Does my 99 4EAT have overdrive?

[harrymaneuvers]

I didnt think our cars did?!?!


When going up a hill in 4th... my car will start to slow due to the incline. But if I dont press the pedal hard enough to drop it into 3rd, but instead just let the incline start to slow the car, at some point it drops into what seems like is a "special gear" that the tranny "downshifts" to and raises the RPM's by about 500 but it actually isnt going into 3rd...


I made a quick video to show... look at :18 you will see my car jump up about 500 RPM which REALLY helps climb this incline that I am driving up...

But it isnt a full downshift to 3rd, which I do a few seconds after the RPM's go up just to show the difference between what is happening and what happens when it is dropped into 3rd... It is weird... like it is a 3.5 gear or something.

http://www.youtube.com/watch?v=Lx_81FLE ... ture=g-upl (http://www.youtube.com/watch?v=Lx_81FLEF2k&feature=g-upl)



Is this the Torque Converter kicking on/off? I have power mode wired but it would do this before the power mode wiring too.

[StatGSR]

video is set to private, cant view it....

[harrymaneuvers]

Fixed

[Wiscon_Mark]

That's the torque converter unlocking. Don't know if the torque converter locking is synonymous with overdrive or not, but yet, the 4EAT does have a "5th gear" so to speak.

[02_Legacy]

ya definitely the torque converter clutch (TCC). When it is engaged the torque converter is locked in so transmission input is the same as engine output. When it is disengaged they can rotate at different speeds so more power (from the higher rpm) can be transferred through the torque converter.

The definition of an overdrive gear is basically one that is geared so tall that you will never be able to reach maximum engine speed (redline) in that gear because the engine does not have enough power. So go to a race track :smt002 and accelerate till you can't go any faster, if you are at redline, no you don't have overdrive, if you are somewhere short of redline then yes there is an overdrive. Of coarse I don't think you care that much lol.

[harrymaneuvers]

I am more so wondering how I can put a switch in to control the locking/unlocking of said TCC so it is not just up to me massaging the pedal in just the right way.

[greentowtruck]

This may be my first post on here but I am an ASE certified tech.

An overdrive is a gear ratio that is higher than 1:1 so that the drive shaft / pinion gear of the differential turns faster than the engine rpm therefore lowering the rpm of the engine at highway speeds. Because of this there is no torque multiplication as you see in the lower gears. That is why you don't seem to have any power in 4th (or 5th with the 5 speed) torque is what is needed for getting up hills, pulling, and launching off the line.

he gear ratios for the 4EAT are
1st 2.785
2nd 1.545
3rd 1.000
4th 0.697
Rev 2.272

So the 4th gear in the subaru is an overdrive as the engine will turn 0.697 revolutions for every 1 revolution of the differential pinion gear.

As far as torque converter lock up, it is used to lock the converter internally to act more like a clutch on a stick, it should only activate when running at steady speeds. When the computer senses that the road speed and engine speed are not matched it will disengage. With it disengaged it becomes a fluid coupler and will allow the transmission to shift and idle while the transmission is still in gear.

In old automatics before computer control there was no lockup in fact without lockup there is no mechanical connection between the engine and the transmission gears. The viscosity of the fluid inside the torque converter running between the fins is enough to transmit the power from the engine to the transmission.

[Wiscon_Mark]

In old automatics before computer control there was no lockup in fact without lockup there is no mechanical connection between the engine and the transmission gears. The viscosity of the fluid inside the torque converter running between the fins is enough to transmit the power from the engine to the transmission.

That's the reason that older autos didn't get very good gas mileage, and the reason why a stick won't get as good on the highway as an auto, but better in the city. Power transfer.

[harrymaneuvers]

Good to know... Even more reason why a 4EAT is practical for me... I drive from Sacramento to Portland about ever 6-8 weeks.