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  • Transmission / Overdrive: Overdrive Problems

    I have a 1955 E7 truck with a T86 gearbox with overdrive that I am having a lot of trouble with. I have done all of the tests on engaging overdrive and electrically, it checks out. Driving at speed, sometimes the overdrive works but usually after about 20 minutes, I can't get it to work. When it doesn't work it still checks out electrically and I have no engine breaking at any speed. I have rigged up a 6V feed straight to the solenoid via a switch and that still won't engage the overdrive. When it works it is great, but I'm wondering if it has something to do with the temperature of the oil (GL1). The kickdown also does not work, although I'm less concerned with this. The kickdown tests all check out. I have removed the solenoid, took the cover off, points are clean and it all appears to be working. I have about a 1/2" of play when the solenoid screws are backed off and I pull the solenoid out. The solenoid engages with the quarter turn. Any ideas? Thanks, Nick

  • #2
    1. The oil temperature is not an issue, Nick. If you are running GL-1 90-weight, you are good to go on that.

    2. Have you bench-tested the solenoid? That is, have you tried energizing it on the workbench? (Be careful if you do; they have quite a kick and are best tested when secured in a large vise.) BP
    We've got to quit saying, "How stupid can you be?" Too many people are taking it as a challenge.

    Ayn Rand:
    "You can avoid reality, but you cannot avoid the consequences of avoiding reality."

    G. K. Chesterton: This triangle of truisms, of father, mother, and child, cannot be destroyed; it can only destroy those civilizations which disregard it.

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    • #3
      Yes I bench tested it. It moves very forcefully and the secondary circuit shows voltage when its energized (and not before)

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      • #4
        OK an update. The overdrive functions well for the first 10 mins and then not at all. Let it cool down and I get another 10 mins of overdrive and then nothing. It seems to be heat related. I plan to remove all wires going to the solenoid except the temporary 6 volt feed and try that. If it still quits then it seems its either the solenoid or an internal overdrive issue??? I still have no kick down function - could this be a related problem?

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        • #5
          Originally posted by ncalder View Post
          OK an update. The overdrive functions well for the first 10 mins and then not at all. Let it cool down and I get another 10 mins of overdrive and then nothing. It seems to be heat related. I plan to remove all wires going to the solenoid except the temporary 6 volt feed and try that. If it still quits then it seems its either the solenoid or an internal overdrive issue??? I still have no kick down function - could this be a related problem?
          Just a guess, but I'd put my money on the solenoid.

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          • #6
            How 'bout the governor? Could it be losing its ability to keep the circuit grounded and the solenoid engaged? I am certainly no expert, but don't the transmission have a governor that is required to complete the circuit so that the overdrive solenoid will engage at about 25 to 30 mph?
            John Clary
            Greer, SC

            SDC member since 1975

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            • #7
              The number one cause of overdrive electrical problems in a system that has not been modified/FUBAR'd is the governor. The points get oil fouled when the internal seal fails.

              Instead of wiring a switch to put 6 volts on the solenoid, you should wire a switch from the governor to ground, and make all the rest of the wiring as original.

              There is a set of contacts inside the solenoid that cut the current to the solenoid from a high "pull in" current to a smaller "holding" current. It's possible that those contacts are not working properly causing the solenoid to overheat, but that is not as likely as a bad governor.

              You cannot get the kickdown to work if the kickdown circuit is not working properly - all four wires.

              The shop manual has a nice picture of how the whole system is wired. That same picture has been reprinted in some Motor's manuals and maybe Chilton's as well.
              Last edited by RadioRoy; 03-03-2013, 02:09 PM.
              RadioRoy, specializing in AM/FM conversions with auxiliary inputs for iPod/satellite/CD player. In the old car radio business since 1985.

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              • #8
                Thanks for all the ideas. I tried a switch grounding the governor wire first before I tried other things and it made no difference - but I'm going to try it again. I drove the truck twice today and each time it quit at the ten minute point. The direct feed to the solenoid did nothing - clicked but wouldn't engage. The regularity of how long it'll work for is really puzzeling. I see that there are different length solenoids for different applications. Fifth Ave Garage (wrote the book on R10 and R11 overdrives) sell one at 1" which they claim is the usual length and Studebaker on line sells one that's 1.12" I haven't measured my one but I'm not even sure which vehicle my transmission is from. It has T86 1A any ideas on the correct length?

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                • #9
                  It may be that you are using six volts on a 12 volt solenoid. Also, unsure about a 1" or a 1.12" solenoid. Only solenoid I cam familiar with is about 4" long, and looks like a fat soda can. I still am putting my money on the solenoid, or something related, i.e. six & twelve volt mismatch.

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                  • #10
                    One more thing to check. How about the relay? I have had mine to fail. (As with many of my troubles...years ago) The fuse was OK, so I popped the cover off the relay and found corrosion on the relay points. I cleaned them with a little file I have that is purposefully made for ignition points. If you have a small amount of corrosion on those points, it could explain how they work for a while when cold and perhaps not when they heat up with the engine heat under the hood after the engine warms up.

                    It is not unusual for electrical components to change their conductive value or capability when heat and corrosion are involved.
                    John Clary
                    Greer, SC

                    SDC member since 1975

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                    • #11
                      I'd suspect the solenoid. Get a known good solenoid and try it.
                      the reproductions are problematic in both 6 and 12v versions. Try to find an original.

                      Originally posted by ncalder View Post
                      I have a 1955 E7 truck with a T86 gearbox with overdrive that I am having a lot of trouble with. I have done all of the tests on engaging overdrive and electrically, it checks out. Driving at speed, sometimes the overdrive works but usually after about 20 minutes, I can't get it to work. When it doesn't work it still checks out electrically and I have no engine breaking at any speed. I have rigged up a 6V feed straight to the solenoid via a switch and that still won't engage the overdrive. When it works it is great, but I'm wondering if it has something to do with the temperature of the oil (GL1). The kickdown also does not work, although I'm less concerned with this. The kickdown tests all check out. I have removed the solenoid, took the cover off, points are clean and it all appears to be working. I have about a 1/2" of play when the solenoid screws are backed off and I pull the solenoid out. The solenoid engages with the quarter turn. Any ideas? Thanks, Nick

                      Russ Shop Foreman \"Rusty Nut Garage\"
                      53 2R6 289 5SpdOD (driver)
                      57 SH (project)
                      60 Lark VIII 2dr sd (driver)

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                      • #12
                        Thanks for the help - next step is to replace the solenoid and test that

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                        • #13
                          I'd start by cleaning ALL the contacts.... and checking and cleaning ALL wiring connections.... This includes the contacts inside the Soleniod and Governor....
                          a loose Hi-resistance connection can cause all kinds of havoc.

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                          • #14
                            I have not cleaned all the internal contacts yet - its a good idea - I'll try that - thanks

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                            • #15
                              what Mrs. Corbin said.....90% of my electrical problems are contacts/connections...

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