dot brake fluid

delcol
delcol Posts: 2,848
edited June 2008 in MTB workshop & tech
sorry if this is a repeat thread

is brake fluid just brake fluid ie can you use any dot4.5 or 5.1 fluid in your brakes (avid juicy) i know you cant mix mineral oils and brake fluid,.

i have been told that brake fluid is just brake fluid so long as its numbers tally 4.5 5.1ect so can anyone clarify this for me so i dont fook my avids up when i bleed them.
thanks
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Comments

  • ratty2k
    ratty2k Posts: 3,872
    Provided the numbers match you'll be fine. You can put 5.1 in, but you have to makes sure you have got ALL the dot 4. whatever out of the system.
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  • nicklouse
    nicklouse Posts: 50,673
    http://www.bikeradar.com/forum/viewtopic.php?t=12534925

    scroll down.

    if you have a specific question ask it.

    EG: can i use X fluid in Y brakes?
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  • Splasher
    Splasher Posts: 1,528
    DOT stands for Department of Transport (in the US) and is a standard for brake fluid. There are 4 DOT standards: DOT3, DOT4, DOT5 and DOT5.1.

    Fluids of exactly the same DOT from different manufacturers can be mixed but different DOTs must not. DOT 5 and 5.1 have very similar performance but are a different fluid (5.1 is silicone based and supposedly less prone to moisture pick-up).

    So whatever your manual says, is exactly what you should use.
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  • nicklouse
    nicklouse Posts: 50,673
    Splasher wrote:

    Fluids of exactly the same DOT from different manufacturers can be mixed but different DOTs must not.

    sorry they are all mixable (except DOT5).
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  • Splasher
    Splasher Posts: 1,528
    Semantics Nick. Mixing brake fluids for someone who doesn't understand the consequences on the boiling points would not be advisable which is why I said "must not".
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  • dave_hill
    dave_hill Posts: 3,877
    Splasher wrote:
    Semantics Nick. Mixing brake fluids for someone who doesn't understand the consequences on the boiling points would not be advisable which is why I said "must not".

    Agreed. I wouldn't mix brake fluids in a car or motorbike system, so I don't see that a bicycle system is any different.
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  • tjm
    tjm Posts: 190
    dave_hill wrote:
    Splasher wrote:
    Semantics Nick. Mixing brake fluids for someone who doesn't understand the consequences on the boiling points would not be advisable which is why I said "must not".

    Agreed. I wouldn't mix brake fluids in a car or motorbike system, so I don't see that a bicycle system is any different.

    but isn't the point that dot 4 and 5.1 ARE compatible. Meaning that you can mix them without causing problems.
    The only difference being that Dot 5.1 has a higher boiling point. So, if you are worried, just use 5.1. If you had 4 before it won't make it worse! (or better either)
    In an emergency, if you can only get your hands on 4 then use it. You can always flush it through with 5.1 later. A few traces of 4 left in the system will do no harm.

    However, I agree with the point that you really should know what you had to start with. If it wasn't 4 or 5.1 then you will get into trouble.
  • Splasher
    Splasher Posts: 1,528
    Yup, the point is you can put fluid of the same basic compound but of a higher boiling point in. But trying to explain all of the permutations that are good, and all those that are not, also taking into account that DOT5 doesn't mix with anything else seemed a bit of a lengthy and risky process.

    I think for anyone not already familiar with brake fluid, the best advice is read the manual and use what is already in there.
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  • Rockhopper
    Rockhopper Posts: 503
    Most cars specify DOT4 so there is no harm in mixing DOT 5.1 if thats all you have and you want to spend the extra money!

    In terms of whats safe, DOT 3, 4 and 5.1 can be mixed, DOT 5 can't be mixed with anything other than more DOT 5.
  • Splasher
    Splasher Posts: 1,528
    Rockhopper wrote:
    In terms of whats safe, DOT 3, 4 and 5.1 can be mixed, DOT 5 can't be mixed with anything other than more DOT 5.

    It is not safe to mix DOT 3 in a system designed around DOT 4 or 5.1 and it is not safe to mix DOT 4 in a system designed around DOT5.1 as to do so would lower the boiling point of the fluid. Please be careful with your advice and consider that the OP is new to all this.
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  • RichMTB
    RichMTB Posts: 599
    Without wanting to join in the chemistry lesson.

    You can use any brand of brake fluid for your brakes as long as it matches the brake fluid type for your brakes. Just check your manual

    You can get a 250ml bottle of DOT 5.1 from Halfords for £3.99 or you can buy the "mountain bike specific" alternative for about £10
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