Overdrive ? Tell me I don't have a problem

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Paul Bennett

Well-known member
BACKSTORY - I am not familiar with the operation of my overdrive, so with my steering fixed, I am finally driving short town distances rather than just around the block.

My speedometer stays at zero when starting to move in low gear, then pops up, overshoots, then settles at roughly at 20mph. Since I'm accelerating and/or shifting into 2nd, have one eye on the OD bulb (below), the actual mph and this aspect of my situation is likely completely meaningless. But maybe not.

BEGIN - I wired a bulb to the overdrive relay indicating juice to the solenoid. I placed it on the floor visible to me while driving. It comes on at about 15 or 20mph, below the 26 mph workshop manual figure. Dropout seems to be almost the same point whereas 23mph is the workshop manual number. Since I am usually accelerating in low or already in 2nd gear, when I lighten up the gas pedal (such as during the shift to 2nd, the overdrive becomes noticeably active when I'm back on the gas. In any case the OD definitely engages.

In the case of heavy traffic town driving, the solenoid will be on/off quite often which can't be good. But then I'm not familiar with this OD and this my be a total non-issue.

Questions:

  1. Should I send the OD velocity module for rebuild to place it in spec? (if yes, who rebuilds)
  2. Given the speedometer abnormality perhaps I'm being influenced by faulty speedo numbers and the real OD activation is fine. Agree? After all, 23 and 26 aren't that much apart. So,
  3. Is this a non-critical situation and just ignore it?
  4. In the next ? months I plan to replace this engine in which case the OD will be out of the car. Should what be send to who for rebuilding.
OBSERVATION - Gearing with my town driving so far is different as 2nd feels like 3rd. My kickdown switch isn't adjusted properly (too low to floor) so I haven't been able to test that function also I don't detect the free-wheeling that I've read about. My engine while idling fine, runs like crap and overheats within ten minutes so I haven't been on the highway. But all in all, this tall 2nd gear town driving seems ok.
 
The overdrive governor is independent of the speedometer so one does not affect the other. One way to check if the unit freewheels below the nominal 27 MPH engagement speed would be to run up to 20 MPH or so and turn off the ignition with the car in gear and the lockout knob pushed in. The engine should stop while the car keeps coasting.

Your speedometer may just need the cable cleaned and lubed. Remove the cable housing from the back of the speedometer and pull out the cable. Wipe it down with a rag soaked with carb cleaner, lacquer thinner, etc. Go to an old time parts store with an old time parts man. Get what he recommends for speedometer lube and lube the cable as you slide it back into the housing. Put a drop of oil on the shaft that the speedometer cable fits into.

Don't worry about the O/D relay cycling the solenoid on and off. It's the way they are made.
 
As 40Delux states, the speedometer and the governor are not dependent on each other’s operation to function correctly. The only common factor is that they both are driven off the same gear in the transmission. The erratic action of your speedometer is probably due to a dry cable, a failing cable, a worn speedo driven gear, or a failure speedometer (the dash gauge). The cable and gear are easy to check and repair. The dash unit would require a bit more knowledge and experience to rebuild.

It sounds like the overdrive is functioning correctly. You can check the freewheeling aspect by doing the test he described. Once the transmission has shifted into overdrive, you wouldn’t feel any freewheeling.....you would have engine braking as long as it’s actively engaged in overdrive (and you’re over approximately 28 mph). Even though you have the cable control handle pushed in (this enables OD) the governor and solenoid will pop it into OD as determined by the vehicle speed.
 
All above are correct. Drive with a GPS and use that speed. If you don't have one you must have a friend who does. Those governors are pretty solid and other than cleaning the points are pretty reliable. If you are doubtful about it you can disassemble it and run up the speed with a drill motor to observe the operation.
 
When you are driving in OD and can't kick it down with the kick down switch in the floor, just cut the ignition switch off and back on as fast as you can and it will shift out of OD and when you let up on the gas pedal, it will lock back in. I do this all the time when I want to shift it out without flooring the gas pedal.
 
Thanks for all the good help and insight for my understanding this new (to me) component.

I never meant there was a link between the speedometer problem and the overdrive function. I brought it up as it makes it difficult to establish that magic engagement speed when the speedo is a distraction at/near the speed point I'm interested in.

My next overdrive research will be to learn how the solenoid likes 12v. Saw the rebuilder today who gave me a large enough reason to convert to 12v so that I caved on my 6v stance. Mostly starting a flatty with 9:1 compression.

Agin tks all. And I will clean/oil my speedo cable.
 
I agree with all of the above. Lube speedo cable, and lube the input shaft of the speedometer itself and make sure it's not binding up from old crusty lubricant.

If you have a smartphone, you can download a free speedometer app so your phone can act as a GPS speedometer.

Not sure what you mean by "heavy town traffic driving" but the power to the solenoid will "bobble" only between the two trigger speeds (23 and 26 +/-). If it's bobbling above or below those speeds you have an electrical circuit problem somewhere.

The power to the solenoid should not vary. It's either on or off. If your indicator bulb gets brighter on accel and dimmer on decel, you may have a problem with your battery, generator, or regulator. Generators are very weak at low RPMS in the first place, and they ramp up output voltage at high speeds, unlike alternators which are virtually the same voltage at any speed. Your headlights will also run dim/bright at different RPMs. The regulator is designed to even this out, but it may be failing. You also need to clean and tighten all connectors because 6V systems are sensitive to dirt/cruddy connectors.

Also beware that these solenoids are very sensitive to electrical drops. Anything less than 6V will probably fail to engage OD, and may also cause OD to disengage prematurely. Your dimming bulb may be telling you about an unknown voltage drop.

I have a friend who has been running a 6V solenoid on 12V for over 20 years with no problem.
 
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