auto trannys with Overdrive... why they die? - Toyota Nation Forum : Toyota Car and Truck Forums

nsol357 · 04-09-2002, 09:57 PM

Hey, hope this is technical enough to qualify posting in this forum :grin:

Anyway, I read a thread in the Vortex here:
http://forums.vwvortex.com/zerothread?id=316579
(Yeah, I think the mods should label me as the VWVortex cross-post whore :grin: ) and I'm curious as to why I keep hearing stories from people saying that driving in OD is bad for the car. My dad tells people to drive in OD all the time. Any of you TN'ers can shed some light on this topic?

bondobondo · 04-09-2002, 09:58 PM

nsol you cross post whore.

nsol357 · 04-09-2002, 09:59 PM

Hahaha
just answer the damn question Andrew! :razz:

bondobondo · 04-09-2002, 10:16 PM

OD is bad for the car -

if you are not driving fast enough.

what happens is that the gearing ratio is negativly set against the engine, increasing load that is upon it.

like you are always lugging the engine.

If you are driving fast enough, OD will only kick in once this speed is reached on an automatic.

if you disable OD on your automatic you will see that at hwy speeds (and only hwy speeds) your tach will read alot higher than normal because your car is missing its 4th and on higher class trannies 5th gear, which is the OD gear.

think about 2 circles,
the engine is the larger one, and the tranny is the smaller one. and they spin together.

now with OD, the smaller wheel is larger, than the engine, hence the engine has to work harder to turn it. for every 1 rotation of the engine wheel, the drive wheel only goes around 3/4 times, for argument sake..

you are always running at a ratio that is lower than that of the engine, like switching gears on a bike. so most of the time you are at a ratio that is lower than that of the engine. but at hwy speeds, since
1. load on the car travelling at 100km/h is much less than say 50 km/h and it takes alot less power to keep it moving at 100km/h (ideal conditions: minimal wind, slope, etc) so OD is an effecient gear that will still allow enough power to keep the car at that speed.
under non-ideal conditions like driving thru the rockies or anywhere where there is long durations of inclines, you will see signs that tell drivers to turn their OD off. This is for that very reason that OD will terminate your engine due to the excess load and strain forced upon it.

Usually at high speeds and compensating ecu trickery, OD has hardly any effect on the engine, since the ECU will control when the od will kick in and it is usually at an rpm that is well withing a decent torque range, and hp level as well.

anytime you would try to agressively pass someone on the hwy your engine will downshift because od is not powerful this way...

ramble ramble..

_________________
Andrew Lee
ae92 Trueno

[ This Message was edited by: trueno92 on 2002-04-09 22:18 ]

nsol357 · 04-09-2002, 10:51 PM

Now THAT'S the kind of answer I was looking for. Thanks!

Errr... mind if I post this to VWVortex to share w/ my fellow dubbers? LOL :grin:

(Let the cross-post whorage continue! :roll

_________________
nsol357

Don't have a Toyota...
heck! I don't even own a CAR! :razz:

[ This Message was edited by: nsol357 on 2002-04-09 22:51 ]

92CAMRYGTS · 04-10-2002, 11:44 AM

well i have a friends that is a mechani at a toyota deale and he told me to keep the car in O/D. i'm not sure why but thats what he said. i figured it would lessin the wear on the engine and tranny cause it would keep the car at lower RPM's

AzimuthX · 05-02-2002, 01:08 AM

Back than my dad used to turn off OD in local roads because his priv mechanic told him to (also when my dad told him the camry is dying [weak sh*t]) Anyways I always like the feel when OD is off especially entering the highway, on the 01 Camry LE, it shifted at 6k (dad was pissed off at this slowpoke) with OD disabled.

Anyways what will I say to my dad? Disabling OD is a good thing in local driving (up to 80-100?) When should a 92 Camry Le 4 should turn on OD ? He says it wrecks the engine because the RPM is 1-1.5K more than normal.

F1 Chris · 05-02-2002, 04:05 AM

My dad told me overdrive helps turn the engine slower (lower rpm's) and increases gas mileage, extending the life of your engine. it's just FOURTH GEAR! hahaha!

This is why I manually shift the car, because I like to have it shift at 3-3.2k rpm and keep the engine from lugging...EVER, but especially up the hills. going up a hill at lower than 2.5k rpm overworks the tranny and heats up the fluid. I only turn on overdrive on the highway or when the road is flat and over 45mph, but in the city i'll keep o/d off to keep the tranny from making too many shifts.

Dark · 05-02-2002, 01:42 PM

My dad had a 90something chev. silverado and went through something like two trannies from years of pulling a 250gallon water tank behind his truck in OD. so if youre towing anything take the OD off!!

Xenon · 05-02-2002, 02:04 PM

You know what! There's alot of Mechanic that have oposite opinions of others.

Another Automatic gear issue that I had with my dad's car was that some mechanics tell you to put your gear on N when you're stopping on a traffic light or just parking with the car on, he claimed it would take the stress off the transimission...

Now another mechanic said that was B.S. because when you put the gear in N the transmission oil goes down to the tray leaving the gear almost dry, and when you put it back in gear the oil won't insantly go back to the gears, so that would wear out your gears in time!

I personally agree with the second opinion. leave your gear in place because I'm sure that when they built cars they did take this in consideration.

_________________
Xenon

1990 Corolla SR5

[ This Message was edited by: Xenon on 2002-05-02 14:05 ]

tAn_CamRy · 05-21-2002, 08:23 AM

what i don't get is why isn't there a clear answer?

Xenon · 05-22-2002, 02:26 PM

You know I just drove my cousin's 2000 Camry SE (4 Cilynder) and it has an automatic O/D button! Meaning everytime I turn it off while driving, when you start the car again it will turn on automatically!! Now why would Toyota have it on all the time if it's bad for your engine?

Could anyone explain that??

***Phi*** · 05-22-2002, 03:05 PM

Quote:

when you start the car again it will turn on automatically!! Now why would Toyota have it on all the time if it's bad for your engine?

Not sure why your cousin's Camry does this. None of our 3 Camrys display this odd behaviour.
If it does infact do this, the Toyota engineer don't necessarily have the benifit of the engine in mind. I think it has more to do with making it as "fool-proof" as possible for the public. Who many "lay-men" do you know that would be smart enough to switch O/D on and off to correspond with the traffic there driving in? Try explaing OD gear shifting to a 56yr old grandmother :roll:

Xenon · 05-22-2002, 07:09 PM

I know, it just didn't make sense! I remember back when I used to be in Iraq my father had a 1986 Toyota Crown Super Salon (I don't know if you guys are familiar with these cars!) it was 2.8 litre Automatic with O/D but the button was manual! So when you push it, it would go off and won't come on until you push the button again!

This button on the 2000 Camry is Automatic reset, meaning when the car is turned off and back on, the O/D will be activated again! And the red light that tells you O/D off on the dash would mean that it's a bad thing (And that the factory setting is on ON)..

So I don't know why they'd do that?!