Why automatic transmissions have less gears?

[Elkins45]

Originally Posted by 69GTX
2 speed GM Power Glide (1950-1973).


My dad's 67 Impala had a 327 and a Power Glide. PRNDL. Manual steering and brakes, no AC, black paint and black vinyl seats. In the summer you could cook hot dogs on the rear deck. You better have your foot hard on the brake when you drop it in gear or it will pop you forward a couple of feet.

I think that car is still running somewhere. He sold it to a neighbor of his brother who restored it. I would love to see that old beast again.

 

[clinebarger]

Originally Posted by Dinoburner
Iconic drag racing trans esp cast iron case.



I can't recall ever building a Cast Iron "Glide" for drag racing. Two Speed competition prepped TH400's are quickly replacing the Aluminum "Glide" as the trans of choice in higher HP drag cars.

 

[RayCJ]

Originally Posted by atikovi
Are these 8,9, and 10 speed transmissions as durable as the older versions? Don't the gears have to be smaller or narrower to fit in the same space as they did before?


I know that Mazda's 6 speed autos are doing very well. They've been around for a while and have a great track record.

If you read about "planetary gears", you'll see that it's the ratio of the sizes and not the actual size that determines the gearing. The overall size of the transmission and how hefty the gears must be, is determined by how much horsepower the unit is rated for.

Ray

 

[Cujet]

Originally Posted by mattd
The 6R140's rear gearset uses 2 different size sun gears within the same assembly with 8 planets. It's about 400$ for the entire gearset from ford. That's how this transmission achieves 6 forward ratios with only 2 actual gearsets (forward planet set has only 1 sun gear with 4 small planets)

 

[Cujet]

Originally Posted by atikovi
Are these 8,9, and 10 speed transmissions as durable as the older versions? Don't the gears have to be smaller or narrower to fit in the same space as they did before?


I'd guess yes, as modern turbocharged engines make a lot more torque than conventional engines. In the end, torque load is the limiting factor in transmission design.

We move 1500HP through a 1 inch driveshaft in the aviation world via high RPM and low torque.

 

[JTK]

The start and end ratios haven't changed, just the method of getting there has. CVT have an infinite number of ratios going from low to high.

 

[supton]

Originally Posted by Cujet
Originally Posted by atikovi
Are these 8,9, and 10 speed transmissions as durable as the older versions? Don't the gears have to be smaller or narrower to fit in the same space as they did before?


I'd guess yes, as modern turbocharged engines make a lot more torque than conventional engines. In the end, torque load is the limiting factor in transmission design.

We move 1500HP through a 1 inch driveshaft in the aviation world via high RPM and low torque.

Seems like we've all worried about that, yet, 6+ speed autos have been around for more than a decade. And we're not hip deep in dead transmissions. Anything can wear out, but they don't seem any worse than their predecessors.

IMO part of it is better integration between engine and trans. ECU tells the TCU "I wanna shift" and then lets off torque momentarily. Transmission can then shift when not under load. Furthermore torque management can be used to limit total engine torque (important in first and second gear to prevent damage not just to transmission but other driveline parts).

 

[atikovi]

So an 8,9 or 10 speed doesn't have 8,9 or 10 gears?

 

[4WD]

Originally Posted by 69GTX
2 speed GM Power Glide (1950-1973).


BiL's goat would chirp ‘em at 70 mph during that single shift …

 

[Trav]

Originally Posted by Dinoburner
Iconic drag racing trans esp cast iron case.


The only iron case I remember seeing was the Ford-O-Matic and possibly an early Chrysler dual pump unit (front and rear pumps, you could push start these) but I don't remember much about them, they were before even my time. There may well have been an iron case Power Glide in the very early 50's after a transmission plant burned down but again before my time.

 

[clinebarger]

Originally Posted by Trav
Originally Posted by Dinoburner
Iconic drag racing trans esp cast iron case.


The only iron case I remember seeing was the Ford-O-Matic and possibly an early Chrysler dual pump unit (front and rear pumps, you could push start these) but I don't remember much about them, they were before even my time. There may well have been an iron case Power Glide in the very early 50's after a transmission plant burned down but again before my time.



The last year for the Iron Powerglide was 1962, They also had a rear pump! Before my time as well.....But I've built a few for restorations.

 

[clinebarger]

Originally Posted by 4WD
Originally Posted by 69GTX
2 speed GM Power Glide (1950-1973).


BiL's goat would chirp ‘em at 70 mph during that single shift …


Pontiac rarely used the Powerglide.....As is was designed & built by the Chevrolet Division. Pontiac used the Super Turbine 300 2 speed automatic.

 

[Dinoburner]

The powerglide in my first car was cast iron. The 105 horsepower going into it did not stress it much. As to cast iron cases being used by drag racers, I have no personal experience just anecdotal in reading many hotrod type magazines

 

[SeaJay]

Seems to be an arms race on automatics these days to get as many gears as possible without going to a CVS. More gears, more expense for a dwindling improvement in MPG and performance with the extra gears.

Not so many folks wanting a manual transmission these days, the ones that do are just happy to find that option in their ride. IMO, anything more that 5 forward gears in a manual transmission is just too darn much rowing up and down. Except for high performance vehicles, 4 forward gears works just as well as 5 with the benefit of less rowing.

 

[Quattro Pete]

Originally Posted by SeaJay
Seems to be an arms race on automatics these days to get as many gears as possible without going to a CVS.

But going to Walgreens is still OK.

 

[meep]

Originally Posted by Trav
Originally Posted by Dinoburner
Iconic drag racing trans esp cast iron case.


The only iron case I remember seeing was the Ford-O-Matic and possibly an early Chrysler dual pump unit (front and rear pumps, you could push start these) but I don't remember much about them, they were before even my time. There may well have been an iron case Power Glide in the very early 50's after a transmission plant burned down but again before my time.



had a '57 bel air, its PG was dual pump and iron cased. Yes, you could roll start it, but it needed about 25mph to get enough rpm to crank the wet-plugged 283 in front of it. it was eerie to roll start because you couldn't tell the engine was turning over. Push starting a manual, you knew it because you'd feel it as dropping the clutch and feeling the engine "lump." In the PG, you rolled in N, pushed it down 2 (PNDLR) into L and it'd gently build pressure, spin the TC, and somehow in all that mess of hydraulic squish the engine would supposedly turn. You'd either make it to the bottom of the hill with it quiet, or with it running. Strangely enough, on our hill, 9 times out of the 10 it was running. It was almost more effective for a reliable start than using the starter. Maybe a higher rpm. But it was still eerie, because there was no sound, no vibration, no indicator of what was happening. Maybe the oil light went off half way down, but rather than watching the light we were watching the road. With a Stop sign and 'T' intersection at the bottom, you had to also remember to prioritize on being able to stop before the end, over getting it fired up. It was a lot of car to stop on a downhill slope, with manual drum brakes, 1950s steering, skinny tires, and crude suspension.

 

[supton]

Originally Posted by Quattro Pete
Originally Posted by SeaJay
Seems to be an arms race on automatics these days to get as many gears as possible without going to a CVS.

But going to Walgreens is still OK.

Won't be long before your typical transmission comes with more gears than your prescription bottle comes with pills!

 

[clinebarger]

Originally Posted by Cujet
Originally Posted by mattd
The 6R140's rear gearset uses 2 different size sun gears within the same assembly with 8 planets. It's about 400$ for the entire gearset from ford. That's how this transmission achieves 6 forward ratios with only 2 actual gearsets (forward planet set has only 1 sun gear with 4 small planets)

The Powerglide was the first mass produced transmission to use a Ravigneaux planetary gearset IIRC, The Super Turbine 300, Ford FMX, & the GM 3L30/4L30E also used them.

The Simpson style gearset was far more popular for the longest time, Now everyone except Honda uses them now.....What's Old is New again!!

 

[i6pwr]

Originally Posted by 69GTX
2 speed GM Power Glide (1950-1973).



Yessir.....2 speeds is plenty...

fun starts at 1:00