From: Dan Hepner <emory!hposl03.cup.hp.com!dhepner>
X-Source: The Hotrod Mailing list
Date: Sep 1993
Subject: HD transmissions

> The T400 and the big Torqueflite should handle 800 ft-lb withouth much
>work.
>Posted by: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)

"Should handle" is subject to definition.  There's a big difference
between "it won't tear itself apart the first time you hit the pedal",
and "it will last 100k miles at this torque rate".  Neither of these 
transmissions would last 10k miles at an average torque of even 
400 ft-lb, but both should no doubt do 100k miles if they spent 
5 sec at 800 ft-lb and the rest of the time at 150 ft-lb.  Now
it might well be that the context "hotrod" supplies the
definition, and the definition has nothing to do with long
life; if so, fine. If that's not what everyone imagines, continue 
on.

Check out the failure modes of pickup automatics used for heavy
duty towing.  This towing doesn't increase the maximum torque, it
increases the average torque and the duration of periods at
high torque.  For some reasonable definitions, none of them, 
including the T400, can "handle" even 400 ft-lb (e.g. a truck 454),
not even close.  Medium duty trucks (3-5 "ton"), intended to be used
loaded much of their lives, frequently have very similar or
exactly the same engines that are available in pickups, about
400 ft-lb.  But they always have the heavier transmissions and 
rear-ends which can sustain actually _using_ that torque.

Dan Hepner

From: Dan Hepner <emory!hposl03.cup.hp.com!dhepner>
X-Source: The Hotrod Mailing list
Date: Sep 1993
Subject: HD transmissions
X-Sequence: 6363

>> Check out the failure modes of pickup automatics used for heavy
>> duty towing.  This towing doesn't increase the maximum torque, it
>> increases the average torque and the duration of periods at
>> high torque.  For some reasonable definitions, none of them, 
>> including the T400, can "handle" even 400 ft-lb (e.g. a truck 454),
>> not even close

>This is surprising as we were told by all the major players that an automatic
>was "stronger" and more "reliable" than a manual for towing and pulling.
>
>I opted for the 5 speed in my diesel ford pickup, as I have had much better
>luck with them than with auto.  The Ford 250 auto is rated higher gross than
>the manual, though in all the literature.....as was the dodge
>dave

Most people who tow prefer the automatic; as a sales technique, potential 
customers are reassured that the automatic is fine for this purpose. Ford
does indeed rate their auto higher than the standard, while Dodge rates 
their standard higher than the auto.

In the first order analysis however, they're all (auto, manual, GM, Dodge,
Ford) about the same. The fact that the GCWR are dependent upon
transmission demonstrate that the transmission is either the weak link,
or very nearly so. On a sustained basis, these transmission can handle 
about 150 ft-lb, with occasional bursts to 400 ft-lb, and last indefinitely.
This fits one common usage pattern of pickups fine.  Once you frequently 
offer them 400 ft-lb, their expected life begins to drop, and those who
tow 7-10k lb all the time know well that their transmission cannot be 
expected to last 100k miles.  This is tolerated by consumers as "handling 
it", but this reliability would not be tolerated by commercial users, who 
use significantly stronger components behind similar engines (as well as 
larger brakes, frames, etc).  They pay a lot more up front, get less fuel
mileage, and in many places, pay a lot more for license and insurance as well.

Dan Hepner (Dodge Cummins, 5-spd, no trailer)