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5.1 brake fluid

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  • Brakes: 5.1 brake fluid

    Hello all,
    I’m thinking of switching to DOT 5.1 brake fluid in my ‘50 Champ. I was wondering if anyone else had done so and their experience? Currently, I use DOT 3 with no issues ( it’s not a daily driver). I know it’s compatible with DOT 3&4 and wouldn’t require a replacement of all hoses, wheel cylinders and MC. It seems like the best option unless doing a full retrofit and going with DOT 5. Are there any cons to using 5.1?

  • #2
    I haven't heard of a 5.1 ? What is it made of ? Ed


    • #3
      It really should have been called DOT 4.1, as it's glycol-based, just like DOT 3 and 4, and is NOT silicone-based like DOT 5. It has a higher boiling point than DOT 4..
      Skip Lackie


      • #4
        Come-on guys...

        Jim -
        There's no such thing as DOT 4.1 brake fluid..! You were correct in your initial comment/question, 5.1.
        There's really no benefit in your application. Higher boiling point is the main attraction to the 5.1 fluid. Unless you are road racing or maybe living in the mountains, DOT 3 or 4 is more than enough.
        Many SCTA type road race / solo 1 and 2 guys even just use the grade 4 because of its boiling point isn't enough lower than the 5.1, and they change the fluid after every race anyway. So they actually save a few bucks using the DOT 4 on the track.

        And yeah, though some may disagree, grade 5 (silicone) fluid is NOT for me. Nore is it for any performance driving as, again, despite some, provides a spongy, or not firm pedal feel.
        Although, it does not hurt paint, which is mainly behind its development years back. Guys with high end paint work needed a fluid that would not ruin their paint work.

        A simple lookup in Google doubt reinforce my comments.



        • #5
          Gave up on silicone fluid decades ago. Now I use Valvolene synthetic fluid; I've been very happy with it. It is not as hydroscopic as DOT3 and it does not soften rubber like silicone. Also had a lot of brake light pressure switch failures with silicone fluid.


          • #6
            Good to know, maybe I’ll stick with the DOT 3


            • #7
              UPDATE: two items:
              #1 .the DOT 5-1 is much thinner (less viscocity) than DOT 3 or 4 in order to react more quickly to anti-lock braking conditions (rapid on-off of brake system).
              #2. A good reference on the differences and application of different DOT types can be found at the "Safe Braking" site.

              Years ago , somewhere, an article stated that 5.1 was developed for automatic/antilock braking systems in that it is a different consistency so to be able to react faster to the ABS system.
              Anyone know if this is a real difference?

              Last edited by Paul Keller; 08-02-2021, 12:15 PM.


              • #8
                DOT 5.1 v DOT 5 -tomato? Regardless if you use DOT 5 you may want to put a few drops of the DOT 3 in the brake switch to have it live longer.
                Rob in PA.


                • #9
                  Not sure why using the fluid to light the stop-lamps ever made any real sense, particularly after WWII, except that safety was never a concern. GM didn't use them, and thus we have a handy big switch to use in our cars under the brake pedal.

                  It does seem a good idea to switch to a mechanically-activated brake light switch with silicone brake fluid. But I believe this is also true with regular brake fluid. Those hydraulic switches fail with either fluid in them. That said, I've added a mechanical GM switch only to my '51 Commander Automatic (dual cylinder upgrade with silicone), but just put DOT-3 and the stock switch back on my '51 Champion with a single-circuit system. I needed to get it finished to move the car.


                  • #10
                    I I'm going with ES16. Even though it's designed to work with anti-lock brakes, a very good improvement for dot 3, 4, 5.1 Click image for larger version

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