Chrysler Minivan OverDrive activate switch

Discussion in 'General' started by vangonebuy, Jul 8, 2008.

  1. vangonebuy

    vangonebuy Well-Known Member

    Chrysler's minivan has an electronic OD lockup on their Automatic..
    I'm looking to set up a activate switch to lockup at a lower mph.

    Follow me why.
    The minimum speed for the transmission to lockup is 40MPH or +.
    But after the OD engaged you can slow down and drive with the lockup engaged as low as
    32 mph. With NO bogging.
    At 35 mph, Normal 3rd gear rpm's are approx 1800 rpm
    A switch will allow me to drive around town at 1350 rpm's.
    And not accelerate to 40 mph first.
    I'm trying to track down more transmission info to see if its possible.

    Anyone familiar enough with the wiring.

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    Last edited: Sep 14, 2011
  2. MaxxMPG

    MaxxMPG Hasta Lavista AAA-Vee Von't Be Bach

    Tom, the overdrive application is not a simple on/off on these transmissions. They have an EMCC - Electronically Modulated Converter Clutch. At speeds below about 50mph, it uses the low/reverse solenoid in the pack to progressively feed more fluid to the converter clutch to slowly lock it. By 50mph it is fully locked. You cannot feed 12 volts to directly to that solenoid, as it would burn out in 2 or 3 seconds. The solenoid switches on/off dozens of times a second to meter out the correct dose of ATF to apply the clutch. That on/off is the buzzing/ratcheting sound you hear from Chrysler automatics.

    The reason it will remain locked down to 32mph is that the algorithm is tweaked to prevent "hunting" between direct drive and overdrive.

    The best way to get the most from this transmission (known as the 41TE, the A604, or the UltraDrive - three names for the same unit) is to hypermile it and let the computer learn how you drive. It is fully adaptive and will change its behavior based on driver inputs. After a few weeks of hypermile driving, the transaxle will adjust as needed to deliver the best performance possible.
  3. vangonebuy

    vangonebuy Well-Known Member

    Great info.
    I have the 41TE.
    I've read that the computer is controlling the OD. Spent some time reviewing rebuild manuals.
    I also figured that it wouldn't be a 12 wire in. But that would be nice.

    Also tried to remove the battery and let the computer reset. No Change from before.
    Reset to the same lockup speed.
    Guess it already learned my tricks.

    But I'll keep working on it.

    My goal is only to get the transmission to lockup under 40 mph.
    It seems a shame to rush to 40 to cruise at 32-35mph in OD.
    But the difference in RPMs is big enough.

    Thanks again for the great info.

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    Last edited: Sep 14, 2011
  4. MaxxMPG

    MaxxMPG Hasta Lavista AAA-Vee Von't Be Bach

    Chrysler changed that some years ago, because simple battery changes or dead battery condtions were requiring owners to perform the "re-learning" procedure that too many were skipping. The result was a misguided opinion that the transmission was "fussy" and needed special treatment. Now, all the parameters are stored in memory that is much less sensitive to lack of electrical power. The only way to "reset the transmission adaptive logic" is via a command issued through the TCM connector. Many people who do a weekend transaxle swap to replace their burned-up UltraDrives end up breaking the new one because they don't reset the computer. The computer measures and stores the "clutch volume index" for each clutch pack and uses that amount of fluid for each shift. When slippage is detected (too much variance between measured output shaft speed and the anticipated shaft speed), it adds a little extra fluid on the next shift. So as the transmission wears, the computer remembers the ever increasing fluid volume. This provides longer transmission life via reduced slippage, and it maintains shift quality and smoothness throughout the life of the transaxle. But put in a new transmission with fresh friction plates in place of one that is badly worn, and there's now way too much fluid to apply the clutch pack. Result - blown clutch seals, damaged bushings, or in severe cases, catastrophic bind-up where two "gears" apply at the same time.

    I would say trust the Chrysler powertrain engineers on this one. Without a peek at their proprietary information, there is no way to know exactly why they set these shift points as they did. It could be to minimize "hunting" between 3rd and 4th, or to prevent engine lugging that could cause the exhaust emissions to go out of spec or could reduce the life of the engine and/or transaxle. Since all manufacturers want to brag about competitive MPG numbers, it makes sense to deduce that the engineers would allow the shift to overdrive at the lower speed if doing so did not negatively compromise another parameter.

    My best guess is that the engine is assumed to be delivering much more torque on the shift from 3rd to 4th during acceleration than it is while coasting gently down to the point where a downshift to 3rd would occur. Forcing a shift to 4th at 32-35mph during acceleration would increase the stress and wear on the torque converter clutch, which must be engaged before overdrive can apply in order to prevent overheating. Since the torque converter clutch is only partially locked at that speed, overdrive's lack of torque multiplication would only increase slippage and heat buildup in the converter clutch. And finally, I suspect it would also increase the engine load beyond what is best for engine longevity and fuel consumption.
  5. JusBringIt

    JusBringIt Be Inspired

    being that I have the same transmission in my 99 avenger and my fiancee has almost the same in her 01 sebring, I think i could also shed some light here. My avenger shifts in the same pattern as the minivan. The 01 sebring however changes to 4th gear at about 30 mph.

    Now I understand where you say you hate to go up to 40 just to cruise at 32, ( I feel the same way). I plan on doing a manual tranny swap. This is a project in the works in an alternate forum. though we may have the same transmission, the mounting may be different. The manual transmission is 5 spd of course and we can see instantly where there will be a lot of gain in city mileage by doing this swap, even highway mileage for pulse and glide.

    One of the guys on the swap also owns a grand caravan awd, so he would know what the complications are (just in case the tranny went and you wanted the manual). He's an expert at the stuff. I'm just saying this may be the only way to go around the achilles heel. of the transmission.
  6. vangonebuy

    vangonebuy Well-Known Member

    Glad to hear the Avenger can shift lower.
    I was sure it could be done.

    The transmission swap isn't an option here.
    The wife wont want to manual shift.

    What site is the swap?

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    Last edited: Sep 14, 2011
  7. JusBringIt

    JusBringIt Be Inspired is where it somewhat started

    website is: where progress is reported.

    You can go to the first site and search for 5 spd swap. there's a link at the end of that thread leading to the most up to date information.

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