Allison question

[gojack]

I am unsure of how a torque converter works...
does it change your drive ratio's?

The Cummins powerspec.com site does not seem to list
the allison

I am looking at a pete 335 w/ MD3060P 5 speed with a .75 final drive ratio and a 4.88 rear end. The torque converter is a tc-413


What I do not understand:


TORQUE CONVERTER STALL TORQUE RATIO Kp-FACTOR* AT STALL

TC-413 2.44 85.4 (73.3)

Includes standard integral damper which is operational in lockup
*Kp-Factor defines torque converter capacity. Kp = the ratio of converter pump speed [rpm] divided by the square of pump torque [lb-ft (N·m)].

 

[Weave]

I don't know the math end of it. With a torque converter automatic, the torque conver's job (in basic sense) is to take the place of a standard clutch. But it actually does three things:
1. Allows the engine to idle at a standstill with the transmission in gear.
2. Allows the transmission to shift from gear to gear smoothly, without the engine's throttle being closed during shifts.
3. It multiplies engine torque increasingly as vehicle speed drops and throttle opening is increased.

The ratios to the input of the transmission vary greatly during torque converter operation. But with a lockup or lockout TC, when the vehicle reaches a certain speed, the TC locks into a direct 1:1 ratio between the engine and transmission input, and the losses from it are no longer there at that point.

With an Allison auto, they give you the proper torque converter for the engine and transmission combo. But as Doggie Daddy and I found out, some truck makers put rear drives on chassis that become expediter trucks that are geared for massive low end torque and will get terrible fuel mileage on the highway as they spin too much RPM at highway speed. The 4.88 rear on the Pete you are mentiong sounds right though for your combination to be fine for the highway.

-Weave-