Transmission grenade theory

[Randy Bishop]

You know the story - just happened to us. Six hours from home, the tranny
in our 2000 GV self destructed coming off the interstate. Took it to an
indepenent ATRA shop & opted for a bench rebuild. Failure sequence appears
to be : Torque converter > pump > everything else. Cost with an 18/18
nationwide warranty - $2400. Tranny was serviced at severe duty service
interval. (73,000 on tranny at failure). Our 89 Caravan suffered a similar
failure at about the same point in its life

Thinking about this experience led me to this idea which I would like to
discuss.

DC uses the same tranny across a broad product line, in vehicles with wide
ranging GVWR. In the lighter cars with limited seating and hauling
capabilities, the tranny will hold up for the life of the vehicle. In the
minivans, the loads are much higher and put more stress on the tranny,
resulting in a shorter life.

After two experiences, I think if I purchase another van, I will go full
size with conventional layout.

Has anyone done any research on vehicle size/weight vs. tranny failure
rate?

Randy

 

[Ted Mittelstaedt]

You know the story - just happened to us. Six hours from home, the tranny
in our 2000 GV self destructed coming off the interstate. Took it to an
indepenent ATRA shop & opted for a bench rebuild. Failure sequence appears
to be : Torque converter > pump > everything else. Cost with an 18/18
nationwide warranty - $2400. Tranny was serviced at severe duty service
interval. (73,000 on tranny at failure). Our 89 Caravan suffered a similar
failure at about the same point in its life

Thinking about this experience led me to this idea which I would like to
discuss.

DC uses the same tranny across a broad product line, in vehicles with wide
ranging GVWR. In the lighter cars with limited seating and hauling
capabilities, the tranny will hold up for the life of the vehicle. In the
minivans, the loads are much higher and put more stress on the tranny,
resulting in a shorter life.

After two experiences, I think if I purchase another van, I will go full
size with conventional layout.

Has anyone done any research on vehicle size/weight vs. tranny failure
rate?

I don't think that you could, for two reasons:

1) The 41TE/A604 has gone through so many revisions that you can't get an
apples-to-apples comparison.

2) By the time you hit 70K+ miles, how the car was being driven is more of
an impact.

Consider this. The stress presented to the tranny is a ratio of
accelleration to inertia. In
short, a 2000pound vehicle accellerated at, say 1m/sec presents the same
stress on the
tranny as a 1000pound vehicle accellerated at, say 2m/sec

Now, granted if you feather-foot a heavy vehicle in order to keep the strain
down
to the same level as normal driving a light vehicle, the upshot is that the
strain placed
on the tranny for the heavier vehicle simply lasts longer in order to get
both vehicles
up to the same speed. So another way of saying it is that you can choose to
have
a lot of strain on the tranny for a short period, or a little strain on the
tranny for a
longer period, irregardless of vehicle weight, just by adjusting your
driving, but in
the last analysis, the tranny that is hauling the heavier vehicle does more
work.

BUT, the crucial thing that I have observed about mechanical systems, is
that WEAR
seems to be directly related to the strain placed on the device. In short,
a tranny that is under high
strain for a short period of time wears a lot faster than a tranny that is
placed under
low strain for longer periods, even if both trannies do the same work.

So to put it in laymans terms and relate it to your problem, the A604/41TE
may be
perfectly adequate tranny for even heavier vehicles, depending on who is
driving and
how they are driving. So I don't think that a study is going to show any
difference unless
it takes into account the driving style of how the vehicle is driven.

And one last thing to throw on the fire - heat TREMENDOUSLY accelerates
wear. I suspect that a huge number of early transmission failures could
have been
avoided simply by the factory plumbing in a decent transmission cooler
instead of
circulating it through a heat exchanger in the radiator. While you need
some heat in the
trans fluid for correct viscosity, it would be interesting to see the long
term results
of a trans where the fluid was maintained at 90 degrees instead of 120-150.

Ted

 

[Bill Putney]

...Consider this. The stress presented to the tranny is a ratio of
accelleration to inertia...

You meant to say the *product* of acceleration and inertia - work the
numbers (ratio vs. product) in your example that follows and you'll se
what I mean. Obviously as either acceleration *or* inertia go up, so
does stress on the tranny.

...In short, a 2000pound vehicle accellerated at, say 1m/sec presents > the same stress on the
tranny as a 1000pound vehicle accellerated at, say 2m/sec...

Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")

 

[Brayton]

Would the size of the transmission cooler be dependent on the climate
that the car is used in? For example, where I live, the absolute 'blow-your
mind' high temperature would be 80°F, and in the worst of the winter, it
could get down to -40°F at the worst. Wouldn't the factory cooling solution
be sufficient in the winter time here, yet a factory option overkill at the
same time? (Winter lasts about 4 to 5 months here.) I would suspect that
in some cars, it's possible to be too cool. Yes no?

 

[Ted Mittelstaedt]

You meant to say the *product* of acceleration and inertia - work the
numbers (ratio vs. product) in your example that follows and you'll se
what I mean. Obviously as either acceleration *or* inertia go up, so
does stress on the tranny.

Your exactly right, I muffed that one. I also muffed another one when I
said that wear was proportional to stress, it's not, it's a logrithmic
function. In short, as stress increases at a steady rate, my experience
is that wear increases at a much more rapid rate.


Ted

 

[Ted Mittelstaedt]

Would the size of the transmission cooler be dependent on the climate
that the car is used in? For example, where I live, the absolute 'blow-your
mind' high temperature would be 80°F, and in the worst of the winter, it
could get down to -40°F at the worst. Wouldn't the factory cooling solution
be sufficient in the winter time here, yet a factory option overkill at the
same time? (Winter lasts about 4 to 5 months here.) I would suspect that
in some cars, it's possible to be too cool. Yes no?

Yes. In fact, many semitrucks have zippered covers over the grill of the
truck, you will see in wet and cold weather many of them will zip them up
to cover half the radiator, else the cooling from the radiator is too great.

With autos, you do avoid some of that because most cars now have
thermostatically controlled electric cooling fans, and of course the engine
thermostat in the radiator will shut the coolant flow down if the coolant
gets
too cold. It wouldn't take much to rig an electronic (or mechanical) bypass
valve on the tranny hydraulic lines to perform a similar function.

Ted

 

[Ivo]

I also muffed another one when I
said that wear was proportional to stress, it's not, it's a logrithmic
function. In short, as stress increases at a steady rate, my experience
is that wear increases at a much more rapid rate.


Ted

Ted,
Then it's quite the opposite of logarithmic, namely it is exponential.

Cheers,
IK

 

[Randy Bishop]

Perhaps in relation to the style of driving, the terrain the vehicle runs
in has an effect on tranny longevity. Here in Upstate New York Finger
lakes region we have a combination of steep hills and high speeds which
would also dovetail with the excessive heat shortening tranny life points
you made. I think the aux cooling idea is sound and I will put in a cooler
with this rebuild.

Any recommendations for a cooler in a high stress application for these
trannys?

Randy