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Tachometer problem

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  • Tachometer problem

    The tachometer in the '62 Hawk I have will sometimes read 2200 rpm at 65mph....sometimes it will read 2650 rpm at 65 mph...and today it only felt like registering 1950 rpm at 65 mph. Sometimes all I have to do is shut the motor off and come back in 5 or 10 minutes, take off again, and it will read something entirely different than it was reading previously. The needle is steady and does not jump around or waver.

    What gives with this thing...what could be the cause and what would be the potential remedy?

    Any ideas?

    Karl


    1962 GT Hawk 4sp

  • #2
    More then likely, it's a sticking tach that's dried out of lube.

    64 Commander 2 dr.
    64 Daytona HT
    63 Cruiser
    63 R2 4 speed GT Hawk (Black)
    63 Avanti R1
    63 Daytona convert
    63 Lark 2 door
    63 Lark 2 door #2
    62 Daytona HT/ 4 speed
    62 Lark 2 door
    60 Lark HT
    60 Hawk
    59 3E truck
    52 Starliner
    51 Commander

    JDP Maryland

    Comment


    • #3
      quote:Originally posted by JDP

      More then likely, it's a sticking tach that's dried out of lube.
      Ok, let's run with that idea. What would I need to do (my repair manual still has not shown up, so I have to "hoof" this alone and in the dark), to unstick the tach and what sort of lube should I use in the process?

      Also keep in mind that when cruising at 65 mph, when I push the clutch in and rev the motor up, the tach needle does respond accordingly.....albeit most likely inaccurately. So, it's not like it's simply "stuck" in the sense of being "frozen in position".

      Thanks for your response.

      Karl


      1962 GT Hawk 4sp

      Comment


      • #4
        I sure could use some additional expert advice here on this matter. I just got my service and repair manual and on the subject of the tachometer, all it talks about is the part(s) associated with the distributor.

        It says nothing about the drive cable and the actual "head unit" itself in the dash. Is the irratic action of the tach something which I can address and take care of, or do I simply need a whole new (different) unit?

        I hesitate getting too involved with this thing, not knowing anything about how it functions. Anyone who can offer some 'words of wisdom' would be most appreciated.

        Karl


        1962 GT Hawk 4sp

        Comment


        • #5
          I'm not an expert on Tachometers but had to replace the driver for same on my 63 Hawk. I will be
          watching this thread for any expert advice cause mine hunts a bit. Two things.
          1. be sure you have the meter cover grounded well
          2. If your sender is a small rectangular box--there is a 1/8 " hole in the cover to adjust something.
          I haven't fooled with the adjustment yet myself.
          The 1950 Champion Starlight
          Santa Barbara
          CA

          Comment


          • #6
            Those were electric tachs and didn't use a speedometer type drive cable. I believe the GT tachs are pretty much the same as the 55 Speedster tach except for the voltage. Instead of using a cable turning a magnet to drag the needle along, it uses a synchronous electric motor which is powered by the electrical pulses sent to it by the sender on the distributor. I think first I'd check the brushes on the sending unit. Iv'e never had my hands on one, so I'm just going by how they work. I'd see if the commutator it dirty or possibably oily. I don't know it I'd use brake cleaner to clean things because that's some pretty stout stuff and it doesn't like some plastics. Starting fluid without "upper cylinder lubricant" (light oil) is good for removing oil and it then evaporates away leaving thing high and dry. You might see if the brushes are in firm contact with the commutator. If they aren't, that could give erratic readings. If that doesn't do any good, you might then remove the tach. On the back you should be able to remove two small (5/16"?) nuts and the rear half of the motor shell can be slipped back while you thread it over the cable. You'll find four little brushes located 90 degrees to each other. If you look down between these, you will see the rear bushing the motor shaft rides on. You might take a little WD-40 and lubricate the bushing and see if that helps. Take a look at the commutator surface the brushes ride on and it should look fairly clean and copper colored. If it looks dirty or kind of burned, it will probably need to be cleaned and the brushes might be worn. I haven't torn one apart completely, so at first I'd just try lubing the rear bushing. If that doesn't help, I have a Speedster tach in the shed I can try to pull apart to give you better instructions on going further. Oh, you might make sure the electrical connections of the three prong plug are clean and any other connections on the sender. To me it sounds like either the tach motor shaft needs lubing or it's getting erratic signals delivered to it. Everything I've described so far is pretty simple and just about anyone could do it, so don't fret about it.

            Comment


            • #7
              The GT tachs are early electric tachs and aren't all that accurate. The technology has improved a lot since then. I agree with Starlight, make sure there is a wire running directly from the case of the dial to a good ground like the brace at the bottom of the dash. This ground will solve a lot of tach problems.

              Tim K.
              '64 R2 GT Hawk
              Tim K.
              \'64 R2 GT Hawk

              Comment


              • #8
                quote:To me it sounds like either the tach motor shaft needs lubing or it's getting erratic signals delivered to it. Everything I've described so far is pretty simple and just about anyone could do it, so don't fret about it.

                Oh but I do fret over such things, John. I feel like a person who is comfortable filleting a fish, being asked to perform open heart surgery.

                Your explanation is very concise sounding....but me and my dummie mentality here, is not certain if all you are referring to is contained within what I would call the tachometer head (the gauge on the inst panel), or the components that drive the thing found inside the distributor.

                Indulge me please, and walk me through this one more time, if you would. The manual states explicitly not to be lubing anything to do with the tach sending unit, so that further adds to my confusion here.

                Anyway, if push ends up becoming shove and I need to focus my attention on the dash unit.....do I need to actually remove the unit from the instr panel? According to the instructions, that sounds like a real PITA job, taking the panel apart.

                I know I could probably take the easy way out and buy an aftermarket Sun tach, but I'd really rather keep the stock one if at all possible.


                1962 GT Hawk 4sp

                Comment


                • #9
                  quote:Originally posted by GTtim

                  The GT tachs are early electric tachs and aren't all that accurate. The technology has improved a lot since then. I agree with Starlight, make sure there is a wire running directly from the case of the dial to a good ground like the brace at the bottom of the dash. This ground will solve a lot of tach problems.

                  Tim K.
                  '64 R2 GT Hawk
                  I kinda gathered that, from reading the manual, Tim, but it doesn't ease my mind when it comes to messing with it. However, I definitely can check to insure it is grounded properly and that the rest of the wiring is in order.

                  This Hawk is in fine condition overall...just a few little things that need to be brought up to snuff that's giving me fits.

                  Thanks for the response and tips.


                  1962 GT Hawk 4sp

                  Comment


                  • #10
                    If you think getting it out of the dash is a PITA, wait until you remove the bezel to check the movemaent. It might be better to risk the $80 on a new sender first.

                    64 Commander 2 dr.
                    64 Daytona HT
                    63 Cruiser
                    63 R2 4 speed GT Hawk (Black)
                    63 Avanti R1
                    63 Daytona convert
                    63 Lark 2 door
                    63 Lark 2 door #2
                    62 Daytona HT/ 4 speed
                    62 Lark 2 door
                    60 Lark HT
                    60 Hawk
                    59 3E truck
                    52 Starliner
                    51 Commander

                    JDP Maryland

                    Comment


                    • #11
                      I would agree with JP on this one. If you think it is difficult taking the tach out try fixing it once you get it out. You have to pry up the black retaining ring ever so carefully, clean everything (glass, dial face)lubicate, reassemble then hit the retaining ring back down again. Just when you think you have it back together..... you have to get it back into the chrome face ring only to discover it does not fit anymore! Try to do that with your newly purchased $250 USD Rare Redline Tach! Good luck if all else fails I have a perfectly working standard tach that I replaced with my redline tach that is sitting on my shelf.- Allen



                      1964 GT Hawk soon to be R2 Clone
                      1964 GT Hawk
                      PSMCDR 2014
                      Best time: 14.473 sec. 96.57 MPH quarter mile
                      PSMCDR 2013
                      Best time: 14.654 sec. 94.53 MPH quarter

                      Victoria, Canada

                      Comment


                      • #12
                        Hi Majik (Puff?)
                        Look at the post today on Clock/Tach and go to the address suggested by B. Shaw.
                        This will give you everything you need to know about how the tach works and how to trouble shoot. It is an EXCELLENT treatise albeit quite technical. Basically it shows how the points
                        opening and closing create a pulse rate that the sender uses to average out a current that energizes the magnetic coil and hence the ponter. It explains how to check out the Tach. head and the sender unit in great detail.
                        BTW did you check the case ground and adjust the rheostat through the hole in the sender unit ? Did it help ?

                        1950 Champion Starlight
                        1963 Hawk GT
                        Santa Barbara
                        CA

                        The 1950 Champion Starlight
                        Santa Barbara
                        CA

                        Comment


                        • #13
                          quote:
                          .............or the components that drive the thing found inside the distributor.
                          No tachometer components inside the distributor, that was a different system used on 1961 and earlier.


                          Dwain G.

                          Comment


                          • #14
                            The manual says not to lube the sending unit on the distributor because any oil that gets between the brushes (the square or rectangular graphite things that ride on the commutator) and the commutator (the segmented part of the shaft they ride on)will cause a bad connection. Something like some points cleaner or starting fluid would clean off any carbon dust without leaving an oily residue. I believe that's the first thing I'd do. While you're at it, take something like a toothpick or sharpened pencil (not sure of how much room to work) and slip the point between the commutator and the brush (don't worry, you won't hurt anything) and push the brush away from the commutator. The brush is spring loaded and should provide resistance from the get go. If the brush seems to lack firm pressure against the commutator, it is probably worn. Most brushes I've seen regardless of the application tend to be around twice as long as they are wide. When they get "square", the spring pressure is usually too little to make good connection. Like I said, I've never had my grimy mitts on a sending unit, but I'd expect the brush to have a braided copper wire attached to it coming out the side or end of the brush holder. The little coil spring behind it is most likely not restrained in any way. So if you remove the whole unit or take things apart, be careful that the spring doesn't jump out. If the brush seems too short and/or the spring pressure too little, you might be able to fashion a little spacer to place behind the spring opposite of the brush end. Whittle a little piece of wood, cardboard or the like about the thickness of the brush and that should increase the contact pressure of the brush. If things work better, then you know the brushes are worn but it'll probably run a long time that way. If you take the sending unit apart and have unfettered access to the commutator, then is the time to take some 400-600 sandpaper and clean it up if it looks dirty like an old penny that's been exposed to the weather. If it has the color of a penny you carry around in your pocket, don't worry.

                            Removing the tach in a 60 Hawk is a pain and I'm sure it is in a GT also. A couple of people mentioned possible grounding problems. You might get a piece of wire and affix a little alligator clamp to each end. One you can attach to the little nut on the back of the tach and the other to anything well grounded. That would be a good way to rule that out without going to all the hassle of removing it. I'd probably focus first on the ground and then the sending unit since it's exposed to heat, oil fumes and other elements. If things still act up, then it might be time to check out the tach itself. As I said earlier, I'd look at lubricating the rear bearing on the tach motor. It's easy to get to and my experience with all sorts of electric motors seems that more often than not it's the brush end bearing that's the driest. Id try something like WD-40 first to cut any dried grease and maybe then add just a drop or so of oil. I'll have to look closer at my tach to see how it comes apart when going further.

                            Hopefully it wouldn't be necessary to remove the bezel because I agree, it is a pain. If worse comes to worse and you do, try taking a nail with a head that's a little wider than the distance between the tach case and the lip of the bezel and file one side of the head down to kind of a sharp edge. Bending the nail may give you a better handhold. With this you should be able to use the sharp edge to get under the backside of the bezel and pry up just a bit. Move over and repeat and go around and around like you were opening up a can can of paint. Pry the edge up just far enough to slip it off over the front. For putting it back on, put th ebezel in place and place the tach face down on something solid like a table with a wash cloth (prevent scratching) and push down firmly, applying pressure to the bezel on the bottom. Take a piece of wooden dowl or your wife's wooden cook spoon and bend back a little spot, not all the way but j

                            Comment


                            • #15
                              Wrong year Hawk John, the 62 Hawk is all electronic with a solid state sender.

                              64 Commander 2 dr.
                              64 GT Hawk R2 clone
                              64 Daytona HT
                              63 Cruiser
                              63 R2 4 speed GT Hawk (Black)
                              63 Avanti R1
                              63 Daytona convert
                              63 Lark 2 door
                              63 Lark 2 door #2
                              62 Daytona HT/ 4 speed
                              62 Lark 2 door
                              60 Lark HT
                              60 Hawk
                              59 3E truck
                              52 Starliner
                              51 Commander

                              JDP Maryland

                              Comment

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