I think you have answered your own question
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| DOT5 silicone brake fluid problems.. https://www.ausmini.com/forums/viewtopic.php?f=2&t=95955 |
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| Author: | Minimad [ Sun Aug 27, 2017 7:29 pm ] |
| Post subject: | DOT5 silicone brake fluid problems.. |
Hi, Anybody out there had problems with DOT 5 brake fluid?? We completely rebuilt / replaced the brake system on a cooper S a couple of years ago. Everything was fine up until a month ago, Now the brakes are sticking on and then overheating. As you drive it the pedal just gets harder and harder so pressure building up in the system. To get the brakes to release you can either let it cool down (a couple of hours) or crack the line open on top of the master cylinder. Any thoughts appreciated.... Should I go back to DOT 4.? |
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| Author: | Minimad [ Sun Aug 27, 2017 7:36 pm ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
This is what I am worried about.....(No i'm not running Brembos but I would expect that the rubber is 'natural') From the Brembo Technical Notes All brembo braking products use natural-rubber base seals, and therefore are INCOMPATIBLE with DOT-5 SILICONE-based brake fluids. DOT- 5 SILICONE-based fluids react with natural-rubber seals to swell them WHICH CAN CAUSE SEVERE PISTON RETRACTION PROBLEMS. There is no cure for problems caused by DOT- 5 use other than complete seals replacement - USE ONLY DOT-3/4 NON-SILICONE TYPE FLUIDS such as CASTROLTM 'LMA' in your brembo components. Also from Minispares for their new master cylinders... 'Ensure the correct DOT4 or DOT5.1 brake fluid is used as these cylinders are not designed to use anything else such as Castrol SRF for racing or any mineral fluid.' |
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| Author: | 9YaTaH [ Sun Aug 27, 2017 8:18 pm ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
I think you have answered your own question
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| Author: | Minimad [ Sun Aug 27, 2017 9:07 pm ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
9YaTaH wrote: I think you have answered your own question I'm holding out for a glimmer of hope that others maybe using it with no problems..... 
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| Author: | FNQ [ Mon Aug 28, 2017 8:43 am ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
sorry not really a definitive answer more of a guess but i concur go back to dot4 AND replace all seals, or possibly change to SRF ( costly) and use the genuine AP seals. Further more , once used in a silicon environment , is there any any issue with rubber brake line components( not just seals) reverting to DOT 4... being they are slightly water permeable??? no idea really but as we are talking about stopping power better to be safe than sorry. and finally , maybe two years of seal life is THE MAX, for the new breed of natural rubbers, so maybe silicon systems will swell and polyglycol sytems will weep at this point in their lifecycle, (so again get good quality seals if you can find them) |
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| Author: | 9YaTaH [ Mon Aug 28, 2017 10:06 pm ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
So... DOT3, DOT4, Super DOT4, DOT4+ and DOT5.1 are all Glycol based. The differences are in viscosity and boiling point and 5.1 is not hygroscopic like the others...fine for longevity of some components but not so for others... DOT5 is silicone based. |
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| Author: | Pd46 [ Tue Aug 29, 2017 12:58 am ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
9YaTaH wrote: The differences are in viscosity and boiling point and 5.1 is not hygroscopic like the others... DOT 5.1 is glycol based, and is hygroscopic. DOT 5 is silicone based and not hygroscopic. Sent from my ASUS_Z017DA using Tapatalk |
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| Author: | rossco_j [ Tue Aug 29, 2017 12:39 pm ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
Interesting document.... THE GREAT DOT BRAKE FLUID CONTROVERSY 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: 1. Fluid compatibility with the brake system rubber, plastic and metal components. 2. Water absorption and corrosion. 3. Fluid boiling point and other physical characteristics. 4. 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. |
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| Author: | Phil 850 [ Tue Aug 29, 2017 9:44 pm ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
Nice to have the BS separated from the facts. Thanks Rossco |
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| Author: | drmini in aust [ Tue Aug 29, 2017 10:27 pm ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
That's a damned good read, no BS. Mods, can we make it a sticky somewhere please? |
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| Author: | Hobson [ Wed Aug 30, 2017 8:56 am ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
The most interesting thing out of that I find would be the notes on the system flushing. |
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| Author: | FNQ [ Wed Aug 30, 2017 9:37 am ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
For track day or racers wanting the higher boiling points ( and mostly all DOT 4 or equivalent) here is a link to a recent british article http://trackdays.ie/best-racing-brake-fluid/ ( more of a list of product specifications in one spot rather than known recommendation) I would place Penrite Brake 600 ( a dot 4 plus) in this list also. any others out there, maybe in bike land? Interesting about the once going to silicon stick with it thoughts Also interesting in the good read article about the mini bleed before each session,,,,,, always good practice, but i had often thought it was more to release air when the seals dont quite keep up with the brake action ( or the little slave cup spreader isn't working perfectly)...,, but maybe it is the moisture? Excellent article |
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| Author: | minimans [ Wed Aug 30, 2017 10:27 am ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
I've never liked or recommended silicone based brake fluids, The fact that it does not absorb moisture but that it settles out in one spot is a hidden danger, as it will rot through the pipe at that one position. I have always used Castrol LMA in road cars with zero problems. In my own cars I use Rolls-Royce 363 brake fluid. don't know if it's any better or not it's just something I've always done since being an apprentice and using it in our race cars of the time. the ONLY advantage of silicone fluid to me would be it's lack of paint removal! It still needs to be flushed through the same as DOT 4/5/5.1............................ |
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| Author: | simon k [ Wed Aug 30, 2017 12:51 pm ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
'tis a good read, makes me not want to go anywhere near silicone fluid this bit doesn't add up... Quote: 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. ... 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. the bleeders are at the top, the water is at the bottom... if there's water in the caliper/piston, cracking the bleeder won't move the water |
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| Author: | winabbey [ Wed Aug 30, 2017 12:58 pm ] |
| Post subject: | Re: DOT5 silicone brake fluid problems.. |
drmini in aust wrote: That's a damned good read, no BS. Mods, can we make it a sticky somewhere please? Done. I did some formatting and posted it in the How To folder here - viewtopic.php?f=26&t=95967 |
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