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!

Reply to
NewMan
Loading thread data ...

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

Reply to
Ted Mittelstaedt

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')

Reply to
Bill Putney

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')

Reply to
Bill Putney

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.

Reply to
Steve

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.

Reply to
NewMan

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

Reply to
NewMan

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.
Reply to
Steve

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.

Reply to
Steve

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

Reply to
NewMan

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

Reply to
NewMan

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')

Reply to
Bill Putney

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"?

Reply to
Joe

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')

Reply to
Bill Putney

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.