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  • Clutch Delay Valve

    Hi,

    I need to replace the flexible clutch pipe on my car - clutch drag when hot.

    Just had the under tray off to have a look. I can't see anything which looks like a clutch delay valve (thank heaven). Am I correct?

    Thanks in advance.
    Attached Files

  • #2
    Yes there isn't a cdv as such but the hose itself act as one, if that makes sense,


    http://www.z3mcoupe.com/forum/showthread.php?t=12697

    Comment


    • #3
      Originally posted by Dave P View Post
      Yes there isn't a cdv as such but the hose itself act as one, if that makes sense,


      http://www.z3mcoupe.com/forum/showthread.php?t=12697
      Not really - how does it do that?

      Comment


      • #4
        Originally posted by FEP View Post
        Not really - how does it do that?
        There is a restriction built into the hose.
        Last edited by Dave P; 04-06-2015, 12:51 PM.

        Comment


        • #5
          http://www.zeckhausen.com/cdv.htm

          explained

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          • #6
            Originally posted by MasterMiller View Post
            Excellent. This seems to suggest that no Z3M's had CDV's. That's not what others on this forum have found. Perhaps none in the US had them. BMW must have reckoned that US drivers were more able to handle a clutch that UK drivers!

            Comment


            • #7
              I had my original hose replaced with an earls braided and definitely notice the difference now, especially when changing from 1st to 2nd. Got rid of the 'jerk' and feels normal now.

              Comment


              • #8
                Originally posted by FEP View Post
                Excellent. This seems to suggest that no Z3M's had CDV's. That's not what others on this forum have found. Perhaps none in the US had them. BMW must have reckoned that US drivers were more able to handle a clutch that UK drivers!
                Oh yes they had... or at least my UK spec S54 had. It is a fairly insignificant extra metal section built into the hose at the slave cylinder end. I got fed up with not being able to select gears easily, despite having changed gearbox oil and clutch fluid, so I replaced my hose with one intended for a lesser Z3 which does not have the delay valve. The gear change is greatly improved. When you get the old one off, have a close look at the slave cylinder end. You'll see how it works. It's a relatively easy job as long as you can undo the hose from the pipe in the engine bay. I ended up carefully hacksawing through the union longitudinally.
                My E46 330i also has one, must get round to removing that too.
                Roger

                Comment


                • #9
                  All Z3Ms had the so called CDV. Its not really a valve anyway. It's a restriction in the hose that slows down the fluid and as a result slows clutch engagement.

                  Here is a good thread form Bimmerfest on the subject.

                  FWIW, I have had a braided Earls hose on my S54 for 10 years now. One of the best mods I ever did.

                  Comment


                  • #10
                    Originally posted by siwilson View Post
                    All Z3Ms had the so called CDV. Its not really a valve anyway. It's a restriction in the hose that slows down the fluid and as a result slows clutch engagement.

                    Here is a good thread form Bimmerfest on the subject.

                    FWIW, I have had a braided Earls hose on my S54 for 10 years now. One of the best mods I ever did.
                    Thanks for that.

                    Looks like its Earls for me.

                    Surely it must be more than just a restriction - isn't the idea that it can disengage instantly but engages more slowly?

                    Comment


                    • #11
                      Mentions an internal spring in that piece so guess it's a type of check valve in that it's fully open in one direction and restricted to whatever in the other direction (i.e the engaging direction).
                      Last edited by MasterMiller; 04-06-2015, 09:03 AM.

                      Comment


                      • #12
                        Don't think mine had a CDV, just a smaller hole at one end that I could see. But most of the problems people find with the stock hose is due to the pipe expanding, moreso when hot. If you get someone to press the clutch down whilst you watch the pipe it expands like a balloon.

                        I fitted £9 a brake line to mine!

                        Comment


                        • #13
                          Yes, the brake line's a good option.
                          But it can't be just swelling of the hose as my clutch action was greatly improved by switching to a non-CDV clutch hose, from a smaller-engined Z3. I would assume BMW's clutch hose material is of the same spec for all.

                          ...and, thinking about it, if there's a restriction in the hose (CDV), it would tend to cause the hose to swell under pressure!

                          Comment


                          • #14
                            Originally posted by FEP View Post
                            Thanks for that.

                            Looks like its Earls for me.

                            Surely it must be more than just a restriction - isn't the idea that it can disengage instantly but engages more slowly?
                            Nope, just a restriction. Remember to disengage it's your foot power which can vary. To engage it's just the clutch spring which is constant. I had 2 issues with the stock hose.

                            1. A quick shift could burn the clutch if I gave it the gas before the clutch had fully engaged. Never happened since the new hose.

                            2. The old hose would get hot and go soft in traffic. This caused it to balloon and the clutch not disengage properly. Again, never happens now.

                            Comment


                            • #15
                              Thought that I would post the conclusion - may help others.

                              The old hose did indeed appear to have some kind of additional element at one end - as per the Bimmerfest thread above.

                              Access is from above and below. As there doesn't appear to be any suitable central jacking point at the front, I had to jack up each side in stages until the car was standing fairly high on axle stands under the two wishbone support brackets - I position them so that they sit on the bracket and the bolts evenly. AS GOES WITHOUT SAYING, MAKE SURE THAT THE CAR CANNOT MOVE AND THAT THE STANDS ARE SUFFICIENTLY STRONG/STABLE.

                              The engine undertray comes away after having removed 8 8mm bolts and two 10mm bolts.

                              Getting spanners on the hose joints was not easy - particularly the top one. They both require two spanners to hold the pipe union nut and the pipe end but there isn't much room to get two hands in for the top end. I had to undo the coolant reservoir and some of the hose clips and push it as far back as I could to squeeze in from above. I also removed the rubber hose that connects the air filter box from the inlet plenum - comes away fairly easily having removed the two big jubilee clips.

                              The replacement Earls hose has female unions on both end, but came supplied with a female to male adapter, which screws directly into the slave cylinder, not forgetting the brass sealing washer that came with the hose.

                              The bracket that supports the lower end of the original hose is fixed with one of the slave cylinder supporting bolts. I left it in place but pushed it back towards the bell housing as far as I could. A short length of pipe from the hose to the slave as well as a little union holder piece are now redundant.

                              It is then pretty straightforward to attach the hose to the adapter already screwed into the slave cylinder and to the pipe from the master cylinder at the top end. The hose has a longish ferrule at the top end which slides through the rubber bush in the union support, though in reality that support isn't doing much - the hose is only attached firmly to the pipe.

                              Then came bleeding of the clutch. I used my trusty Gunsons 'Easybleed' attached to the front tyre having dropped the pressure to 20psi. I didn't even need to put DOT 4 in the easy bleed reservoir - just topped up the clutch/brake reservoir and by the time the bubbles had come out of the bleed nipple on the slave (via a push on clear hose into a jar), the level in the reservoir had hardly dropped.

                              Result is not startlingly different from before, except that the clutch bite point is the same cold as it is when everything is up to heat.

                              Hope this helps someone.

                              Rupert

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