Why were overdrives put into cars?

[lspencer534]

The were popular in the 1950's, maybe other times as far as I know. Let’s think for a minute why overdrives were put in cars in the first place. I mean after all, anyone can put in a 5th gear on a transmission, why an overdrive? (I personally think a guy named Rube Goldberg had a major part in their design).

It was added as an option on most cars in order to reduce engine RPM (and consequently wear) on the highway and increase fuel mileage. Secondarily it was also used to increase the number of speeds forward, giving a better selection of gear ratios for driving. Still, a 5th gear accomplish this.

:confused5:

[MrPeabody]

The were popular in the 1950's, maybe other times as far as I know. Let’s think for a minute why overdrives were put in cars in the first place. I mean after all, anyone can put in a 5th gear on a transmission, why an overdrive? (I personally think a guy named Rube Goldberg had a major part in their design).

It was added as an option on most cars in order to reduce engine RPM (and consequently wear) on the highway and increase fuel mileage. Secondarily it was also used to increase the number of speeds forward, giving a better selection of gear ratios for driving. Still, a 5th gears accomplish this.

:confused5:

Maybe because it was an add-on to existing transmissions which may have been stockpiled in inventory because back then the transmission was a part of the car that was used unchanged for many years.

I don't know if it's true or not but I had a old uncle who used to say the reason American car manufacturers resisted disc brakes for so long was because they had millions of brake drums in inventory.

[Kerrmudgeon]

My old man's 36 Lafayette had an overdrive in it. It was called the "free wheeling" option. When you only had 3 speed trannies it made sense to have an OD on the highway.

Gas was all of what .30$ a gallon? :)

[mrvette]

It all depends on the tire diameter, rear ratio, size of engine and fuel economy....and of course vehicle weight.....slight input from aerodynamics....

so to keep engine wear and fuel consumption down, especially on flat lands, and keep the possible acceleration in traffic to acceptable levels, there had to be more gears....now to reduce the rear ratio down to say 2.73 with a turbo 400, with a 2.5 first gear, 1.6? second and 1.0 third is just fine with a 455 inch engine and 550 ft lbs at idle,.....especially in a 4100 lbs Goat.....

but you gotta know you not going 100 mph for longer than a mile at best....

now out in Florida where my 336 ratio '72 vette is cruising at 80 on the freeways, I needed an o/d trans the muncie was shifted from second to forth most of the time anyway, not much for hills in Florida....so I got lazy but cruising at 4 grand for miles on end is a tad tough on a 350 engine, so I put in the cheapest OD I could afford.....back in '97, it's a 200 4r today.....and so cruise at 2400 rpm at 80 mph......and gain some MPG in the deal....

:seasix:

[Burro (He/Haw)]

now to reduce the rear ratio down to say 2.73 with a turbo 400, with a 2.5 first gear, 1.6? second and 1.0 third is just fine with a 455 inch engine and 550 ft lbs at idle,.....especially in a 4100 lbs Goat.....
What'd he just say?

[lspencer534]

What'd he just say?

He installed a flux capacitor.

[Burro (He/Haw)]

He installed a flux capacitor.

In a Goat? Does PITA know about this?

[lspencer534]

My old man's 36 Lafayette had an overdrive in it. It was called the "free wheeling" option. When you only had 3 speed trannies it made sense to have an OD on the highway.

Gas was all of what .30$ a gallon? :)

Gas was $0.30 a gallon well into the 1960's.

[mrvette]

What'd he just say?

HEY!!!! my goat got published.....Feb '95 issue of High Performance Pontiac ....called Injected Madness.....I built it over winter 91-92 in my garage, with some help from TIG welder shops.....still have that highly modified induction....

and if you dunno what a GOAT is, well, you just wet behind the ears, kid.....


:lol:

[Kerrmudgeon]

Gas was $0.30 a gallon well into the 1960's.

I pumped gas in the early 70s after school and I remember it being .39.9 for a long time and some times gas wars down to .34.0!....those were the days. :seasix:

[lspencer534]

I pumped gas in the early 70s after school and I remember it being .39.9 for a long time and some times gas wars down to .34.0!....those were the days. :seasix:

I remember it well. I even remember when a pack of cigarettes cost more than a gallon of gasoline at 24 cents a pack. Regular and premium were only 4 cents apart. Two dollars got you eight gallons of gasoline, abut half a tank.

[simpleman68]

What'd he just say?

Let me see if I can be of assistance. :D
Scott


now to reduce the rear ratio down to say 2.73
Ratio of the rear differential in that it rotates 2.73 revolutions for one rotation of the axle.

with a turbo 400
GM THD400 transmission (turbo hydramatic)

with a 2.5 first gear, 1.6? second and 1.0 third is just fine
Ratio of each transmission gear to rotation of the engine. 1st gear would translate 2.5 rotations of the engine to one turn of the output shaft of the trans.


with a 455 inch engine and 550 ft lbs at idle,.....
455 cubic inch displacement that no way in hell made 550 lb ft at idle although hp/tq specs were rated at the block with all accessories removed in a cold, oxygen rich lab. Post '72 or so more accurate numbers were used. "Net HP vs Gross"

especially in a 4100 lbs Goat....
1970 GTO weighed 3641 (hardtop) and 3691 (vert) had to look that one up.

[Steve Austin]

In those days less shifting was thought of as better. Automatics were not perfected so it was a luxury thing if you had a 2 speed instead of a 3 speed. Having the option to shift more was not considered that good.

[Burro (He/Haw)]

Let me see if I can be of assistance. :D
Scott


now to reduce the rear ratio down to say 2.73
Ratio of the rear differential in that it rotates 2.73 revolutions for one rotation of the axle.

with a turbo 400
GM THD400 transmission (turbo hydramatic)

with a 2.5 first gear, 1.6? second and 1.0 third is just fine
Ratio of each transmission gear to rotation of the engine. 1st gear would translate 2.5 rotations of the engine to one turn of the output shaft of the trans.


with a 455 inch engine and 550 ft lbs at idle,.....
455 cubic inch displacement that no way in hell made 550 lb ft at idle although hp/tq specs were rated at the block with all accessories removed in a cold, oxygen rich lab. Post '72 or so more accurate numbers were used. "Net HP vs Gross"

especially in a 4100 lbs Goat....
1970 GTO weighed 3641 (hardtop) and 3691 (vert) had to look that one up.
What the,,,,,,,

:rofl::rofl::rofl:

[markids77]

100 MPH was considered a grail at the time for a production automobile. Since no one had yet invented the 5 or 6 speed transmission; an overdrive unit piggy backed to the factory three speed made sense as a "performance" option. "The Ton" was a big deal in the public's perception of performance capability so manufacturers found the least expensive, most direct method of providing that.

[NeedSpeed]

Overdrive vs another gear was probably advertising.

[simpleman68]

What the,,,,,,,

:rofl::rofl::rofl:

Too boring? I speak "Gene" :Jeff '79:

Scott

[island14]

What the,,,,,,,

:rofl::rofl::rofl:

Obviously Scott is an educated man.


He took "Gene Speak" for extra class credits in college... :lol:


Doc Holiday and Johnny Ringo Latin Translated (What they really said) Tombstone Movie - YouTube

[island14]

I pumped gas in the early 70s after school and I remember it being .39.9 for a long time and some times gas wars down to .34.0!....those were the days. :seasix:

Same here.. Started pumping gas about 72 or 73, and it was between 34 to 36 cents a gallon.

About 4 of us could all chip in our lunch moneys and buy enough gas to drive around about all day, and that was even with a 369 SS Nova a buddy of mine had.

[island14]

I remember it well. I even remember when a pack of cigarettes cost more than a gallon of gasoline at 24 cents a pack. Regular and premium were only 4 cents apart. Two dollars got you eight gallons of gasoline, abut half a tank.

The local brand of smokes was still about a quarter till they started the Sin Tax last year, but still under 50 cents a pack here now.

Marlboros are more expensive at about $10 a carton.

[Aerovette]

I am pretty sure that a 5th gear, or 6th, or 15th gear becomes irrelevant once you hit a 1 to 1 relationship of engine and output shaft. Overdrive changes the ratio to one that allows the engine speed to drop but the output shaft speed to remain.


...or I am dead wrong. :D

[island14]

Do you have something with Overdrive on it, or plan to install on something Spence?

I have the old Borg Warner overdrive manuals if needed.

[RED-85-Z51]

I think often people mistake "an extra gear" as overdrive.

Overdrive is when the output shaft is turning faster than the input shaft.

In other words at 2000 rpms, in a truck with a 4L60E, in Drive (3rd gear), the engine is turning 2000, and the output shaft it turning 2000. 3rd is 1:1, no reduction, no overdrive.

In OD (4th), the input is still spinning the same 2000 as the engine, but the output is turning faster than 2000, something like 2300....

This allows the engine ti go down in speed, where torque is plentiful, and fuel is sipped....and also allows a higher top speed.

You can have an 8 speed...and as long as 8th gear is 1:1....you have no overdrive. You can even have 2 overdrives, where the top 2 gears are both overdriven....Say 81/100 and 66/100....

[island14]

Dunno why, but every time I hear overdrive I think about this song...

https://www.youtube.com/watch?v=3R7l7nDuj1o

[Aerovette]

I think often people mistake "an extra gear" as overdrive.

Overdrive is when the output shaft is turning faster than the input shaft.

In other words at 2000 rpms, in a truck with a 4L60E, in Drive (3rd gear), the engine is turning 2000, and the output shaft it turning 2000. 3rd is 1:1, no reduction, no overdrive.

In OD (4th), the input is still spinning the same 2000 as the engine, but the output is turning faster than 2000, something like 2300....

This allows the engine ti go down in speed, where torque is plentiful, and fuel is sipped....and also allows a higher top speed.

You can have an 8 speed...and as long as 8th gear is 1:1....you have no overdrive. You can even have 2 overdrives, where the top 2 gears are both overdriven....Say 81/100 and 66/100....


Ok, I guess it sounds better when YOU say it. :shrug:

:D