comment Share on other sites More sharing options...
TuffguyF4i Posted February 19, 2009 Share Posted February 19, 2009 Moisture gets in with any condensation or any air. Brake systems aren't 100% sealed and air proof. You always have that bubble of air in your mast cylinder. Quote Link to comment Share on other sites More sharing options...
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