Dot 4 synthetic or Dot 4

Discussion in 'Touring Models' started by Duke16, Oct 11, 2009.

  1. Duke16

    Duke16 New Member

    Question for brake fluid experts.Would like to flush brake system and have I pick up some Dot 4 Synthetic to do the job.Anyone see a problem with this fluid or should I stay with Dot 4 glycol base fluid as the bike has this from the factory. 2007 ultra classic non abs.:D


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  2. HarryB737

    HarryB737 Junior Member

    I don't know about DOT 4 synthetic, but what ever you do... do NOT use DOT 5 where DOT 4 has been. It has a different chemical make-up & will clog your calipers big time... when the two mix !!
  3. springer03

    springer03 Active Member

    DOT 4 polyglycol ether-based brake fluids are hygroscopic, which means they absorb water easily and hold it in suspension Dont think the syn will do this. moister i.e. water heaver than fluid will sink to lowest part of the system... jmo get some more post before you decide. :cheers
  4. glider

    glider Veteran Member

    Stay with the Dot 4 glycol base to avoid any problems. It's tried and true and down the road it will not confuse anyone working on the bike.

    NEWHD74FAN Experienced Member Retired Moderators

    DOT ratings for brake fluid are strictly temperature rating...which is why there is such a problem with actual TYPE of fluid and all the compatibility issues!

    As Glider says, ethylene glycol based brake fluids have been standard fare for years...only problem was it absorbed water over time which lowers boiling point and water settling to the lowest parts of the braking system causes rust/corrosion. Silicone based fluids were introduced in racing circles for their temperature advantage (hence DOT 5) but was not compatible with ANY of the ethylene glycol versions, and though "inert"...silicone is a contaminant that does not degrade or clean up well in the environment (like teflon)...some military specs even require silicone NOT be used in their equipment).

    Since "Synthetic" is all the rage now due to it's purity (being chemically all man made with no impurities) it is a great advertising/marketing ploy...but compatibility to existing fluids I doubt has been researched fully over YEARS of I would stick with conventional as the "--jury is still out". Just remember the problems with MTBE, alcohol and other additives added to your fuel in the interest of stretching "YOUR" fuel (it actually expanded the oil companies' wallets)...and 10 years later we have pollution that leaches into ground water, turns your fuel lines and fiberglass tanks to mush...JMO but I would just wait and see. :no
    Last edited: Oct 13, 2009
  6. Duke16

    Duke16 New Member

    Thanks for the reply's

    I am going to stay with Dot 4 gycol to be safe.

  7. hoggy25

    hoggy25 Active Member

    I'd just use the stock HD dot 4 for this as you can be sure it is compatible. It's not like you have to change it very often so the slight cost difference should not really be a big deal.
  8. Duke16

    Duke16 New Member

    I am doing a flush of front and rear. How much fluid should I buy.

  9. Jack Klarich

    Jack Klarich Guest

    Buy as much as u can use at one time as soon as u open a can of brake fluid the clock is ticking on it taking on moisture moisture is what causes brake fluid failure all brake fluids are hydro scopic except silicone fluid H D had problems with dot 5 crystalizing so the switch to dot4 I work in the Auto industry we use dot 4 daily with no problems a few trucks by GM have used dot 5 with mega problems be safe