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DOT3 or DOT5 brake fluid?

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  • DOT3 or DOT5 brake fluid?

    I am in the process of finishing my "upgrade" to bigger brakes and had a brake fluid question. I've replaced everything except the metal lines and the master cylinder... They seem to be in pretty good shape. Should I stick with DOT3 fluid or begin using DOT5 now? And why?

    Thanks.

    1951 Commander Starlight Coupe (aka "Stella")
    www.bulletshots.net

  • #2
    If you are using the car on a regular basis then stick with DOT3/4, if it is in storage for any length of time (5 mo or more) and you are in a seasonal climate then DOT5. This is my opinion from personal experience. My Hawk over a period of 4 years had the DOT3 fluid turn to gel in the wheel cylinders. I have had DOT5 for over 7 years and never a problem. This is always a hot topic and I am sure there will be a lot of discussion on this. There are a lot of opinions, as you will soon find out.

    Dan White
    64 R1 GT
    64 R2 GT
    Dan White
    64 R1 GT
    64 R2 GT
    58 C Cab
    57 Broadmoor (Marvin)

    Comment


    • #3
      Your question really is one of those ones that will get different answers from different people, I can only tell you what I do.

      I use a good quality DOT3 and change it every other year or so. Valvoline Synpower is supposed to be good, and it's easily available at your FLAPS. ATE Super Blue is good too, as is the Ford heavy duty fluid. I do this for several reasons:

      1) while DOT3 is hygroscopic and DOT5 is not, water can still get into your system making regular flushes necessary. And while DOT3 mixes well with the water, DOT5 will let the water pool in the lowest point in the system, practically ensuring that your wheel cylinders (and master cylinder, if it's under the floor) will rust if it's not flushed regularly.

      2) If you have a vacuum booster, if it goes bad it will suck brake fluid into the engine. This is not a problem with DOT3, it will just make lots of smelly smoke. DOT5 however is silicone, and when burned can create abrasive silica which is not good for your rings.

      3) DOT5 is slightly more compressible than DOT3 creating a slightly softer pedal feel. Also in difficult to bleed vehicles, DOT5 can hold small bubbles in suspension.

      4) DOT5 has been rumored to gum up pressure type brake light switches, although I have no experience with this.

      5) DOT3 is available at every FLAPS should you need to do a roadside repair; DOT5 maybe not.

      That said, there's lots of people using DOT5 for valid reasons, mainly because it is not hygroscopic, therefore if changed regularly will protect your brake system well - and also it has a higher boiling point than most DOT3s although this is not so true anymore.

      nate

      --
      55 Commander Starlight
      62 Daytona hardtop
      http://home.comcast.net/~njnagel
      --
      55 Commander Starlight
      http://members.cox.net/njnagel

      Comment


      • #4
        While DOT 3 my be hydroscopic, if you provide regular maintainance, this isn't a problem. Simply flush the system every so often.

        ---------------------------------------------------------------------------------------------------
        Tom - Sterling Heights, MI

        Ancient Chinese Proverb: "Injection is nice, but I'd rather be blown!"

        1964 Studebaker Daytona - Laguna Blue, Original 4-Spd. Car, Power Steering, Disc Brakes, Bucket Seats, Tinted Glass, Climatizer Ventilation System, AM Radio (136,989 Miles)
        Tom - Bradenton, FL

        1964 Studebaker Daytona - 289 4V, 4-Speed (Cost To Date: $2514.10)
        1964 Studebaker Commander - 170 1V, 3-Speed w/OD

        Comment


        • #5
          Eman,

          You have picked one of those questions that will generate a lot of 'back and forth', maybe second only to the 'stude engine or brand x engine' posts<G>!

          N8 has made some really good points. Read them over closely.

          My comments: I have used DOT 5 in my '64 Lark (approx 10 years) and my '55 pickup (approx 15 years). I have had no problems at all with the DOT 5 fluid. Yes, as N8 indicates, it is slightly compressive, but that has not caused me any noticable problem.

          A couple of suggestions if you are going to use DOT 5:
          1) Start out with good brake system components - new (or rebuilt) wheel cylinders, new hoses, new (or rebuilt) master cylinder, and new metal brake lines unless yours are perfect. (Remember, they may look great on the outside, but you can't see the inside of the brake lines.......!) If you reuse the metal brake lines, flush them out really good with alcohol or similar, and then blow them out real good with compressed air.
          2) DOT 5 will leak out of places where DOT 3/4 will not!! All connections must be in excellent shape. Use new copper washers where these are required.
          3) Add some sort of tag to the master cylinder, denoting that this car has DOT 5 fluid. If you have a lot of different cars (like me<G&gt and your mind is as forgetful as me<G>, believe me you will forget which car has which brake fluid!! Also, if someone else (spouse, etc) drives your Studebaker, and happen to need the fluid topped off, etc, the place will NOT ask what kind of brake fluid is in the car.

          Bottom line, if you flush/replace the DOT 3/4 fluid every so often, and the car is used alot, it is fine. If your car sits alot without being driven (like mine), consider the DOT 5.

          Paul
          Paul
          Winston-Salem, NC
          Visit The Studebaker Skytop Registry website at: www.studebakerskytop.com

          Comment


          • #6
            I'm with Paul on this. And frankly, I still have had anyone prove to me, exactly HOW Silicone - which is a very effective moisture repellent - is gonna allow water in your brake system unless you happen to have the master cylinder cap off and accidentally tip over your bottle of Evian in the course of adding fresh fluid.

            DOT 3 on the other hand, IS a water-sucking son-of-a-gun. And that moisture CAN migrate thru the whole hydraulic system, causing rust and deterioration of the fluid's properties - to the point of congealing at the very worst. That worst case scenario usually only occurs over long periods of storage.

            That said - I'm running both types in my Studes. The Transtar and the ragtop have silicone and the wagon I just redid with DOT 3. Why Dot 3? Like me, it's cheap![:0]

            I HAVE had encounters with DOT 5 where it fritzed the pressure type brake lite switches (the kind your 51 uses), so I've engineered mechanically-actuated switches when I've made the switch to DOT 5. It isn't hard to do. Ron Francis Wireworks offers a silicone-tolerant type pressure switch too. That might be the easiest way to go.

            My reasons for using DOT 5 before was so I WOULDN'T have to worry about corrosion or other problems over time. And thruth be told, that strategy's worked so far. As Paul intimated tho, silicone WILL find the slightest way out if it can. My Hill Holder's bleed screw leaks a drop every few weeks even tho I've tightened it numerous times. It's such a small leak that I don't worry about it any more.

            As has also been said, there's enthusiasim for both schools of thought on this subject. Performance-wise, I seriously doubt you can tell the difference. So it boils down to which argument you think has more merit!

            Miscreant at large.

            1957 Transtar 1/2ton
            1960 Larkvertible V8
            1958 Provincial wagon
            1953 Commander coupe
            1957 President 2-dr
            1955 President State
            1951 Champion Biz cpe
            1963 Daytona project FS
            No deceptive flags to prove I'm patriotic - no biblical BS to impress - just ME and Studebakers - as it should be.

            Comment


            • #7
              N8N said, "DOT5 is slightly more compressible than DOT3 creating a slightly softer pedal feel. Also in difficult to bleed vehicles, DOT5 can hold small bubbles in suspension."

              This sounds like an advantage for those like myself who are planning to switch their front brakes from drum to disc, but without a power booster. I've heard the brake feel becomes hard when you make that change, and the DOT 5 may therefore help soften the feel.


              1955 1/2 Ton Pickup

              Paul Simpson
              "DilloCrafter"

              1955 1/2 Ton Pickup
              The Red-Headed Amazon
              Deep in the heart of Texas

              Comment


              • #8
                I think some of the comments on DOT5 are myths and urban legends . I have never felt this soft pedal feel and like Mr. Biggs this idea that water can collect in the system, is bunk. DOT5 is NOT hydroscopic so why will water be attracted to the brake system, unless it is intentionally put there. I did not have any problem in bleeding the brakes either. Again, I have had DOT5 for over 7 years in my GT with power disc brakes and there have been no problems and the pedal feel is just fine.

                Dan White
                64 R1 GT
                64 R2 GT
                Dan White
                64 R1 GT
                64 R2 GT
                58 C Cab
                57 Broadmoor (Marvin)

                Comment


                • #9
                  I think water can enter via the master cylinder. The master cylinder cap is low and in the water spray and splash from the road. The caps are vented.

                  Comment


                  • #10
                    I suppose this is a possibility, but I think it is a stretch and if this is a problem with DOT5 it is an even bigger problem with DOT3. It is not a problem on GTs with disc brakes since the reservior is on the firewall and the vent tube runs down to the MC for the fill, and also with the Avanti and later Larks with firewall mounted MC.

                    Dan White
                    64 R1 GT
                    64 R2 GT
                    Dan White
                    64 R1 GT
                    64 R2 GT
                    58 C Cab
                    57 Broadmoor (Marvin)

                    Comment


                    • #11
                      Thanks for all the responses. I didn't mean to open a can of worms. I'm still not 100% set on it, but I'm leaning towards the DOT3 for now.

                      1951 Commander Starlight Coupe (aka "Stella")
                      www.bulletshots.net

                      Comment


                      • #12
                        We always used the dot 5 and never had any trouble. We always change over to dot 5 because the 3 is so nasty. It ruins the paint and stinks. For best results I'd go with the dot 5. Just make sure the system is completely cleaned with alcohol.
                        [img][/img]

                        -Home of John Studebaker-

                        Comment


                        • #13
                          In regions that suffer lots of humidity, some of that humidity will eventually find its way into brake systems. DOT 3 is designed to be hygroscopic to evenly disperse moisture through the system. This is desirable, preventing moisture from pooling in one spot and rusting or freezing in winter.

                          As the moisture in the system increases it will eventually start oxidizing the system from the inside. For this reason, and to minimize dirt and crud, the system should be flushed from time to time.

                          DOT 5 will not evenly disperse the moisture. If your climate is arid this is not a concern, though dirt and crud is.

                          If either fluid was hydroscopic, it would be able to see above the surface when submerged at great depths. That's why DOT 3 is hygroscopic, not hydroscopic. Submarines have hydroscopes, DOT 3 has hygroscopic properties. Somebody stop me!!
                          "All attempts to 'rise above the issue' are simply an excuse to avoid it profitably." --Dick Gregory

                          Brad Johnson, SDC since 1975, ASC since 1990
                          Pine Grove Mills, Pa.
                          sigpic'33 Rockne 10, '51 Commander Starlight, '53 Commander Starlight "Désirée"

                          Comment


                          • #14
                            You are right it is hygroscopic not hydroscopic, my mistake! Stude 4x4 I had forgot about the paint issue. I am paranoid about getting brake fluid (DOT3) on my daily drivers when I add fluid. It is easy to get a drop on and not realize it!

                            Dan White
                            64 R1 GT
                            64 R2 GT
                            Dan White
                            64 R1 GT
                            64 R2 GT
                            58 C Cab
                            57 Broadmoor (Marvin)

                            Comment


                            • #15
                              Yeah don't learn the hard way like me. Dot 3 eats paint. And it hurts like a BEAR when you get it in your eye.

                              -Home of John Studebaker-
                              http://community.webshots.com/user/Stude4x4

                              Comment

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