SHIFFTING INTO OVERDRIVE

[Sactownog]

I am running a 1939 Dodge 3-sp with O/D unit. 

 

There is a push/pull mechanism behind the solenoid that engages or disengages the Overdrive function. 

 

My question: when the push/pull mechanism is forward (toward engine) is that when the OD is engaged? or is it when the lever is towards to back of the vehicle (towards the rear of the vehicle)?

 

There is also a button that I am told I hit to (Step Down) the OD. so if I am in 3rd gear with the over drive engaged and I am going up a hill and need more speed, that I can hit the button and shift into 2nd gear OD to help push car more easily up the hill. 

 

all help is appreciated. 

[Matt Harwood]

Pushing the knob in is typically the ON position for the overdrive. Not always, but usually. Start there.

 

HOWEVER, this knob is not to be considered simply an ON/OFF switch. Pushing it in will not immediately engage the overdrive and pulling it out at speed can damage the unit. Don't do that.
 

Instead, what pushing the knob in does is make the overdrive ready to shift into overdrive; the solenoid does the actual shifting, not the knob or lever. Pushing the knob in will activate free-wheeling, so if you are in 3rd gear and it feels like you are coasting in neutral, you know you're in free-wheeling mode. Once you are in free-wheeling mode, you activate the overdrive by accelerating to more than about 30 MPH in 3rd gear (or even 2nd, but start with 3rd gear until you get to know it) and then VERY ABRUPTLY lift off the accelerator pedal. I mean, just pull your foot off the pedal. Not gently, not gradually--just snap the throttle closed. If the overdrive unit is working correctly, you will feel something akin to an automatic transmission shift and free-wheeling will end. You will be in overdrive.

 

I find that 2nd gear + overdrive is a great around-town gear and if yours is factory-installed, it will have an automatic kick-down that will take it out of overdrive when you slow down sufficiently. Speed up again, lift off the pedal, and it will go back into overdrive. It was designed to cut down on shifting around town and works rather well that way. 3rd gear + overdrive will carry you at 60-65 MPH.

 

I don't know about the button and the step down, but it might just be a manual override to take it out of overdrive--they may have removed the governor that did it automatically when you slow down. Experiment and see what happens when you push it while in overdrive. It probably kills power to the solenoid, releasing the overdrive and going back into free-wheeling/non-overdrive mode. You'll feel it.

 

But the single most important thing (and the part most guys don't get) is to accelerate to speed with the knob in free-wheeling mode, then quickly and abruptly lift off the accelerator. Most people don't understand this part, but the clutch sprag in the overdrive needs a bit of backlash to lock up the overdrive's planetary gears. If you do it too gently or at too low a speed, nothing will happen. You'll know you're in overdrive because you will have engine braking again, even though it will be slight in overdrive. It won't be like free-wheeling which feels like being in neutral. If you don't have free-wheeling, then it will not shift into overdrive--most likely culprit is having the overdrive lever in the wrong position or not fully pushed in or pulled out.

 

Also, while the instructions say you can take it in and out of free-wheeling mode while moving, I find that it's harsh and borderline abusive to the hardware, and never, ever do it while the overdrive is engaged. I recommend only doing it while sitting still. On factory installations, reverse gear should work regardless of the overdrive knob's position, but if you find that you have no reverse gear, pull out the overdrive knob, which will disengage free-wheeling and allow the one-way clutch in the overdrive unit to lock up and reverse should work again.

 

Hope this helps.

[Sactownog]

3 hours ago, Matt Harwood said:

Pushing the knob in is typically the ON position for the overdrive. Not always, but usually. Start there.

 

HOWEVER, this knob is not to be considered simply an ON/OFF switch. Pushing it in will not immediately engage the overdrive and pulling it out at speed can damage the unit. Don't do that.
 

Instead, what pushing the knob in does is make the overdrive ready to shift into overdrive; the solenoid does the actual shifting, not the knob or lever. Pushing the knob in will activate free-wheeling, so if you are in 3rd gear and it feels like you are coasting in neutral, you know you're in free-wheeling mode. Once you are in free-wheeling mode, you activate the overdrive by accelerating to more than about 30 MPH in 3rd gear (or even 2nd, but start with 3rd gear until you get to know it) and then VERY ABRUPTLY lift off the accelerator pedal. I mean, just pull your foot off the pedal. Not gently, not gradually--just snap the throttle closed. If the overdrive unit is working correctly, you will feel something akin to an automatic transmission shift and free-wheeling will end. You will be in overdrive.

 

I find that 2nd gear + overdrive is a great around-town gear and if yours is factory-installed, it will have an automatic kick-down that will take it out of overdrive when you slow down sufficiently. Speed up again, lift off the pedal, and it will go back into overdrive. It was designed to cut down on shifting around town and works rather well that way. 3rd gear + overdrive will carry you at 60-65 MPH.

 

I don't know about the button and the step down, but it might just be a manual override to take it out of overdrive--they may have removed the governor that did it automatically when you slow down. Experiment and see what happens when you push it while in overdrive. It probably kills power to the solenoid, releasing the overdrive and going back into free-wheeling/non-overdrive mode. You'll feel it.

 

But the single most important thing (and the part most guys don't get) is to accelerate to speed with the knob in free-wheeling mode, then quickly and abruptly lift off the accelerator. Most people don't understand this part, but the clutch sprag in the overdrive needs a bit of backlash to lock up the overdrive's planetary gears. If you do it too gently or at too low a speed, nothing will happen. You'll know you're in overdrive because you will have engine braking again, even though it will be slight in overdrive. It won't be like free-wheeling which feels like being in neutral. If you don't have free-wheeling, then it will not shift into overdrive--most likely culprit is having the overdrive lever in the wrong position or not fully pushed in or pulled out.

 

Also, while the instructions say you can take it in and out of free-wheeling mode while moving, I find that it's harsh and borderline abusive to the hardware, and never, ever do it while the overdrive is engaged. I recommend only doing it while sitting still. On factory installations, reverse gear should work regardless of the overdrive knob's position, but if you find that you have no reverse gear, pull out the overdrive knob, which will disengage free-wheeling and allow the one-way clutch in the overdrive unit to lock up and reverse should work again.

 

Hope this helps.

That is the most information I have been given about a transmission ever, let alone the one that I have. Thank you VERY much. I have found that Disengaged OD is when the lever is towards the engine (I.E. when the knob on dash is pulled out towards driver) and when the knob on dash is pushed in that it will engage the transmission OD. 

 

as you mentioned above, "likely culprit is having the overdrive lever in the wrong position or not fully pushed in or pulled out." so I plan to set the lever with the dash knob pulled out (disengaged) and start from there with hopes that it will allow me to push in the knob and fully engage the OD. 

 

again. Thank you for this awesome amount of help. this info should be stickied somewhere on this forum. 

[Frank DuVal]

Lucky I owned/drove a 50 Champion in college with OD, so I kind of knew how it worked, but I found NO information on how to drive the Mechanical OD in my 38 Graham. No electronics! No solenoid, no switches, just use the accelerator pedal like Matt says. Works quite well, though.

[Sactownog]

my 39 does have an electric solenoid. 

[Buffalowed Bill]

Speaking for Studebakers, that I know a little about. The first Warner OD's were referred to as "automatic overdrives," that is that they were either in or out of OD, and could not be locked out after a certain speed was obtained and the driver let up on the accelerator. The early (1934-37) trans could not be locked out of OD. In 1937 Studebaker finally got an optional trans that had a mechanical, cable operated OD, with which the driver was now able to lock the trans out of OD, but still no electrical function. It seems as though nearly every year there was another iteration of the transmission. In 1939 the electrical function was introduced, which allowed for the driver to floor the accelerator, to down shift (passing gear). The electric kick down, like your car has, really provided the last required layer of improvement to make the OD equipped cars a real delight to drive. 

[Sactownog]

56 minutes ago, Buffalowed Bill said:

Speaking for Studebakers, that I know a little about. The first Warner OD's were referred to as "automatic overdrives," that is that they were either in or out of OD, and could not be locked out after a certain speed was obtained and the driver let up on the accelerator. The early (1934-37) trans could not be locked out of OD. In 1937 Studebaker finally got an optional trans that had a mechanical, cable operated OD, with which the driver was now able to lock the trans out of OD, but still no electrical function. It seems as though nearly every year there was another iteration of the transmission. In 1939 the electrical function was introduced, which allowed for the driver to floor the accelerator, to down shift (passing gear). The electric kick down, like your car has, really provided the last required layer of improvement to make the OD equipped cars a real delight to drive. 

I am getting more and more excited to drive this car again, especially with the OD. Praying it works properly. 

[ojh]

Dunno about all OD units but the one I'm doing right now ('52 Nash-Healey) is very sophisticated electrically, connecting to the ignition coil and engine vacuum   When you push the OD knob 'In' it allows the system to work, when you get just under 30mph the overdrive governor points close and send power to the OD relay, if you lift you foot the OD kicks in and interrupts the ignition circuit to engage the OverDrive and the dash indicator light comes on.  The coil interface thru the vacuum  is especially important when freewheeling downhill to avoid excess fuel in the exhaust to ignite when you come back on the throttle.

 

[Grimy]

A very important consideration:  Each OD has a threshold speed at which the driver may let off the accelerator and the OD will upshift while the OD is cable-engaged; the threshold varies by car (e.g., my 1948 Jeepster and previous 1948 LC both with electric controls like yours including kickdown have a threshold of about 30 mph, but my 1936 Pierce with no electric controls is 40-42 mph), and BELOW the threshold the car will freewheel (i.e., no engine braking).  You must be mentally prepared for the "Oh sh*t" moment when you come to a sudden, steep downgrade where you need engine braking but are below the threshold speed.  If you declutch and attempt to pull the handle out to disengage the OD to acquire direct drive, you will likely be unable to do so UNLESS it's a short moment after positive acceleration.  The solution is counterintuitive:  despite the urgent tendency to brake, you must accelerate MOMENTARILY to make the engine drive the trans, then almost simultaneously let off the throttle, declutch, and pull the OD handle out.  This is a much more severe emergency on cars with high threshold speeds, as this story illustrates:

 

In 1994 the immediate previous owner of my 1936 Pierce was southbound on I-5 cresting the Siskiyou Summit at the OR-CA border.  The California side is a 6-7% downgrade for about seven miles!  That car has a 40 mph OD threshold.  He was behind a truck climbing the OR side of the summit and the trans dropped into direct automatically when he dropped below the 40 mph threshold.  He crossed the peak and began the downgrade.  Because he had not throttle-accelerated (increasing the input-shaft speed) to above 40 mph, the trans remained in free-wheeling mode, and the 6,000 lb car + two people and their two weeks of baggage hurtled downgrade, gathering speed with NO engine braking.  He tried to declutch and pull the handle out but could not, causing a lot of grinding (and breaking off a couple of dogs on the unobtanium clutch gear in the OD).  He glazed the brake shoes but maintained control--barely--all the way down the hill.  And that's when he decided to sell the car to me...  If he had accelerated momentarily, he could have either (1) caused the car to upshift to OD-engaged-with compression-braking, or (2) declutched and pulled the handle out to achieve 3rd-direct-with-compression-braking.

 

Over the years, I've had a couple of "surprises" under similar--but not nearly as drastic--circumstances, but was mentally prepared for what I had to do to achieve control.  His story of that experience remains in my memory.

[Grimy]

@Sactownog  An answer to your other thread while I'm thinking about it on adjusting the OD cable:  (You will need a helper) Disconnect the cable from the OD lever on the trans.  Manually operate the lever to its two extremes (OD and direct drive) and temporarily mark the trans case with each location.  The idea is to adjust the cable and its bracketry so that you achieve FULL lock on each side.  Attach the cable while the trans is in OD.  Then your assistant declutches and operates the knob fore and aft while you are under the car inspecting and assuring that each of the two full lock positions is achieved.  This needs to be done whenever a trans has been out, and if you're having trouble with the system in other circumstances.

Edited July 9, 2020 by Grimy
corrected typo (see edit history)

[JACK M]

Its a technique.

Once you use it awhile  you will find yourself putting it in and out often.

[Ed Luddy]

My old 1966 Studebaker Commander has O/D, Borg-Warner I think. It helped the 194 c.i. GM sourced inline 6 maintain highway speed without over revving. Lever control, took some time to figure out, but I sold the car before I really got the hang of it.

[JamesR]

On 7/8/2020 at 4:07 PM, Matt Harwood said:

 

HOWEVER, this knob is not to be considered simply an ON/OFF switch. Pushing it in will not immediately engage the overdrive and pulling it out at speed can damage the unit.

 This is very true. Don't ask me how I know.

 

I don't know about the OP's Dodge, but the original owner's manual that came with my '54 Ford was generally inadequate in explaining to drivers what NOT to do with OD units. There were literally no warnings about pulling out the OD knob at speed.

 

Some other limitations and cautions (depending on your unit): Some people will recommend just keeping the OD "on" (knob pushed in) all the time with units that have a governor that "locks out" (disengages) the overdrive when the car's speed gets below a certain level. Though I drove this way for a while, I don't do it anymore, and would not recommend it. While it's true that the  governor is automatically activated, if the governor ever gives out (as parts often do) you won't likely be aware of it immediately, and starting out in low gear or going into reverse WHILE IN OVERDRIVE when the governor is out might wreck some internal parts like needle bearings. Replacing a governor on many OD units doesn't involve removing the transmission/OD from the vehicle and disassembling it, but wrecking needle bearings will...and you don't want to go there. Also, keep in mind that old cars with primitive drum brakes kind of partially relied on "engine braking" (what happens when the car is not in overdrive) to help the brakes slow the car down. Having free wheeling or reduced engine braking can put a bit more stress on the wheel brakes and make them wear out a little earlier, and it's maybe a little less safe, too.

[Sactownog]

THOSE WITH O/D UNITS! 

 

do you put the button to shift up/down on the floor to use your foot or do you put it up on the dash to use your hands? 

 

the button that helps shift from 3rd to 2nd and stay in OD? 

[Bloo]

I don't have an overdrive anymore. I have had some in the past. My favorite was in a 51 Nash Statesman. I just left it in overdrive (cable in) most of the time. Drive like a normal stick, lift foot in high, clunk... its in overdrive. It had a switch on the throttle linkage. Now Nashes like mine had a cable-and-pulleys sort of throttle linkage, and the switch was a momentary thing with a cable hanging out of it connected to the throttle linkage.

 

To the driver it was just like kickdown on an automatic transmission, you just might want to pay a little more attention to the speed you are going and the gear you might wind up in if you floor it.

 

That switch with the pull cable had 2 sets of contacts, but I don't remember what the second one was for. Maybe it cut power to the solenoid.

 

When you floored it, one set of contacts shorted the ignition points out. This would cut the engine, taking the mechanical load off of the overdrive solenoid, releasing it. When the solenoid released and bottomed out, it would hit another set of contacts in the back of the solenoid, removing the short and thereby turning the ignition back on. This all happened so fast as a driver you would never know it killed the engine for a split second.

 

[JACK M]

10 hours ago, Bloo said:

When you floored it, one set of contacts shorted the ignition points out. This would cut the engine, taking the mechanical load off of the overdrive solenoid, releasing it. When the solenoid released and bottomed out, it would hit another set of contacts in the back of the solenoid, removing the short and thereby turning the ignition back on. This all happened so fast as a driver you would never know it killed the engine for a split second.

 

Mine was under the foot feed.

Like Bloo says, stomp on it and its just like a passing gear. (Regular third gear/no OD) Lift and it goes right back into OD.

[Sactownog]

I need to know where I should put the shift button (black button that i hit for shifting from 2nd or 3rd OD) is it a foot button or something that should be on the dash to allow me to shift from 3rd OD down to 2nd OD???? opinions wanted. 

[Grimy]

In stock form, the kickdown switch for an electrically-operated OD is a plunger-type switch under the accelerator pedal.  If you can find such a switch, I'd use that--because it's hands-free.  Just push the accelerator hard (i.e., floor it) and the kickdown occurs.

 

BUT that's going from 3rd OD to 3rd direct, or from 2nd OD to 2nd direct.  Up and down between 2nd and 3rd is done without any switch, **IF** you're above the threshold speed which should be about 30.