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Brake shimmy/judder/vibration only after brakes are heated up at the track

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  • Brake shimmy/judder/vibration only after brakes are heated up at the track

    Recently went to Winmax W6 on my 1998 M3. I am running brake ducts.
    After one 20 minute session, for every session after (about 40-60 mins between sessions), my steering wheel shakes while braking. This is enough vibration to make me worry, this isn't mild vibration felt because my wheels are slightly off balance or anything. I should also note that wheels are balanced to 0, balancer was recently calibrated. Wheels don't wobble on the balancer while spinning. I balanced them myself. Also, I drive this from time to time on the street and it has zero vibration while braking, although this is street braking, not hard braking like at the track. My brakes never get mushy at the track (using motul 660).

    Anyone dealt with this before and remedied it?

    I installed new rotors (brembo blanks) when I switched to the W6.
    Previously I used the W6 and Carbo tech xp12. The XP12s would only vibrate near my last session on 90°F+ days and before my days of brake ducts.

    Any input would be appreciated!
    How can I do?

  • #2
    I've had this issue pop up due to 3 separate issues on my miata. Once it was because I was giving vendor rides at MRLS and was doing 3 hot laps and coming back into the pits to strap the next rider in. The lack of cool down laps and having to touch the brakes in the pits occasionally cause my rotors to warp. That, is likely not your issue.

    The other time this has happened is when I've had a wheel bearing/hub start with one foot in the grave. I've found that of the 3 front wheel bearing failures I've had, 2 of them would start to show signs of imminent death by getting thumpy when they got very hot. Basically towards the end of the session they would get hot and felt almost like a warped rotor.

    The last issue, which I feel may be your issue, was that when I was running a very aging set of carbotech's (XP10) and they would get down in material... they would get thumpy. I am not 100% sure this is a thing and I would speak to emilio about this. However I was experiencing what you describe and mentioning it at lunch to other miata people (eric and brett) and they mentioned that carbotechs can get thumpy when they are very low on material.

    Not 100% relate-able to your situation obviously because of a different car, but I just thought i'd mention a few possibilities to get the juices flowing.

    Comment


    • #3
      Shimmy judder vibration are all different things. Which is it? W6 has lower max heat rating than xp12. Is it possible you have judder from over heating the pads causing pad transfer issue and thus judder? A shimmy would be more like failing wheel bearings or rack play which could get worse with heat. A vibration is common with wheel tire issue. Some combos will balance fine but still vibrate because wheel is really out of round. You can feel 020" out of round and my grandma can feel 040 out of round. How much weight is needed to balance the wheel? If you got 2 oz round the wheel I will bet you are out of round. Also watch the tire monkeys. If they do not set the wheel width and a few other parameters the machine will default to static balance even if the wheel is spinning on their machine.

      Comment


      • #4
        Since Eric and I spoke about thumpy brake pads, I've have had what alcoholics refer to as a moment of clarity. I had been tossing my Carbotechs before they were worn past the center groove, but through random instances of timing and maintenance, I now think the main culprit was my front hubs.

        In the past, I had experienced vibration up front during braking and thought it was the worn pads and possibly runout in the rotors. It usually happened at the end of the season when I would service the bearings anyway, so I just figured it was the pads. The last race of last season, I discovered it's probably the bearings.

        In addition to what Carl said, check your bearings.
        www.TrackHQ.com

        Comment


        • #5
          Originally posted by fatbillybob View Post
          Shimmy judder vibration are all different things. Which is it? W6 has lower max heat rating than xp12. Is it possible you have judder from over heating the pads causing pad transfer issue and thus judder? A shimmy would be more like failing wheel bearings or rack play which could get worse with heat. A vibration is common with wheel tire issue. Some combos will balance fine but still vibrate because wheel is really out of round. You can feel 020" out of round and my grandma can feel 040 out of round. How much weight is needed to balance the wheel? If you got 2 oz round the wheel I will bet you are out of round. Also watch the tire monkeys. If they do not set the wheel width and a few other parameters the machine will default to static balance even if the wheel is spinning on their machine.
          The more I read, the more confused I am between the 3 adjectives for what I am trying to describe when I brake after one 20 minute session.
          I.e. Avoiding Brake Judder at the Track

          Using the following definition and also testing this out on 2 different sets wheels and tires, I want to say it is "Brake judder." I don't get vibration all the time, only at the track after 1 session when there is heat in the pads.
          Brake judder is the vibration felt through the steering wheel and suspension when the brakes are applied at certain speeds and pressures. It can vary from a barely noticeable vibration to a violent judder – experienced either through the brake pedal or steering wheel.

          If you step on the brakes and the steering wheel shakes from side to side or you feel a vibration or shimmy in your seat then you probably have warped brake rotors that need to be replaced or "trued" which is machining the surface of the brake rotor to make it smooth and even again


          Regarding the tire monkey, I am that monkey. I set mine to ALS and the other tire settings are correct. The tire/whee combo that I used last time at most required 0.75 oz. Most of them only required about 0.50 oz.
          How can I do?

          Comment


          • #6
            Cracks rotors also possible, check both sides. Pad deposits on rotors also possible. Do you get a thump thump when rolling around the paddock while dragging your brakes a little?

            Comment


            • #7
              Originally posted by ebruner View Post
              I've had this issue pop up due to 3 separate issues on my miata. Once it was because I was giving vendor rides at MRLS and was doing 3 hot laps and coming back into the pits to strap the next rider in. The lack of cool down laps and having to touch the brakes in the pits occasionally cause my rotors to warp. That, is likely not your issue.

              The other time this has happened is when I've had a wheel bearing/hub start with one foot in the grave. I've found that of the 3 front wheel bearing failures I've had, 2 of them would start to show signs of imminent death by getting thumpy when they got very hot. Basically towards the end of the session they would get hot and felt almost like a warped rotor.

              The last issue, which I feel may be your issue, was that when I was running a very aging set of carbotech's (XP10) and they would get down in material... they would get thumpy. I am not 100% sure this is a thing and I would speak to emilio about this. However I was experiencing what you describe and mentioning it at lunch to other miata people (eric and brett) and they mentioned that carbotechs can get thumpy when they are very low on material.

              Not 100% relate-able to your situation obviously because of a different car, but I just thought i'd mention a few possibilities to get the juices flowing.
              My wheel bearings are only about a year or 2 old, but I have probably put 20-30 track days on them and I do run a 20mm spacer to clear my suspension. Thanks for getting the juices flowing. I'll have to take a closer look at my wheel bearings.

              Originally posted by ucfbrett View Post
              Since Eric and I spoke about thumpy brake pads, I've have had what alcoholics refer to as a moment of clarity. I had been tossing my Carbotechs before they were worn past the center groove, but through random instances of timing and maintenance, I now think the main culprit was my front hubs.

              In the past, I had experienced vibration up front during braking and thought it was the worn pads and possibly runout in the rotors. It usually happened at the end of the season when I would service the bearings anyway, so I just figured it was the pads. The last race of last season, I discovered it's probably the bearings.

              In addition to what Carl said, check your bearings.
              What is thumpy? By the way, my setup was doing this on new rotors and pads. Pads still have like 80% life (these seems to wear down very slow, which is nice).
              How can I do?

              Comment


              • #8
                Originally posted by robburgoon View Post
                Cracks rotors also possible, check both sides. Pad deposits on rotors also possible. Do you get a thump thump when rolling around the paddock while dragging your brakes a little?
                If I am understanding this correctly, I hear zero "thump" while driving normally. Definitely not a cracked rotor, I've had them before on my S2000.
                How can I do?

                Comment


                • #9
                  Thumpy is the hip new slang for vibration under braking. It could vary from a shaking steering wheel to the sensation of thumping through the wheel. All the cool kids are saying it.
                  www.TrackHQ.com

                  Comment


                  • #10
                    Originally posted by ucfbrett View Post
                    Thumpy is the hip new slang for vibration under braking. It could vary from a shaking steering wheel to the sensation of thumping through the wheel. All the cool kids are saying it.
                    Thank you for that. hahaha
                    How can I do?

                    Comment


                    • #11
                      Probably uneven pad deposits on the rotor, which happens with crappy pads that aren't broken in correctly, aren't let to cool down enough after a session, etc...

                      Never heard of those pads. I'd try PFCs or Pagids.


                      0.02

                      Comment


                      • #12
                        Originally posted by Stuntman View Post
                        Probably uneven pad deposits on the rotor, which happens with crappy pads that aren't broken in correctly, aren't let to cool down enough after a session, etc...

                        Never heard of those pads. I'd try PFCs or Pagids.


                        0.02
                        Decided to try Winmax, but obviously it doesn't agree with my M3... I've been meaning to try out some PFCs, I guess I'll give them a try soon. Thanks!
                        How can I do?

                        Comment


                        • #13
                          PFC's are not easy to bed-in properly too, at least they were not for for me. Once they are all set they work and doesnt wear much, especially with me behind the wheel I have PFC06/08 mix (due to the availability at the time) and it took me a few days to get rid of the shudder/vibration under braking. It has been 2 years since and I have forgotten to worry about the brakes at all.

                          Comment


                          • #14
                            PFC's are really easy to bed in (on new rotors). They DO NOT like to be put on used rotors with pad material from a different company. Use new rotors, bedding them in is quick and easy, and they're awesome.

                            Comment


                            • #15
                              Assuming my issue is an issue with bedding. Am I screwed now? I have 2 track days on them. Winmax W6 bedded in new Brembo blanks.
                              Last edited by BANKAI; 01-19-2016, 01:43 PM.
                              How can I do?

                              Comment

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