How effcient are current automatic transmissions

[dadof275103]

I have just read that the Chrysler 904 Torque Flite is one of the most effcient automatic transmissions in use. Is this true?

How is this tested?

Are automatics still 4% to 6% less effcient than a manuel transmission?

Michael
dadof275103

 

[pontiacjack]

"What goes around, comes around"...

I find it amusing that BrianPetersen posted "... NOWADAYS, it's a variable-displacement pump..." [re: automatic transmissions]. The original GM 4-speed Hydramatic first offered in 1939 (Cadillac, I think), and up through early 1956 (and even later in some trucks and Rolls Royces) all had a variable-displacement front pump. And they didn't need a lock-up clutch for cruising efficiency, as the fluid element (a 2-element coupling, not a torque converter) was out-of-the-circuit (just along for the ride) in 3rd and 4th gears.
I guess it's obvious that I'm a fan of the DualRange Hydramatic. I ran my first HydroStick (a DualRange modified for racing) back in '65. And I just recently built one for the pickup that I'm putting together.
Just for argument's sake, I'd love to work with a transmission-dynamometer shop on fixturing one of my HydroSticks to get some hard numbers on its efficiency.

 

[BrianPetersen]

It's interesting that auto tranny design went backwards before it went forwards again. I've heard of the early 4-speed automatics but know next to nothing about them. I think the Powerglide replaced them - 2 speeds with torque converter that was always in the circuit. 4-speed automatics didn't become popular again until the 1980's, nor did the capability of taking the fluid element out of the system during cruising.

 

[NormPeterson]

I think that early 4A may have been fitted into some 1957 cars. Briefly (and many years ago) I owned a 1957 Pontiac, might have been a Star Chief, and it had the 347 CID engine with a 4 barrel carb.

Anyway, I found out it had four forward gears once I swapped in a set of straight plugs and solid copper ignition wires. It was amazing how well the AM radio took up the task of being an auditory tachometer.


Norm

 

[pontiacjack]

Yes, Norm, your '57 Pontiac had a 4-speed Hydramatic. It was the 2nd-generation design called Dual-Coupling Hydramatic, first offered in mid-1956. It used a second, smaller fluid coupling to replace the front planetary clutch of the Dual-Range unit. The intent was to "soften" the 1-2 and 3-4 shifts- which it did- and thus wasn't useful as a modified race transmission (no way to instantaneously fill a coupling!). This secondary coupling remained in the circuit while cruising in 4th, so I'm sure it gave away some efficiency. I don't remember whether it retained the earlier variable-displacement pump.

 

[dicer]

Dual Range Hydramatic!

Yes 4 speed.
Yes vairable displacement pump.
Yes a lockup clutch
No Torque converter a fluid coupling instead.

Not sure how long offered in cars but I think they were still offered in trucks into the 60's.

The Dual coupling Hydramatic is a different transmission.