A604 Question...

OK, so we have talked considerably about various aspects of the 4
Speed Automatic A604. Not so long ago, I mentioned about travelling
through the mountains, and I had made a comment about the transmission
and using the transmission as a break based on my experiences with
other transmissions, and someone here called me to task with the
statement "Haven't you read your manual??"

Well, no I had not. I did receive the owners manual with the 94 Grand
Caravan I purchased, but had not really looked at it.

SO I did! I am still confused. All my manual talks about is towing,
and it is explicit - when towing, you "MUST" have the transaxle in "D"
to prevent overheating???

This is the opposite of what I would have expected. So I will recap...

I have the 7 passenger capacity, and - while I will be fully loaded -
I will NOT be towing anything. I will, however, be travelling through
the rockies.

Am I correct then, that the best option is to simply leave the trans
in "D" as opposed to "3"?

And would someone please either explain the theory of operation of
this tranmission, or point me to a link that does??? I really like to
know how things work under the hood, even if only on a cursory basis.
The A604 seems to be quite a departure from anything that came before
it, and I would like to understand what is going on (especially in
comparison to older transmissions).

Thanks!

 

The best option for your 94 GC if your doing ANYTHING more
serious than shuttling no more than some children with a total
combined weight of under 200 pounds, plus your own weight,
at speeds under 45Mph in the city, is to install an additional
transmission cooler.

Go to a wrecker and look for a Caravan with a trailer hitch
on it, 10-to-1 it will have an external, additional trans cooler.
in many cases you can find the factory original additional
trans cooler. (it was part of the optional Mopar towing
package) Take the cooler and all the plumbing, then go
to a TRUSTED transmission shop and have them flush
out the cooler and install it DOWNSTREAM (ie: as a post-cooler)
of the in-radiator factory cooler.

Purchase one of the ATSG transmission rebuiild manuals for
this transmission.

Ted

 

I am certainly not an expert on this, but if my understanding is
correct, the difference between 'D' and '3' is that 'D' allows the
torque converter clutch to lock the torque converter for direct drive
(3rd gear) and 4th gear (OD) - that means no slipping under load in 3rd
and 4th gear. '3' locks out the clutch lock, and therefore allows
slippage, especially under heavy load, and also locks out going into 4th
gear (OD).

Any slippage by definition creates potentially damaging heat, and the
amount of heat generated in '3' with no torque converter lock on a long
upgrade with load would be tremendous. I wouldn't think that the amount
of heat on the down slope would be that much being that the engine
braking torque is nowhere near it's WOT torque. The tradeoff of saving
the brakes might be worthwhile. Too bad they don't have an OD lockout
switch that would allow locking out 4th gear but still lock the torque
converter.

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

 

Also, the FSM explains the theory of operation. You can find them in
pdf format on the internet - at least for the LH cars (42LE). An
Alldata subscription on the vehicle would probably contain that section
out of the FSM, but I haven't checked.

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

 

I'm not sure that selecting "3" completely prevents TCC lockup, but in
general I think you're right in that the TCC lockup "schedule" in "3"
allows a lot more slippage than just putting it in "D" and letting it do
what it needs to do. I have observed (via the tach) that when climbing a
long grade in "D" but with the computer having placed the transmission
in 3rd gear, there comes a point where the computer seems to decide,
"Well, I'm not going to be able to shift to 4th ANY time soon, so I'd
better lock the TCC all the way" and it does. I haven't observed such
behavior when I've picked "3" manually.

People need to remember that the 41TE/42LE are NOT designed with towing
in mind like a 46RH is, and ARE designed to optimize everything they
need to optimize when the selector is just left in "D". I only use "3"
for engine braking when going DOWN grades with my 42LE equipped car.

 

So what is the "OD" switch on the dash for then??? I for get what it
says exactly, but I thought is was something like "OD OFF". It is in
the same cluster as the rear wiper switch and rear window defroster.

 

Was the 46RH an option for the GC? Can you bolt one in if you wanted
to?

 

Is this in a Chrysler minivan? What year?

I'm familiar with that switch in the Ram trucks and full-size vans with
the 4xRH and 4xRE transmissions, but not in vehicles with the 41TE or
42LE fully electronic boxes.

 

No and no. The 4xRH/4xRE (where "x" runs between 5 and 7 depending on
rating) are rear-drive truck transmissions. Transmissions for vehicles
designed to tow. Minvans are NOT tow vehicles.

 

This is a 1994 Dodge Grand Caravan, 3.3l V6, and A604 trans.

 

Here we have it, in a different section of the manual:

"Overdrive can be locked out by pressing teh OD OFF button located in
the right hand pod on the instrument panel. An indicator light in the
switch button will illuminate and the transaxle will operate only in
1st, 2nd, and 3rd gear. Press the button a second time to restore the
Overdrive function.

"The O/D OFF must be selected, if desired, each time the engine is
started.

"Note: The transmission computer will overide the "O/D OFF" selection
if the transmission operating temperature exceeds acceptable limits,
to prevent transmission damage dur to overheating.

"3" Drive

"This range should be used for DESCENDING hills. The shift schedules
in this range provide improved engine braking and vehicle performance
at the expense of fuel economy. The transaxle will not shift into
Overdrive when this range is selected. Under certain driving
conditions, this will eliminate frequent shifting between 3rd gear and
Overdrive.

"When to lock out overdrive

"When driving in hilly areas, in heavy traffic, carrying a heavy load,
or whenever frequent transmission shifting occurs, press the O/D OFF
button. This will improve performance and reduce the potential for
transmission overheating or failure due to excessive shifting.

So it looks like a damned if you do and damned if you don't kinds
thing. So running in "3" is almost the same as running in "OD" with
the "O/D OFF" button selected - except that in the later case, the
computer can overide your selection if it senses that damage may occur
as a result.

Either way it looks like my fuel economy will go into the dumper.

Guess it is time to look into that trans booster cooler!

Cheers

 

It's a sign of my ignorance.

My expressing a disappointment for lack of an OD on/off switch was in
reference to the LH cars with 42LE tranny - didn't reealize yours has an
OD on/off switch. Besides locking out 4th gear, perhaps it also locks
the TC making it more suitable for engine braking (than simply manually
selecting '3')? But that is just a guess at a possibility.

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

 

Good attempt to find the meaning of all this, but wrong on this
transmission. The torque converter will lock up in 3rd gear when you're in 3
or "overdrive off" mode. It doesn't lock up in 3rd gear when the selector
is in overdrive. That's just based on my observations.

I just wonder if whoever wrote the manual was talking about the 3 speed?
Maybe screwed up? Thought "D" was different from "OD"?

 

Thanks for correcting it. I was going from LH car 42LE that has no OD
on/off button. I'm not sure about TC clutch when in '3' selected. It
was probably a mistake to try to relate the LH tranny to this - not sure
how similar/different the controls algorithms are. The lack of an OD
'on/off' button is one difference. That may be the only one, or maybe not.

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