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Overdrive Function: Hopefully make a sticky thread from this. EDIT: I added new information. (9/13)

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  • sactorandy
    replied
    Perhaps a brief discription of the external OD parts and their operation would be helpful. IE: solenoid, speed governer, relay, reverse lock-out switch, and throttle kick-down switch. This has been a learning curve for me over the last 2 years on my 55 Champion. I bi-passed everything and connected the solenoid directly to a toggle switch and now the world is good again. Thanks for trying to clarify this mystery for those of us that know just enough to get into trouble.

    Randy

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  • StudeRich
    replied

    As Bob P mentioned the clutch does not need depressing.
    But, I am saying that you do not "PULL" the O.D. Knob, you PUSH it in.

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  • StudeRich
    replied
    Originally posted by 9echo View Post
    The O/D is engaged by letting up on the accelerator when the speed is above 28 to 32 MPH. Of course, the O/D button must be pushed in to allow the engagement. The O/D will automatically drop out when the speed drops below about 28 MPH.
    I think the word Tom is looking for is "GOVERNOR" this is controlled by the Governor, and yes centrifugal force on counterweights is used.

    But really, the way I understand the intent of this string was to explain it's use, not HOW it works.

    Leave a comment:


  • 9echo
    replied
    The O/D is engaged by letting up on the accelerator when the speed is above 28 to 32 MPH. Of course, the O/D button must be pushed in to allow the engagement. The O/D will automatically drop out when the speed drops below about 28 MPH.
    Last edited by 9echo; 09-09-2013, 02:12 PM.

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  • wittsend
    replied
    As an "OD" novice reading this I do not think I understand the part about the cut-in speed. This is what I think it does. - Even if the OD is available (armed, but not active) it will not engage until a certain speed is reached. Is that correct? And if that is correct, what method is used to create the engagement (centrifugal weights???)?

    Also, it seems if the accelerator is push abruptly ("flooring it") the OD will release. What causes the release? (It seems that would throws my centrifugal weight guess out the door.)

    Tom

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  • BobPalma
    replied
    Good idea! Corrections / Notes in RED:


    Originally posted by '66Commander View Post

    Before I explain what Overdrive is, let me explain a few terms:
    When explaining the amount of gears [should be the number of gears. Grammatically, amount is a quantity, like a quart of milk. Number is something you can count; i.e., number of gears]So what is Overdrive?
    Overdrive changes the gear ration [I think you mean ratio] from the input shaft in the gear box. It changes the ratio to reduce the engine RPMs by 30%; thus effectively reducing the engine noise and vibration to half. [wouldn't it be "by 30%," rather than "to half?"]

    What is the goal of Overdrive?
    The goal of overdrive is to reduce [engine] RPMs. This will lower engine wear, produce better gas [mileage], however this will limit your top speed. How this is possible is that it takes 12 horse power (HP) to drive a car at 40MPH. However, there must be an additional 18HP to make up for overall power-plant loss. With OD engaged, it reduces the additional HP from 18, to 11. Making the overall HP at 40MPH 23 (OD engaged) v. 30 (OD disengaged.) [I'm not sure I'd include all that, since it varies by drive train.]

    When the car is below Cut-in Speed (CiS) the car is in Direct Drive (DD). For example, when my 3 Speed w/ OD 1966 Commander is in 3rd the gear ratio is 1:1; the Transmission Input shaft and Transmission Output Shaft are turning the same revolutions per minute. But when you are at or above the CiS you can engage OD. This would change your ratio to .7:1, Transmission Input shaft:Transmission Output Shaft.

    How do I make OD available, and engage it?
    To make OD available you must push down the clutch pedal [????], [not really necessary to disengage the clutch; just make sure the car is accelerating and not in overdrive while you accomplish this]to activate the kickdown circuit. This will drop the car back to straight third (no overdrive), raising the RPMs, disengaging

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  • 41 Frank
    replied
    Correction needs to be made. You push in handle to engage OD you pull out handle to disengage OD. Not a good idea to disengage OD by pulling knob out while moving. Might want to clarify this.

    Leave a comment:


  • Overdrive Function: Hopefully make a sticky thread from this. EDIT: I added new information. (9/13)

    Overdrive Function: (This post has the most current information as of 9-13-13)

    Before I explain what Overdrive is, let me explain a few terms:

    So what is Overdrive?
    Overdrive changes the gear ratio from the output shaft in the gear box. It changes the ratio to reduce the engine RPMs by 30%; thus effectively reducing the engine noise and vibration to half.

    What is the goal of Overdrive?
    The goal of overdrive is to reduce engine RPMs. This will reduce engine wear, reduce fuel and oil consumption. However this will limit your top speed.
    With overdrive available, and the car is below Cut-in Speed the car is in Direct Drive (DD). For example, when my 3 Speed w/ OD 1966 Commander is in 3rd the gear ratio is 1:1; the Transmission Input shaft and Transmission Output Shaft are turning the same revolutions per minute. But when you are at or above the Cut-in Speed you can engage OD. This would change your ratio to 0.72:1, Transmission Input shaft:Transmission Output Shaft.

    How do I make OD available, and engage it?When is it appropriate to use OD?
    It is best to use OD when driving on flat ground. Especially on long stretched driving. Like the freeway. You can also leave OD so it is available while you are driving around in the city. Some folks prefer to do that.
    HOWEVER!! If you live in a mountainous area, like myself, it is best to leave it unavailable. Unless you are going onto the freeway of course. If you are using engine braking you want to ensure OD is locked out (knob completely pulled out). When OD is enabled and/or available, the transmission will be freewheeling and you lose your engine braking capabilities. Be careful.
    Also, you do not want to engage OD while in 1st gear. The engine will be unable to handle the torque, and you will be at risk of blowing your engine. Let alone that being in first gear and at the cut-in speed is bad in of its self. It is okay to have OD available, just not engaged.

    How can I use it in city driving?
    Considering that most intercity speed limits are 25 to 35mph you can use 2nd w/ OD as a 3rd gear. This is entirely up to you.
    With most stops within the city some drivers like to start their car in 2nd gear DD. Once they accelerate to cut-in speed, they would engage OD. The gear ratio of 3rd DD is similar 2nd w/ OD in most vehicles. Stopping would consist of the normal, pushing the clutch pedal and using the brakes to stop. And if you needed the torque of 2nd DD all you would have to do is disengage the OD.
    However, some folks like to use OD as a fourth gear. E.g. 1st, 2nd, 3rd, 3rd w/ OD. This is the same concept used on modern cars such as a 5 speed transmission. Where the 4th gear is a 1:1 ratio. (For every rotation of the crankshaft, the output shaft of the transmission makes one rotation.) Then the 5th gear would act as 4th w/ OD. Where the ratio would be X:1.

    How does OD work?
    For starters, below are six pictures. These are taken out of the Borg-Warner manual linked below. Pages 8, 9, and 10.
    Click image for larger version

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    This is the Sun gear assembly (Above). When OD is engaged the power goes from the Sun gear (center gear) into the three pinions, then into the ring gear (Outermost gear). Then from the ring gear it goes to the output shaft.
    Click image for larger version

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    Above are two examples in one picture.
    On the left we have OD available/disengaged. When OD is available the pawl rests on the blocking ring. Allowing the Sun gear-control plate to spin.
    On the right we have OD engaged. When OD is engaged the pawl is now in between teeth on the Sun gear-control plate. The control plate is now stationary.
    Click image for larger version

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    Above we have OD unavailable. The tab on the lower right (of the above picture) is pointing towards the solenoid.
    When OD is unavailable the control shaft and the control fork are shifted backwards, making the Sun gear to connect with the lockup teeth. This makes all the gears move as a unit. Making the ratio 1:1.
    Click image for larger version

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    Above we have two pictures. When the OD is available the tab on the bottom right corner is pointing away from the solenoid. This enables the solenoid to move the pawl from the blocking plate to the Sun gear-control plate, effectively engaging OD (Above Left). This then delivers the power (as explained on the top picture) to the Sun gear to the output shaft.
    When OD is available but disengaged (Above Right) the power is applied directly to the Freewheel unit. (Pictured below)
    Click image for larger version

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    Above is the Freewheeling unit. Freewheel unit is not the technical term, but for convenience I will refer it as such.
    Again, freewheeling is when OD is available, but disengaged.
    The power is delivered directly into the Freewheel cam. When driving torque (driving torque is when the accelerator is pressed) is applied the clutch rollers (contained within the roller cage) are pressed out against the outer race. From the outer race the power is delivered to the output shaft.
    When coasting (accelerator is not being pressed) the clutch rollers are released and are no longer holding the outer race. This allows the clutch rollers, mainshaft, and engine to rotate at a slower speed then the ring gear and output shaft.

    Parking w/ OD! PLEASE READ!
    Parking w/ OD is a little different than normal. If you have OD available then you want to put your car into Reverse. This will prevent your Studebaker from rolling away. No one wants that to happen.

    I've taken this knowledge from various posts on this forum, along with the manual for the OD.
    If you would like to read it the manual click here:
    http://www.tocmp.com/manuals/trans/B...rive/index.htm
    It explains what it is, and how it works. Much a deeper take then this post.


    A special thank you to everyone who helped me create this post, and to Mark Wheeler for linking it on the SDC website.
    I couldn't have done it with out you.
    Last edited by '66Commander; 09-27-2013, 01:07 PM. Reason: Putting most recent info on top post.
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