97 OD trans shift

[corvetteguy]

In my 97 3 speed auto OD I can see/feel 4 shifts when running in OD. Should I also feel another shift as the torque Converter locks up? When does that happen?

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[Mark Kovalsky]

You have three shifts plus the torque converter lock. 1-2, 2-3, 3-4, and the torque converter lock. That's four events, there are no more.

[corvetteguy]

I thought "Overdrive" means that the trans is
actually over driving the motor speed. In other
words the drive ratio is less than 1:1 (OVERDRIVE).
You mean for Ford this is not true?

If you can "lock out" the overdrive with a
switch on the shifter. How does an
electrical circuit get to a spinning
Torque Converter? There can't be
electrical connections to the spinning hub.

I'm confused.

[Mark Kovalsky]

Overdrive and the lockup torque converter are two separate things.

Overdrive is indeed a gear ratio that is higher than 1:1. It's 0.70 in your trans. The overdrive gear is inside the transmission, not in the torque converter. When in overdrive the engine is spinning 0.7 times for every revolution of the driveshaft.

When the torque converter locks up it is done hydraulically, not electronically, at least at the torque converter. When the torque converter is locked the input and output speeds of the torque converter are the same.

There's a lot more info on how all this works at www.howstuffworks.com.

[LastSplash]

3rd gear is 1:1 and 4th is the OD, the reason you dont feel the TC lock up is because under light loads the TC locks at almost immediately after the 3-4 shift, you can see the TC lock by watching the tach and letting off the gas then lightly pressing the pedal again above 45mph, the RPM should go up then drop a little as the TC locks up.

[Bluegrass]

Additionally, the lockup is on and off many many times as you drive.
The throttle has almost exclusive control because as you lift the throttle the lockup goes off much of the time because you don't want the motor driving the truck during an emergency brakeing situation and lengthening stopping distance.
All lockup converters are intended to operates this way.
First ones I remember are in the Bronco II as far back as 1984 in the A4LD transmissons..
Some people put manuel switching in place to overide this but it's not really much of a benifit because you have one more thing to keep track of because you can't leave it on all the time.
There are times that it should not be locked up under hard pulling because it is not intended to pass full motor torque to the load.
A diesel has mutiple discs in place to handle additional motor torque but still is subject to the same laws.
I have a diesel converter in my custom 4r70 just for pulling heavy gross loads.

[corvetteguy]

I think I got it.
You guys are helpful.
Now what is happening on my 84 corvette
with 4+3 manual transmission.

There is a button on the shift that will
modify geer 2,3,4 to a 1/2 geer higher
under almost any condition. Ir this
some form of overdrive in the manual
geerbox?

[glc]

Yes, that controls an old style separate overdrive unit that's behind the transmission. I had a 80 Volvo that had that, but it would only work in 4th.

The original overdrives on manual transmissions date way back to the 50's and probably earlier. They were separate units bolted on the back of a standard 3 speed manual. They were engaged by lifting your foot in 3rd at over 25 mph, and could be locked out with a knob on the dash. They also had a full throttle kickdown switch that would drop it out if you floored it, and would automatically drop it out when speed went below 25 mph. They would not engage in 1st or 2nd.

Today's overdrives, both on automatics and manuals, are simply an additional gear in the tranny with an "overdrive" ratio of less than 1:1. 3rd in your automatic is 1:1 and 4th in the M5OD is 1:1.