Is "Overdrive" still relevant?

[SZR48207]

I think I fall bit under the median age of BITOG, as most members here seem to be in their 30s and up. I guess I mention this as a preface to my naivety in this question.

Does it actually matter any more if a car has "overdrive"? Are any manufacturers using automatic transmissions that do NOT have O/D?

Recently I've been browsing car listings out of boredom, and I'll sometimes see that "Automatic w/ Overdrive" is mentioned, but do most people even understand what this means? I'm almost inclined to believe someone who has no idea what O/D is would falsely assume it equated to "high performance". (the old phrase "shift it into overdrive")

For all intents and purposes, I am glad that the transmission in my vehicle has overdrive, as I'm sure this has helped me to get pretty decent highway MPG, but I just don't really think about the fact that I have O/D as some sort of grand feature that makes or breaks the deal w/ owning the vehicle.

 

[eljefino]

I think the lockup torque convertor was a more important development, keeping trans input power from always being partially turned into heat/slushiness.

Since axle ratios aren't talked about much, except WRT towing packages, I figure they'd be better off with a 1:1 top gear and proper final drive...

 

[Johnny]

I think the term/word overdrive may be a little outdated now since most standard transmissions are now going 5-speed and some 6-speed and most automatics are either 4,5, or 6-speeds. Back in the day is was a big deal to have that one more higher gear to go to. I had a TR4 and my best friend had a TR4A, mine was a 4-speed and his was a 4-speed with overdrive. He got a little better mileage than I did on the highway, but at the price of gas back then no one cared about mileage, but he also had a higher top end speed than I did. The old 2-speed powerglide automatics in Chevrolets were a great transmission, then they went to the 3-speed and some called that third gear overdrive. It's just one of those terms that has served its purpose and time.

 

[Shannow]

Back in the day, an overdive was often an electrically switched (Brit) thing that took your 1:1 "top" gear, adn extended it.

Brit overdrives were/are notorious for being fragile (some Volvo ones too).

Then 5th gear became standard.

Given that you can step up the gearbox, and down the final drive, or space out all gears and step up the final drive, overdrive was always a bit of a toss.

Nissan Oz sold 5 speeds with a standard bottom - top split and rear gearing in the 80.

6 speed diesels in Oz, you'd think that you were rowing them rather than driving them.

 

[SteveSRT8]

We have a show truck with a Gear Vendors unit that is just aft of the trans and is a true overdrive.

Works great with old school 4.88 gears. Stands up to 600 hp with no problems.

 

[endeavor to persevere]

Triumphs had a laycock de Normanville electrically operated overdrive. They operated in 2nd, 3rd and 4th, actually giving 7 gear ratios. I have rebuilt a few of these.

Gear ratios for a GM 4L60E..

1st 3.06, 2nd 1.75, 3rd 1.00, 4th 0.70.(overdrive)

gear ratios for a GM 6L80E...

Gear ratios:
First: 4.03
Second: 2.36
Third: 1.53
Fourth: 1.15
Fifth: 0.85(overdrive)
Sixth: 0.67 (overdrive)
reverse: 3.06

Any thing less than 1 to 1 is over drive. The new 6 speed GM trans have over drive in fifth and sixth gears.

 

[ahoier]

It's odd....cause my 07 Rio had an "O/D" button on the gearshift handle (automatic) - but, my 4cyl 08 Kia Optima did not......I don't know if perhaps the Overdrive was just "automatic" in the car, or if it just didn't have it at all My impression was O/D was more for the MPG increase, because my Rio certainly got higher MPG than my Optima Rio I maxed out at 37.29 MPG (with Shell gas), whereas the Optima I only ever got it to 29.51 with Mobil....but I had a good deal of city driving (5 mile round trip to and from school in the morning and afternoon to pick up kids...)

 

[endeavor to persevere]

I don't know of an automatic today than does not have overdrive.

The top gear is under 1 to 1 and that is overdrive.

Some cars could have a button to keep it in a lower gear. In a GM truck you just shift from Drive to 3 and you will not go to overdrive.

 

[cp3]

Your Optima had overdrive as well, basically anything over a 3 speed in production cars has overdrive. I'm not sure what the buttons do, some type of electric overdrive I assume? As shown in the post above, geared overdrive refers to the ratios in the transmission that let the input side turn slower than the output side. It reduces engine speed at highway speeds but also allows closer spacing of the lower gears for better acceleration.

 

[EricJRoy]

I have had a couple beater toyota vehicles with a 3 speed auto, and it is not cool only getting mid 20's with a 1.6l 4cyl,

87 chevy nova (corolla) bought for $40
92 Geo Prizm (corolla) bought for $200 39k orig miles

Craigslist, ebay, and higher scrap cost have meant the end of the $100 car deals, its sad

 

[JHZR2]

Why wouldnt it be relevant? It is all about physics and those laws don't change.

OD gives you higher levels of mechanical advantage. The output of the trans turns once for fewer than one rotation of the engine. This gives you, in cases where the engine can handle it, more speed for essentially less work, less fuel injection events, etc.

In an AT where there is a 1:1 direct drive gear, there were some losses, but in MT and lockup ATs, the losses are really tiny.

 

[XS650]

Originally Posted By: eljefino
I think the lockup torque convertor was a more important development, keeping trans input power from always being partially turned into heat/slushiness.

Since axle ratios aren't talked about much, except WRT towing packages, I figure they'd be better off with a 1:1 top gear and proper final drive...


Nope, it requires a bulkier, heavier transmission to get the same ratio spread if you use a 1:1 top gear. The people designing those powertrains actually know a couple of things

 

[Kestas]

Overdrive meant something a long time a go, back in the 50s. Back then most cars were designed with a final drive drive ratio of 1:1. Those owners who bought the optional overdrive enjoyed better gas mileage on our newly built interstate freeway system.

Now fast forward to the fuel crises of the 70s. I worked at Ford Transmission and Axle as a student engineer back in 1978. They were hot on a program to take the standard 4-speed (with 1:1 final drive) and turn it into an overdrive unit. They reversed 3rd and 4th gear positions within the transmission so that 3rd gear was 1:1, and gave the old 3rd gear an overdrive ratio, yet kept the shift pattern on the stick the same. But all this was mere marketing, since they also fiddled with the differential gears to give the same ultimate final drive ratio. People heard "overdrive" and immediately gushed to their friends how their new car is more efficient than their old car.

This design was maintained to this day because overdrive allows the manufacturer to package the transmission more compactly than if they made the final drive 1:1 in a 4- or 5-speed transmission. It also doesn't hurt to capitalize on the term "overdrive", even though it's now a hollow word, since efficiency really depends on the total gearing, including the differential ratio.

At the time Ford also went from a 3-spd automatic to their AOD 4-spd automatic design. I did the calculations. They fiddled with the differential and kept the final drive ratio at the rear wheels the same. The advantage was quicker pickup with the added gear and better EPA city cycle mileage.

Unfortunately, going through a gear set is a 4% penalty in efficiency.

 

[expat]

"Triumphs had a laycock de Normanville electrically operated overdrive. They operated in 2nd, 3rd and 4th, actually giving 7 gear ratios. I have rebuilt a few of these."

The overdrive would work on any forward gear, but torque multiplication would be too hard on the O/D unit in 1st (or even 2nd gears), so an inhibitor switch was built in to the electrical circuit.
The O/D must also NOT function in reverse gears due the the O/D having a one-way clutch in it's gear train.
In my opinion they were quite robust, mainly the Electrical side that caused problems (Go Figure!)

 

[SteveSRT8]

And we all know how good old British Leyland products are with electrical issues!

 

[endeavor to persevere]

Originally Posted By: expat
"Triumphs had a laycock de Normanville electrically operated overdrive. They operated in 2nd, 3rd and 4th, actually giving 7 gear ratios. I have rebuilt a few of these."

The overdrive would work on any forward gear, but torque multiplication would be too hard on the O/D unit in 1st (or even 2nd gears), so an inhibitor switch was built in to the electrical circuit.
The O/D must also NOT function in reverse gears due the the O/D having a one-way clutch in it's gear train.
In my opinion they were quite robust, mainly the Electrical side that caused problems (Go Figure!)



They do work in 2nd, 3rd, and 4th although it is not practical to use then in any thing except 4th. 1st gear is locked out. There is an anti reversing clutch to keep the overdrive from engaging in reverse. The factory manual says you need a special factory tool to assemble the anti reversing clutch but thats not true. I have dissembled and re assembled them many times with out the special tool. And most of the trouble with them will be electrical.

The problems with Lucas electrics is most people did not understand how it was set up and how it functioned.

Old joke...why do the English drink warm beer....they all have Lucas refrigerators....

 

[UncleS2]

My old Stupidbaker Lark V8 station wagon had 3-sp manual trans, plus a real, working, honest to goodness overdrive. It allowed that ragged old car to cruise easily at speeds of- let's just say way too fast for that car & tires!

While overdrive has now become so common it's taken for granted, that doesn't mean we should drop the term. It's a useful description, even when the seller of a vehicle says something like"drives good, good trans, o/d doesn't work though".

 

[XS650]

Originally Posted By: Stuart Hughes
My old Stupidbaker Lark V8 station wagon had 3-sp manual trans, plus a real, working, honest to goodness overdrive. It allowed that ragged old car to cruise easily at speeds of- let's just say way too fast for that car & tires!

While overdrive has now become so common it's taken for granted, that doesn't mean we should drop the term. It's a useful description, even when the seller of a vehicle says something like"drives good, good trans, o/d doesn't work though".

My 49 Ford with 3 on the tree had a BorgWarner overdrive, the same unit as your Lark IIRC it was designated an R10 with some letters and numbers after that to designate which case it had. There were several variations to mate with the different transmissions and drive shafts.

 

[mechtech2]

Most cars used to be rear wheel drive.
The transmission was in line - in series.
The top/high gear was straight through - 1 to 1.
An overdrive unit was sometimes added on the back, for better highway cruising efficiency.
This is how the tern came into general use.
Many transaxles and transmissions have an overdrive built in - top gear is about 0.8 to 1, not 1 to 1.
Dose the term overdrive have relevance anymore? We kinda know what someone means when they use the term, but it varies now. It needs details with it.

 

[XS650]

Originally Posted By: mechtech2
Most cars used to be rear wheel drive.
The transmission was in line - in series.
The top/high gear was straight through - 1 to 1.
An overdrive unit was sometimes added on the back, for better highway cruising efficiency.
This is how the tern came into general use.
Many transaxles and transmissions have an overdrive built in - top gear is about 0.8 to 1, not 1 to 1.
Dose the term overdrive have relevance anymore? We kinda know what someone means when they use the term, but it varies now. It needs details with it.


Back in the bad old days, it used to normally imply an add on gearbox. It's more cost and weight effective to build an overdrive ratio right into the transmission and virtually every new car transmission has overdrive tops gear(s) so the term as it was used is meaningless.