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I bought a 1947 Custom Super Clipper late last year and only managed a few short low speed trips before the winter storage season. Overdrive was disengaged for all of them and has been since I bought it and I'd now like to do some highway driving and exercise the overdrive unit. The instructions for use from the previous owner were confusing and unclear so I am hesitant to just do a trial an error run to figure out how to properly engage, use and disengage overdrive.

I've looked through much of the literature in the archives here but didn't come across any driver/user instructions - mostly service information. Can anyone help with some clear how to's, do's & dont's etc? I recall warnings about engaging or disengaging while in motion and cautions about only using it above a certain speed but I'm not clear about the real rules governing use. Thanks in advance for any insights and assistance.

If you car is stock, it will have the R9 overdrive and here are instructions for the operation as taken from the 47 owners manual.




If your car is one which an owner might have paid to have the OD changed to the newer R11 overdrive because of the Reverse gear lockup issue detailed in Service Counselor Vol 21 #15, the operation is almost the same but on the R11 the indicator light mentioned in the R9 instructions is no longer functional. On that OD you need to depend on your senses to estimate the speed and time when OD will become available. Here are the instructions for the R11.




If you are unsure which OD you have, look for the OD relay on the firewall area in front of the driver. The R9 will have a large squarish black box with 6 terminals. It is about the size of a voltage regulator and located roughly below the coil and slightly below and more toward the engine than the voltage regulator. The R11 will have a smaller rectangular shape relay most often in a natural zinc color but some have been seen painted. That relay has 4 terminals, two on each end with a fuse mounted on the forward facing long side.

Thank you Howard - much appreciated. I have the stock R9 unit. The instructions about controlling the on and off state of overdrive while driving is clear. However, just so I am clear about moving the lockout knob in or out, it looks like any movement of that knob should only be done while the car is in motion and above the noted engagement speed of overdrive. Is that correct?

You are correct in that the car should be moving when you decide to lock it out of OD but you can do it at any speed below 60..

The R9 instructions do not mention flooring the accelerator like the R11 instructions do but do mention depressing the clutch. While it is a quite different unit mechanically, it is still a good idea to press the accelerator anyway if you are going above the OD engage speed of about 22 mph just in case OD has engaged.

Doing the accelerator bit ensures that the kickdown switch will kill power to the solenoid while it also causes the engine to miss a beat or two so torque is relaxed for the moment the solenoid needs to retract and forcibly disengage the pawl from the sun gear. Depressing the clutch in the R9 would do about the same thing in reducing torque but would not ensure the solenoid disengages the pawl if car is in OD. Once the pawl is out of mesh the car will be able to drop out of OD. Mechanically disengaging the pawl also clears an internal block in the path so the lockout lever can move gears or rings needed to lock the OD parts together so they can rotate as a single unit.

OK, I think I understand the steps I need to take to initialize OD, use while in motion and disengage OD. As my car currently has the lockout knob pulled out (OD disengaged) I should do the following:

1) Start and drive normally until above the lower limit OD speed.

2) Once at or above the lower limit OD speed push the lockout knob forward to engage OD (green signal light should come on on the speedometer)

3) To engage OD while driving above the lower OD speed limit, momentarily release pressure on the accelerator and OD will engage when accelerator pressure is resumed

4) To temporarily disengage OD while driving, press accelerator to the floor to cut off power to the solenoid and depress clutch to reduce torque.

5) To fully disengage OD pull the lockout knob out while driving below 60 mph.

Last remaining questions are can I leave the lockout knob pushed in (OD engaged) when I park my car and if I do that will OD automatically be available for use on the next drive after I get above the lower OD speed limit? I assume there is no harm in leaving the OD engaged while doing stop and go city driving.

I've never driven a car with an R9 but on the R11, I seem to recall lots of free-wheeling so no engine deceleration, requiring more use of brakes. You'll probably find you have better overall control if you shut it off during around-town driving where it isn't needed anyway.

Lets clarify:

You may push the knob in to make the overdrive available at any time. Before you leave the garage. Driving down the street. Whenever it suddenly occurs to you.

Anytime the green light comes on and it seems appropriate from 20 mph to 90 mph lift your foot off the gas and the trans will shift up.

Tromp it to the floor any time you wish for passing or hill climbing or embarrassing that clown in the 47 Caddy and it will shift down. Don't touch the freaking clutch.

If you are driving in the mountains and decide you don't want overdrive then merely do what the book says and push in the clutch and pull out the knob while the car is rolling below 60. The instant you move the knob the electrical circuit to the unit will be broken and there is no need to floor the gas. Think about it: if you floor the gas while holding down the clutch in any car you'd better have a magnet to pick up all the engine pieces.

When the knob is in the overdrive is always ready--tomorrow or next week. There is little need to mess with it.

The question remains if your unit works at all as the car is new to you. If when trying it out the car always seems to freewheel--it is not working. That is another issue to tackle.

Thanks for the clarification Ross. Your description and direction makes much more sense than my original interpretation. I'm hoping to get out for a test run in the next week or so and with some luck will find the OD unit is operable (and the driver is still capable of learning something new).