Torqueflight trivia

[flyinlow]

Why does the the pressure in the transmission have to be so much higher in reverse?

[Nacho-RT74]

Torqueflite... although I think you can flight with torque

dunno about the question

[68X426]

  Lower gear ratio?

[lisiecki1]

"borrowed" from the internet....if we are playing an actual game I apologize for cheating 

Hydraulically, there are also a couple of interesting things to note. Governor pressure will not be used in reverse and a quick line pressure check shows reverse to have about 250 + or - 20 psi (where normal line pressure is 75+ or - 19 psi). This is not immediately obvious why reverse should be so high until the rear clutch and front clutch are compared.

The rear clutch is on in all forward gears. It uses a Bellevifle spring washer to multiply the piston apply force the necessary amount to transmit engine torque through the rear clutch pack. However, the front clutch has no multiplication factor to depend on when it is applied. Since direct drive is the only other time the front clutch is used and the vehicle is already in motion, no extra holding power is needed to sufficiently lock the front clutch drum. But going into reverse, the vehicle is stationary, and much greater torque (2.2 times as much) will be transmitted through the front clutch plates. Therefore, through a couple of hydraulic tricks, line pressure is almost tripled to give the front clutch the necessary holding power.

[68X426]

I just got schooled.

[John_Kunkel]

I can't say, for sure, why the line pressure is higher in Reverse but the explanation provided by lisiecki1  doesn't make sense.

First off it contends that the lack of front clutch apply power is the reason for the higher pressure, this is nonsense. While the rear clutch does get added clamping power from the leverage advantage of the Belleville the rear clutch piston is much smaller in diameter than the front clutch piston. Anybody who knows anything about hydraulics knows that piston diameter is everything....the larger the diameter of the piston, the more square inches of area are exposed to hydraulic pressure and, therefore, the greater the force exerted by the piston. Without doing a lot of math it's safe to say that the front clutch has equal or more clamping power than the rear does.

Second, it contends that the 2.2 Reverse ratio needs more clamping power from the front clutch than the rear clutch needs for the 2.45 first gear ratio. This, too, is kinda iffy because there is only about 10% difference and the vehicle is seldom accelerated at full throttle in Reverse.

So why the higher pressure in Reverse? Look at the size of the rear band compared to the front, the rear band must hold much tighter in Reverse because it stands alone unlike the only other time the rear band is applied and that is in manual 1st...in manual 1st the rear band is aided by the sprag so less holding power is required. Also, there is no throttle pressure in Reverse so the amount of pressure to the clutch/band isn't increased with added throttle, so it makes sense to provide a consistant high pressure for maximum holding power no matter what the throttle setting.

Just my opinion.

[lisiecki1]

this is the entire quote that I found on allpar, maybe it will make some more sense in it's entirety.......

Reverse Gear

When the Torqueflite is shifted into reverse a couple of interesting things happen. First the rear clutch, used in all forward gears, is deactivated. Then the front clutch is applied which locks on to the front clutch hub-input shaft assembly. Along with application of the front clutch, fluid is directed to the low-reverse servo which locks the low-reverse band tightly around the low-reverse drum-rear planet carrier assembly. Engine torque can now be transferred through the transmission.

Looking at this in order, it happens like this:

The front clutch is applied transferring engine torque through the sun gear driving shell, driving the sun gear in the same direction as the engine. With the low-reverse band holding the rear planet carrier stationary, torque is transmitted only through the planet pinions (via the sun gear) driving them in a reverse direction. The only thing left to spin is the rear annulus gear which is splined to the output shaft. Using this planetary only gives one turn to the output shaft for every 2.2 turns of the input shaft, again remembering the output rotates the opposite direction of the input shaft.
Hydraulically, there are also a couple of interesting things to note. Governor pressure will not be used in reverse and a quick line pressure check shows reverse to have about 250 + or - 20 psi (where normal line pressure is 75+ or - 19 psi). This is not immediately obvious why reverse should be so high until the rear clutch and front clutch are compared.

The rear clutch is on in all forward gears. It uses a Bellevifle spring washer to multiply the piston apply force the necessary amount to transmit engine torque through the rear clutch pack. However, the front clutch has no multiplication factor to depend on when it is applied. Since direct drive is the only other time the front clutch is used and the vehicle is already in motion, no extra holding power is needed to sufficiently lock the front clutch drum. But going into reverse, the vehicle is stationary, and much greater torque (2.2 times as much) will be transmitted through the front clutch plates. Therefore, through a couple of hydraulic tricks, line pressure is almost tripled to give the front clutch the necessary holding power.

and the link:

http://www.allpar.com/mopar/transmissions/torqueflite-tom-hand.html

[Challenger340]

Why does the the pressure in the transmission have to be so much higher in reverse?

Long Story Short ?
It's Because the Helical Cut Gears in the Planetaries are designed to reduce Noise & "Friction" going "Forward", hence, require additional Fluid Pressure to hold the Clutchs against the Increased Friction when forcing them "Backwards".

See for yourself,
Trace the Power Line in a Planetary re "Driven over Drive" in Forward,
then,
FORCING it to go backwards.

1st and Reverse in 904 is the same gears/same ratio.

[flyinlow]

 


No burnouts in reverse for me.

Thanks , Still learning after all these years......Craig

[RD]

did someone say reverse burnout?  go to 44 seconds into the video MUHAHAHAHHAHA!!!!

http://www.youtube.com/watch?v=CHVg0O6b9l0

[flyinlow]

When I was 16 I was driving my Fathers 64 Plymouth slant six with a 3 in the tree. Leaving a buddys house I dicided to burnout in reverse. Broke the reverse gear. Told  Dad my foot slipped off the clutch backing up a hill....RIGHT

[troy.70R/T]

Very interesting.