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A-Type Overdrive Solenoid Heats Up and Stops Working

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  • A-Type Overdrive Solenoid Heats Up and Stops Working

    Ok, so it may be that the pull-in coil is kept engaged or the solenoid is faulty but... I've bench tested the solenoid and tested the solenoid installed, and in both cases I am able to see the Ohms change from ~0.7 to ~12.6 (so I believe solenoid works and the lever is properly adjusted.) I followed the test procedure from Moss linked below.

    However, that video is quirky bc at the 4:17 mark, it skips over how to test when the solenoid is energized - that I don't know how to do.

    More info - oil is at the appropriate level, the overdrive functions properly when I manually engage it, the solenoid works fine when I first start driving but eventually heats up and seems to not be strong enough to pull the lever (I can see it start to pull but doesn't go all the way up - I am able to push it up and then it engages.). Also, I did burn out the prior solenoid - I think the lever at the time was not properly adjusted but it's also possible I still have the same problem.

    Thanks in advance!!!

  • #2
    One way to test the solenoid while it is energized would be to connect an ammeter in series. The problem with that is most multi-meters with ammeter functions are limited to 10 Amps and if you're reading .7 Amps on both solenoid coils, that would draw 17.14 Amps and would immediately blow the Ammeter.

    If you have an earlier car with an ammeter, I could tell you how to connect the solenoid with a jumper to allow the ammeter to read the current flow to the solenoid. It wouldn't be an exact reading, but you should be able to visualize what's happening.
    R3
    Jim Herter,͏͏͏͏͏͏͏͏͏Copperas Cove, TX
    Original Owner ֍ 1970 TR6 CC 50990 LO

    Comment


    • #3
      Hey R3 - I have a cheaper multimeter so I don’t think I can use it.

      But...my car does have an ammeter! Like yours, my car is also a ‘70. I’m all ears, THX!

      Comment


      • #4
        Power to the solenoid does not normally go through the ammeter. Temporarily jumping the wires as per below will send the current through the ammeter.

        Click image for larger version  Name:	DSC00481.JPG Views:	1 Size:	717.7 KB ID:	542148
        • From the smaller overdrive harness, there should be a brown wire (shown on the left side of the picture) connected to the Aft side of the fusebox.
        • Pull this wire from the fusebox and pull the alternator plug(s) from the alternator (you may have one or two plugs depending on the type of termination).
        • Jump the brown OD wire to the large brown/white wire in the alternator plug.
        • With the ignition switch on and gearbox in 2nd, 3rd, or 4th, toggle the OD switch on and off.
        Caution: Be careful that the jumper from the alternator plug does not accidentally come into contact with ground.

        If the adjustment is good, I think you will see a quick large jump of the ammeter needle to the negative (-D) side, followed by the needle settling down to a slight discharge. Your 12.6Ω reading should be less than 1 Amp. As you turn the OD switch back off, the discharge rate should drop a bit lower, or at least you should see the needle flicker for a moment.

        If the adjustment is not correct and the pull-in coil never drops out, you should see a great rate of discharge, maybe up to half of the discharge scale.

        Let me know how this works.
        Last edited by RatRidgeRoadster; 06-12-2021, 11:50 AM.
        R3
        Jim Herter,͏͏͏͏͏͏͏͏͏Copperas Cove, TX
        Original Owner ֍ 1970 TR6 CC 50990 LO

        Comment


        • #5
          Ok so two pieces of good news and one bad news

          First, thx for the inspiration to reconnect my ammeter! I had bypassed it when I did the Bosch alternator upgrade (two decades ago...sheepish grin). I had bought a voltmeter to install and then read about installing a shunt in the ammeter...so I did neither. Until this morning. I didn’t have 16 ga wire so I used 14 ga (thinking a thicker wire would be safer anyway- not to hijack my own thread but pls tell me if I’m off.) So, I now have a functional ammeter!!!

          Second piece of good news - my solenoid does seem to drop to the holding coil. I’ve attached a video (hopefully it works 🤞). I did it in slow motion just to make sure (first part is in regular speed and the second time I test is in slow-mo. The noise in the background is my electric fuel pump).



          So I guess the bad news is I still haven’t figured out why the solenoid gets hot and stops working. Frustratingly, it takes about 15-20 min of driving bf this happens so replicating the problem takes time.

          Did I do the test wrong? Any other thoughts on what else to check? THX!!!


          Comment


          • #6
            I was expecting a bit more of a spike when you first energize the solenoid, but I guess with the almost instantaneous engagement the ammeter just can't respond fast enough. What appears to be the hold-in current seems to be about right.

            Did you use the 3/16" drill bit to set the adjustment?
            R3
            Jim Herter,͏͏͏͏͏͏͏͏͏Copperas Cove, TX
            Original Owner ֍ 1970 TR6 CC 50990 LO

            Comment


            • #7
              I did use a 3/16” bit to check how close it was but I also read conflicting reports on how accurate it was over time (tho my overdrive was rebuilt within the last 15k). Having said all that, I’ve been driving it without the tunnel cover on and manually pushed the lever up while driving. It engages before I reach the end of the solenoid throw and can then keep going to engage the holding solenoid button. THX!

              Comment


              • #8
                How is the solenoid grounded? Just to the transmission or chassis or both?
                CF1634U+O Pimento/Chestnut
                2nd owner, since 1975
                Now in Fair Oaks, CA

                Comment


                • #9
                  Hi baws - it’s only grounded to the tranny. I actually took the cork gasket off to make sure it had a better connection. I will check the battery strap - if I recall correctly, it runs to the chassis and then to the engine. Should there also be a strap from the engine to the tranny? THX!

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                  • #10
                    The ground to the engine, also grounds the transmission. The battery's ground strap eyelet is on one of the bolts holding the transmission to the engine
                    Driving a 1973 TR6
                    Doing ZS carb repairs
                    email kencorsaw"at"aol.com

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                    • #11
                      Taking the gasket off might change your adjustment,might not seam to be alot,thin cork gasket

                      Comment


                      • #12
                        Originally posted by Leebo View Post
                        Hi baws - it’s only grounded to the tranny. I actually took the cork gasket off to make sure it had a better connection. I will check the battery strap - if I recall correctly, it runs to the chassis and then to the engine. Should there also be a strap from the engine to the tranny? THX!
                        Reason I asked was, I had issues with my J-Type solenoid intermettinley working until I added a ground directly from it to the engine/body ground point.
                        Also, a separate but equally electrical issue I had with a component/wiring overheating (cooling fan), was cured by improving the ground connection from the relay.
                        CF1634U+O Pimento/Chestnut
                        2nd owner, since 1975
                        Now in Fair Oaks, CA

                        Comment

                        A-Type Overdrive Solenoid Heats Up and Stops Working

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