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Thread: DOT 5 Brake Fluid

  1. #1
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    DOT 5 Brake Fluid

    Am planning on flushing my brake system this weekend ( 93 K100RS w/ABS) and plan on converting over to DOT 5....any folks here done this ? I assume it is compatable.....

  2. #2
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    May have answered my own question....just found this analysis on the AAA web site...




    DOT 3 and DOT 4 fluids are called polyglycol fluids for the principal compounds used in their manufacture. DOT 5 fluids are all silicone based because only silicone fluid can meet the DOT 5 specs. No vehicle manufacturer, however, recommends DOT 5 fluid for use in its brake systems. Although all three fluid grades are compatible, they don't really combine if mixed together in a system. Therefore, the best general rule is to use the fluid type recommended by the carmaker, and not to mix fluid types in a system.

    CAUTION: Do not use silicone DOT 5 fluid in an antilock brake system. Operating efficiency will be reduced.


    Silicone DOT 5 fluid has some other characteristics that you should beware of. Silicone fluid compresses slightly under pressure, which can cause a slightly spongy brake pedal feel. Silicone fluid also attracts air more than polyglycol fluid does, which makes brake bleeding harder. It also tends to vaporize slightly just below its boiling point; and it will aerate from prolonged vibration. All of these factors mean that DOT 5 silicone fluid should never be used in an antilock brake system

  3. #3
    Registered User TRJeff's Avatar
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    Thumbs down Brake fluid

    Don't do it! Stay with the DOT 4 fluid and do the recomended changes. DOT 5 will produce a different some what spongy feel at the lever when compared to a fresh change of DOT 4 fluid. Also the BMW brake system ( Brembo) does not recomend using DOT 5.

  4. #4
    A bozo on the bus deilenberger's Avatar
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    Re: Brake fluid

    Originally posted by Jeff
    Don't do it! Stay with the DOT 4 fluid and do the recomended changes. DOT 5 will produce a different some what spongy feel at the lever when compared to a fresh change of DOT 4 fluid. Also the BMW brake system ( Brembo) does not recomend using DOT 5.
    I'd also suggest staying with a 'standard' brake fluid. Besides the problem with bleeding DOT5 (air doesn't flow in it like it does in standard fluid) - you'll never get the remaining DOT 4 completely out of the system.

    I'm sure you'll hear from a few people who have done it and love the DOT5 - but I tend to be conservative on things like brakes - I want them to work as designed.

    There is another standard 5.1 fluid - which is an organic fluid that is compatible with DOT4 - and has a higher boiling point (which is a factor of how much water can be absorbed) - but I've had good luck with ATE fluid - changed at least yearly. If you do regular fluid 'flushes' (where you're flushing the fluid through the system without ever introducing air) - your brake components will last a very long time without giving any trouble.

    Best,
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  5. #5
    Registered User HANSRUYS's Avatar
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    DOT 5 brake fluid

    The only reason DOT 5 emerged on the motorcycle market is in the early 70's
    when Harley Davidson started installing disk brakes on the FLH and their Superglide models
    they "brilliantly" placed the rear master cylinder between the engine and transmission
    (right next to the exhaust pipe)
    the police motors were the first to complain of brake fading under extreme temperature conditions,
    seems the brake fluid was absorbing too much heat and boiling,
    rather than redesigning this obvious "flaw" they opted for DOT 5
    because it has a higher "boiling point" and that is the only advantage it has,
    just because it has a higher "number" does not make it a better product.

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