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An insight into Brake Fluid

Discussion in 'BENDIX – Put your foot down with confidence.' started by bendix, Jun 20, 2016.

  1. bendix

    bendix Member

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    Bendix provides an insight into the importance of Brake Fluid
    Most of us probably drive our cars 15,000 to 20,000 kilometres a year and during that time we would have probably changed our engine oil, had our coolant levels checked, wiper blades replaced and maybe even had our brake pads and rotors checked?
    Have we ever thought how many times we actually step on the brake pedal over that period when taking our car for a drive? And have we given any thought to our car’s brake fluid at all?
    Do we know that our car’s brake fluid also needs to be checked and replaced regularly? Many OEMs and maintenance experts recommend that we replace our brake fluid at least every two years. Do we know why? Please read on.
    [​IMG]
    What is brake fluid?
    Brake fluid is basically a hydraulic fluid that actuates our car’s brake system when we step on the brake pedal. As a fluid that transmits force, an important property of the brake fluid is that it should be non-compressible so that it effectively transmits braking force to the wheels at all times. As brake fluids are exposed to very high temperatures during braking, these should have very high boiling points so that they remain incompressible even during extreme braking.
    America’s Department of Transportation (DOT) has set the pace in putting in place a standard for brake fluids. In the industry, we have adapted two main standards – DOT 3 and DOT 4. There are other types of brake fluid in use but most vehicles use either DOT 3 or DOT 4 brake fluid so we will stick with these two for purposes of this discussion. The table below shows the boiling point standards. Note that the Australian standard has a more stringent boiling point requirement than the internationally accepted American DOT standard. Note that the Bendix line of brake fluids conforms to both the DOT standards and the Australian standards and in fact exceed these standards by a wide margin.
    [​IMG]
    Brake fluid is a glycol-based fluid that remains fluid even when freezing and remains effective as a hydraulic fluid even at high temperatures. It is expected to work in freezing winter and in extremely hot summer months. It is a versatile fluid that does its job in all temperature extremes. However, brake fluid by nature absorbs moisture from the atmosphere through the microscopic pores in brake lines and through the small vent in the reservoir. In fact brake fluid begins to take in moisture the moment you pour it into your brake system.
    After a year in service, brake fluid would have absorbed about 2% water and will have progressed to 3% water after only 18 months. These figures would be a lot higher in places that are humid and wet. Moisture in brake fluid decreases its boiling point – 2% water will reduce the brake fluid’s boiling point by 75°C. The boiling point drop becomes more pronounced as more moisture is absorbed.
    Moisture contamination heightens the risk of brake failure especially during extreme braking conditions like driving downhill or in constant stop and go in heavy traffic or when carrying heavy loads. Constant braking transmits a lot of heat to the brake fluid from the pads and rotors. If a considerable degree of moisture were present, these would easily boil off and form vapour which is extremely compressible and this is when the pedal starts feeling spongy and the brakes would not apply at all!!
    This is the reason why there have been many cases of brake failures even if the braking systems were found to be mechanically in order. In fact, the brakes worked perfectly again after the system has cooled down and the vapour has condensed.
    Presence of vapour in the brake fluid also affects the performance of the Anti-lock brake systems (ABS). The ABS pulsates about 15 times a second and the brake fluid’s viscosity is an important factor for the proper operation of the ABS. The presence of moisture and/or vapour in the brake fluid alters its viscosity characteristics and will result in improper operation of the ABS.
    DOT 4 and DOT 3 Brake Fluids
    From the table above, we can see that the main difference between DOT 4 and DOT 3 brake fluids is that DOT 4 brake fluids have higher minimum dry and wet boiling points – and this is why majority of car makers recommend DOT 4 brake fluid over DOT 3 as it provides an extra margin of safety. Both are made from glycol ethers but DOT 4 brake fluids are added with borate esters to give them that improved dry and wet boiling points. DOT 4 maximum viscosity specifications are also slightly higher than that of DOT 3.
    Often not mentioned is the effect of the different DOT 4 formulation on the brake fluid behaviour. DOT 4 absorbs moisture at a slower rate than DOT 3 but is more susceptible to suffering a drop in its boiling point. Typically a DOT 4 brake fluid will suffer a boiling point drop of 50% once it takes in 2% moisture while a DOT 3 brake fluid would only lose 25% of its boiling point at 3% moisture contamination although it takes in moisture at a faster rate. This suggests that DOT 4 brake fluids offer more stability and safety for longer but would need to be replaced at the recommended OEM intervals before it suffers a substantial drop in boiling point.
    Some cars have had their brake systems designed before DOT 4 brake fluid was introduced. Their hoses, which inner linings are made of SBR rubber, were found not to be compatible with some DOT 4 formulations in a laboratory setting – possibly those with very high borate ester content. In a report, it is claimed that DOT 4 brake fluid permeates the inner lining and then reacts with the outer PVA reinforcement braiding producing a viscous liquid which could build up between layers of rubber and makes the hose considerably weakened. Attempts to reproduce this problem in real life conditions have proven to be difficult though. Some Australian vehicle manufacturers may still use brake hoses made with SBR hence their recommendation to stick with DOT 3. Most vehicle marques today use a different rubber (EPDM) in their brake hoses which is much less subject to permeation. Most car makers have taken the view that the extra safety offered by DOT 4 more than outweighed the miniscule risk of hose failure caused by the reaction described above.
    For more information free call the Bendix Brake Advice Centre on 1800 819 666 or +61 3 5327 021 (8am-5pm Monday to Friday EST),
    e-mail us at: brakeadvicecentre@bendix.com.au
    or visit our website by clicking here
    - http://motorculture.com.au/blog/2016/06/20/an-insight-into-brake-fluid/
     
  2. markholland

    markholland hotrotor.17

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    Great Information,
     
  3. Skydrol

    Skydrol Active Member

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    One thing that I always wonder about brake fluid and moisture. How the moisture gets in the brake system? Is a close sytem, the cap has a rubber piece that expands to take the place of the fluid as it goes down. Also, you can check on most cars the fluid by the reservoir (clear); you hardly open the cap. If it has an open end will be obvious (leaks).

    Can someone shine some light on this?
     
  4. Zeke Topanaga

    Zeke Topanaga New Member

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    It gets in regardless just pull the top off the cap and you may see slight water mist in the cap at times and your brake fluid container if you brake the seal open it will draw in water.
    Remember it's only a little bit of water that makes a big difference.
    A mate got his car serviced by Holden when it was 2 years old and they changed the brake oil, and week or 2 later he went straight through across a highway as he could not stop, because the peddle went to the floor due to the fluid boiled because of crap low grade brake oil was the problem and maybe it contained some water.

    The heat and the cooling makes for pressure to drawer water into the system, just like professor Miller once on TV showed with a Hard boiled egg that got sucked into a milk bottle.
     
  5. strgas

    strgas GRA = REAL HP

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    sounds like your mate got a friday special brake bleed , thats when they change out the fluid in the res only from an open 20 litre drum sitting in the workshop coz the snot nosed 16 yr old apprentices were to lazy to put the cap back on and was worried about losing his bouns if was over time on the job ..... $$$$$$$$$$$$
     
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  6. Skydrol

    Skydrol Active Member

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    Heck.... I rather do that job myself. Replaced mine while changing pads and rotors, just with a hand vaccum pump. Next time, will borrow the electric pump from the part store; just easier that way.
     
  7. Zeke Topanaga

    Zeke Topanaga New Member

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    True ! and that's what I thought.
     
  8. Zeke Topanaga

    Zeke Topanaga New Member

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    Same here, I gave up on anyone touching my brakes back in 1985 only because I thought they knew better than me, big mistake listening to them morons back then, I came in with brake rotors all black and blue from brake fade, it was my first 5.0L V8 and I asked about going for metal king pads and got the no no no they will destroy your rotors they are no good, they were full on against it, total toss pots!
    No wonder so many people got killed from 1968 on, in a quick car, I call it pre meditated murder ! in my books. for f sake ! it was only from about 2010 that brake shop people started to wake up to reality.
    Maybe it was the visual trend of having Brimbos that woke some of the twerps up.
    I have had such clowns say that the reason why manufactures and people are going for bigger wheels is for improved fuel economy, f ing BS ! it is, stupid old c---s.

    My wife had new pads fitted on her 1997 VS commodore in about 2001 and I give them a test out at 110KM/H to dead stop, no ABS mind and I could not lock them up at all on the first try, this mob fitted bendix standard type brand pads and the original pads are bendix but of a higher grade than bendix standard type, I informed the brake shop and it just went in one ear and straight out the other, f heads ! so I just replaced them with another set that I pulled off my new VS when I first bought it and replaced for Bendix Ultamate and all was fine for her car.
     
  9. strgas

    strgas GRA = REAL HP

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    I have worked in anumber of workshops and stealaships were quick and efficient workers are treated well but those workers who do the job right and with care are given less likable treatment coz they are seen as slow lazy workers , different story when cars come back with failing brakes or worn out inner bearings blocked filters due to short cuts taken by these so called quick and efficient workers taking short cuts.

    I guess dollars are worth more than repeat bussiness or loyal customers or loyal workers too .
    To the service managers who sit in their offices and think they know whats going on in their workshops get real , theres more than just the bottom line .
     
  10. Skydrol

    Skydrol Active Member

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    Usually I stick to OEM brands. On my VE, went with AC Delco Professional (pad and rotors). The original set wore out at around 90,000 miles; so why not? Replaced the fluid with Valvoline Synthetic DOT 3 and 4. Went through quiet a bit, I think it was about a litre, considering flushing and refill. To my surprise, one of the rear calipers had an air pocket. Next time I will use an electric pump.

    I believe is good to go for another 90,000 miles.
     
  11. strgas

    strgas GRA = REAL HP

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    electric pump ?????????? many years flushing and bleeding brakes never seen or used an electric pump , vacum bleeders or pressure bleeders yes or just had a second person pump the brake to push the fluid thru .. also can gravity bled most systems without a problem .
     
  12. Skydrol

    Skydrol Active Member

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    Used a manual vacuum pump. The type you use for vacuum checks. Went to the caliper, open the bleeder valve and connected a hose. Done it on 3 cars and never had an issue; is just tiresome. I was thinking next time, do it the same way with an electric vacuum pump. The type that is used to evacuate and vacuum test A/Cs. Pulls 30 in/hg, same as the hand pump.
    Need to keep en eye on the reservoir level. If you trap air... you get the idea.a
     

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