Most of the trannys in Dodge trucks are based on the old 727/904 design,
which held up quite well behind 440s and 426 Hemis. The exception is the
tranny behind the 4.7L engine (the tranny with two 2nd gears); this tranny,
IIRC, is based off of the A604 FWD tranny.
As for the others, there are two items that weaken them from their 727/904
ancestors. The first item is that on many models, the Low-Reverse band
application has been slowed to soften shifts for the soccer moms and yuppies
who are now driving these trucks. The slowed application does indeed make
for softer shifts, but also greatly increases wear on this band, possibly
leading to pre-mature failure, especially if you use L-R a lot, such as when
using a snowplow. Most tranny kits will fix this problem, leading to hard
shifts, but a much stronger tranny.
The second weakness in the tranny is the OD unit. It was added almost as an
afterthought to the tranny, and only receives a portion of the lubrication
that runs through the main tranny. This poor lubrication allows excess heat
to build up in the OD unit, particularly when the tranny is "hunting" gears,
shifting in and out of OD (such as when towing or driving in the mountains).
The fix is to either 1) increase lubrication to the OD unit (a good tranny
mechanic should be able to do this) and make sure the tranny is receiving
maximum cooling (helps to have extra tranny cooler and install a temp gauge
in the tranny fluid line), or 2) don't use OD, especially when towing,
driving in hills and putt-putting around town.
The above weaknesses pertain to gasoline engines. A third cause of failures
is not really the fault of the transmission itself, but rather that it is
used in an application for which it was never designed for - I'm speaking of
putting the tranny behind a diesel engine (i.e. - Cummins). The tremendous
off-idle torque generated by the Cummins is hard on the tranny. Even
moreso, the tremendous low-rpm torque of the Cummins allows the tranny to
operate in OD without "hunting" gears like it would with a gasoline engine.
This sounds good, but remember that the OD unit's lubrication is dependent
on rpms. If that diesel/tranny combination is pulling heavy loads in OD at
low rpm, we're talking *very little* lubrication and lots of heat, a recipe
for tranny failure. Again, the solution is simple, don't use OD when the
vehicle is under load. This is also a problem on Fords (yes, they have a
number of tranny failures behind their diesels, also). Chevy hasn't had a
problem because they don't have a hi-po diesel - this will change when they
introduce their (Isuzu) DuraMax next year, but it will have the commercial
Allison auto tranny behind it (strong tranny, but VERY big and heavy = not
good for mpg).
It also helps to change the tranny fluid and filter every 30k. I've done
this on my truck (do it myself, don't trust most tranny shops), and I've
over 150k on my tranny and it still shifts like new. I also let the truck
warm up in neutral (tranny won't pump fluid in Park). If you have a choice,
park your truck so that when you start it in the morning, you can just take
off going forward without having to put it in reverse. Sounds like a
hassle, but if you make it a habit, you won't even realize you're doing it
after a while.....
-- '92 Dak CC 2wd 318 3.55 A-518 '84 GoldWing Interstate
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