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

['66Commander]

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.

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.

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.

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.

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)

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.

[41 Frank]

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.

[BobPalma]

Good idea! Corrections / Notes in RED:

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 3^rd 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

[wittsend]

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

[9echo]

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.

[StudeRich]

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.

[StudeRich]

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.

[sactorandy]

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

['66Commander]

[wouldn't it be "by 30%," rather than "to half?"]

That is what I would have thought too. But according to the Borg-Warner manual it is by half. (Page 6 Section 2. Comfort, bullet b.)
Strange right?

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

Exactly. I do not know the mechanics of it my self. I also statred this string so I can learn how to use OD myself.

So, here we go with revisions:So what is Overdrive?
Overdrive changes the gear 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.
For an example of 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.) Now this may vary from car to car. [This may not be very important to how it works, but it was in the Borg-Warner manual. I figured it would give a brief explanation of what it does.]

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?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 leave it available to them.
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 brakes you want to ensure OD is disengaged, and unavailable, just to make sure. When OD is enable the transmission is freewheeling. And will not have engine brake capabilities. Be careful.

Parking w/ OD! PLEASE READ!
Parking w/ OD is a little different than normal. If you have OD engaged 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.

[gordr]

[greyben]

My 1955 owner's manual gives a clear and concise explanation on how to use overdrive covering all modes of operation. Since overdrive operation remained the same from about 1939 through the end of production it is assumed that all relevant owners manuals would give the same description. The shop manual gives a good description of the mechanical operation. If you had access to the planetary gear assembly it would be even clearer.

I believe the actual gear reduction ratio is 0.72 although this was frequently referred to as approximately 0.7

[omstude]

Ah, overdrive, what a great transmission! Yes, the owners manuals are quite good and concise about explaining how to operate overdrive. It's really not hard when you get the hang of it. I basically learned to drive on my 52 Land Cruiser so it's second nature to me. The only way real damage can result from operator error is if you don't know how properly to lock it out while driving. I once had the brakes fail on my 52 while descending a steep hill in a suburban area with the overdrive engaged. I was freewheeling so I had to accelerate enough to engage the transmission in third gear, pull out the overdrive lever, downshift to second, pull the parking brake as hard as I could and leave most of my right front tires white wall on the curb in order to stop.

['66Commander]

(Quotes from other folks are further down)

Some suggested edits inserted

(Questions/comments I have to some revisions are numbered in the quotation box below)

1: With the 1st w/ OD some people say that they always have OD on. Even in 1st gear.
What is the problem if it is in 1st w/ OD? Perhaps I can add a warning?
2: How come?
3: I'm trying to make this kinda simple. I'm not going to lie, when I first started with my Studebaker, I wouldn't have know what "an extra planetary gearset" would mean. Granted, most people who work on cars know what this means. But I just want to try and cover as many bases as I can.
4: Why not? On one of the posts on this forum (I can't remember what one) it said that this isn't necessary, but it helps prevent wear.
5: I do like this sentence. However, how would this take effect? According to the Borg-Warner manual it says that it will disengage by itself.
I'm on the fence on if I want to use enabled v. available. Because, to me at least, enabled means it is on. Where as available means the option is there. What is everyone else's thoughts?

Thank you. The revisions I used are highlighted red.

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


This is commonly known as "overdrive locked out".

in overdrive gear. E.g. 1st w/OD *see quote above*, 2nd w/OD and 3rd w/OD.
and the transmission's free wheeling is in effect, meaning no engine braking. E.g. 1st, 2nd, 3rd.

may engage, if it is available". This speed is 20 to 32 mph. (Depending on make/model)

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?

all the way out.
To engage OD ensure that OD is available (knob in), and when at or above cut-in speed; briefly release the gas pedal. You will be able to hear the RPMs drop. And then drive as normal from there.
To disengage OD simply press the gas pedal all the way to the floor to activate the kickdown circuit. This will drop the car back to DD third (no overdrive), raising the RPMs, disengaging OD. You would do this, for example when passing another vehicle, or ascending a steep hill.cut-in speed the OD will automatically disengage itself.

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.

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.

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

I have thought about that, but I decided to make this more about the bare-bones and how it works. Also, I'm not familiar with how it works itself. I actually started it because I was researching a correct way to use it. But if a couple more folks think it would be beneficial to have that explanation, I am more then willing to do it. Or if I have enough free time haha.

Ah, overdrive, what a great transmission! Yes, the owners manuals are quite good and concise about explaining how to operate overdrive. It's really not hard when you get the hang of it. I basically learned to drive on my 52 Land Cruiser so it's second nature to me. The only way real damage can result from operator error is if you don't know how properly to lock it out while driving. I once had the brakes fail on my 52 while descending a steep hill in a suburban area with the overdrive engaged. I was freewheeling so I had to accelerate enough to engage the transmission in third gear, pull out the overdrive lever, downshift to second, pull the parking brake as hard as I could and leave most of my right front tires white wall on the curb in order to stop.

It definitely will become easier once one gets the hang of it. But til then it can be confusing. Least for me it was.
Oh wow! I'm glad that you and your Stude are okay. Kinda reminds me of when I found out that my brakes and parking brake didn't work... the hard way.

[wittsend]

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


Statement by 66 Commander: "Exactly. I do not know the mechanics of it my self. I also statred this string so I can learn how to use OD myself. "

----

My apology. It was stated in post #1 "Again, please let me know of any corrections I should make, or any suggestions." The intention of my post was to simply say I didn't under the Cut-in Speed. If I understood HOW it worked then I might understand the application of the function. Some of us learn that way. As a "suggestion" I felt it was self evident.

The original post also included a "basics" of the overdrive. I took it to mean this was not (just) a discussion amongst "those in the know"..., but an attempt to enlighten those who didn't. Like me. I was simply trying to learn. Not be disruptive.

Tom

['66Commander]

No worries.
Sactorandy asked about it too.
Today is busier then normal today at work, but I will do some studying. When/if I get it written up I'll add it onto the post.