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should i keep dot5 in the brake system?

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  • Brakes: should i keep dot5 in the brake system?

    PO switch it to DOT 5, i need to be changing brake lines and front wheel cylinders to upgrade my "drum" brakes, but this DOT 5 stuff has me concerned, i believe Dot 3 is fine for decades.

    how do i get rid of it from the rear wheel cyli Click image for larger version

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  • #2
    Not sure I agree with your conclusions. Have had DOT 5 in my Studes and other cars for ~40 years in humid DC with no problems. And many car manufacturers and mechanics now recommend flushing DOT 3 every 3-5 years. Dot 3 absorbs moisture and promotes rust. Dot 5 does not. The problem with Dot 5 is that water can collect in low spots in the brake lines and cause rust in those spots.

    In any case, converting from one type to another usually requires flushing the whole system with a solvent like alcohol or acetone and then blowing it dry with compressed air. All rubber parts in the M/C and W/Cs should be replaced.
    Skip Lackie


    • #3
      I would not use acetone. Pure alcohol would be best as it would have no adverse effect on rubber. I like Valvolene synthetic fluid. It is far less hydroscopic and doesn't eat brake light switches like silicone. Like Skip said; disconnect the lines and remove the bleeder screws, flush , blow out the system, let it set a day (open) to let any left over alcohol evaporate, hook the lines back up. You might want to invest in "Speed Bleeders" to save your $ from the cuss jar. You can buy a brake fluid tester that will tell you if it is time to change brake fluid (seems like $10 well spent. (Has any one used "Heet" to flush brake lines)


      • mw2013
        mw2013 commented
        Editing a comment
        i do have a speed valve that connect to the end of a hose, i crack the bleeders and the check ball valve allows 1 way exit of fluid and no air on the return.

      • Skip Lackie
        Skip Lackie commented
        Editing a comment
        I suggested acetone only when converting from one type of brake fluid to another, and then also said that all rubber parts should be replaced (to get rid of any old fluid that soaked in). I like acetone for this application because it will flush out water (chem labs use it for just that purpose) and because it evaporates almost instantly, leaving the brake lines completely dry inside.

    • #4
      many of my flaps out here don't carry this stuff, and I am in Los Angeles, i was bale to buy a small bottle when i first got the car for topping off; but never had to , from a practical standpoint, most drivers don't even know to change Dot 3 on their daily drivers,

      and 20 year old or older brake fluids is still stopping cars all over the place, i know my 2003 chevy s10 got 20 year old stuff in it, only from brake work does it have some new fluid to dilute the old, not to say it a good thing, but that is how it is.

      additionally i read that dot 5 compresses more so the drum brakes already needing all the help it can get is not getting it in this area.

      i think i am going to swap it out, can i use 70% alcohol?

      I dont know how good a job the PO did in converting over to dot 5 in the first place, i am sure thee are trace amouts of dot 3 left in the system, as you can tell by the picture that brake hose has got to be 62 yearold.

      all said i have a firm pedal right now and the brakes stop straight at any speed, just looking to clean it up and upgrade it a little


      • #5
        If it already has DOT 5, I would definitely not change it. But then again, if it already has DOT 3 or4, I would not change over to DOT 5 either. As for DOT availability, it's as common as DOT 3/4. If all else fails, go to a Harley dealer, as Harleys have been using DOT 5 since the 1980s.

        ALERT: NEVER mix DOT 5 with 3 or 4. Trust me, just don't. If you decide you just gotta switch from DOT 5 to 3, you must disassemble the entire system and clean ALL traces of the old DOT 5. Major hassle to switch it, in either direction, and no measurable difference between them. I have been using DOT 3 for decades, but also traded into a couple of Studes that had been converted to DOT 5, so I left it alone. I still have a quart bottle of DOT 5 leftover from the last Stude I had that a PO had changed to DOT 5. If you lived closer, I'd give it to you. Difficulty finding DOT 5 is a very poor excuse for converting to DOT 3, IMHO. It is at least 100 times easier to find DOT 5 than it is to convert to DOT 3. LOL


        • #6
          idk, how well they cleaned the system to convert it to dot 5 in the first place, look at the rubber brake hose, they didn't bother to change that... i am installing new braided steel hoses and front wheel cylinders, maybe i will try to clean it as best as possible and take my chance

          i hate the thought of someone else after me topping it off with dot 3 and then what? and i feel trapped having to stick with dot 5, all my cars use dot 3, i'd rather have dot 3 across the board, that is just me...


          • #7
            Synthetic is compatible with DOT3 so you wouldn't have to worry 'bout that either. I'm not sure what would happen if you mixed 3 and 5. Would it be classed as a wmd? I do know that it is a no-no. Someone tell us dummys why this prohibition.?


            • #8
              NO, No , No. Do not use 70% alcohol because it is 30% WATER.


              • #9
                Definitely keep the DOT 5 as it's an improvement and already there. DOT 3 is going back in time.


                • #10
                  this video shows the separation of the dot5 and dot 3 mixed, unsure if the po even got all the dot 3 out, i doubt it looking at the 60 year old brake hose



                  • #11
                    Suit yourself on going to the trouble of going backwards to DOT 3, but if say, if it ain't broke, don't fix it. Yes, replace the old rubber.
                    Mike Davis
                    1964 Champ 8E7-122 "Stuey"


                    • #12
                      Make sure you're talking about silicone-based DOT5 vs glycol-based DOT5.1. I don't see much DOT5 on shelves around here; it's almost always DOT3/4 or DOT5.1, and I believe they're all mixable with one another.

                      They really messed up the names with this stuff...


                      • #13
                        i keep reading the motorcycle crowd hates it, the go fast car guys hates it, to me it's just like GM dexcool, different for worse reasons, it's going away.


                        • #14
                          Mason I don't know why you have it in your mind that you have to change out your brake fluid, but it sure isn't evidence based. It shouldn't be such a hard call. In our collection we have two cars, and only two cars, in which I used DOT5. One of the two was done 45 years ago, the other 40 years ago. I have never had a bit of problem with either. They still have the same equipment in place that I used almost a half century ago. I have about 30 cars. I wish that I could say that the DOT3/4 equipped cars have been as easy to live with. The way I see it, most people don't keep their cars as long as I do-so it's hard to get a feel for the difference.

                          Forty five years ago DOT5 was just beginning to get some traction in the old car hobby. I didn't know that the difference was going to be as stark as it turned out to be. I have to be a believer I live with the differences every day.


                          • #15
                            spongy felling, hard to bleed, too many bubbles, compress-ability when hot, any water in system will boil away when too hot, and cause a lock up, any left over water in system will find it's way to bottom of brake parts and corrode them, no racing car or racing motorcycle use it; is some of the negative things i have read about it.

                            i will flush it OUT and report back, i want to have the best braking ability for my old fashion drum brakes and from what i read, dot 5 , albeit is relatively maintenance free, it is not optimal for stopping.

                            you have 30 cars, you are a wealthy man, my guess is some sit for long periods of time, not only do brake systems suffer when that happens, the whole car suffers, I drive my machines and i maintain them or they are gone.

                            50 years on the same brake fluid, is great, i think dot 5 is for people that just drive their cars or let them sit forever and not "maintain" them, many more cars on road that uses dot 3, 4 and 5.1. and to me that is proof Dot 5 does not have wide acceptance, for some reason. No one wants it, most of my flaps don't carry it and i live in the second largest city in the country.