MY 2012 is supposed to lock out of 6 in tow haul mode. ALSO in manual shift you're SUPPOSED to be able to lock iy out of 6th gear. You can not. At 65 MPH in 6 you're turning 1600 RPMS. WAY too low rpms!! Chrysler engineering says this is not right but I'm beginning to wonder if they know how to fix it, they sure are taking their sweet *** time!!

 

yeahhhhh ummmm, good luck with them fixing it right.
These dealers today are incompetent as they come.
Have they even tried reflashing it for you yet...?

 

No! Been 2 weeks and "engineering" hasn't even looked at it yet!

 

I think there needs to be an understanding on how the 645RFE works. The 654RFE is essentially the same as the 545RFE that preceded it.


The 545RFE and 645RFE use the same transmission case and internal drive architecture with a different torque converter for 645RFE. The major difference between the 545RFE and 645RFE is the latter uses all six forward gears sequentially in the Electronic Range Select mode, but uses the 545RFE shift sequence in the normal drive mode. When in the normal mode, the 645RFE operates like a 545FRE and never uses 2nd and 3rd in succession (3rd becomes 2nd prime).


The 545RFE (1999-2011) has the following gear ratios:
1st = 3.00:1
2nd = 1.67:1
2nd Prime = 1.50:1
3rd = 1.00:1
4th = 0.75:1
5th = 0.67:1
Rev = 3.00:1

The 645RFE (2012) has the following gear ratios:
1st = 3.00:1
2nd = 1.67:1
3rd = 1.50:1
4th = 1.00:1
5th = 0.75:1
6th = 0.67:1
Rev = 3.00:1

Note that 1:1 direct drive is 3rd gear on 545RFEs, and 4th gear on 645RFEs. Overdrive begins at 4th gear on 545RFEs, and 5th gear on 645RFEs.

In both 545RFE and 654RFE transmissions, selecting Tow/Haul Mode shuts off MDS, utilizes a prolonged shift schedule in all forward gears, uses the 2nd prime as 3rd gear, and prevents torque converter lock-up in 4th & 5th gears (545RFE) or 5th & 6th gear (645RFE).

When selecting Tow/Haul mode in the Drive position on 545RFEs, 5th gear will be displayed in the EVIC display. However, the highest gear is actually 4th gear because the transmission shift sequence is changed to 1st, 2nd, 2nd prime, 3rd, then 4th (first overdrive) in Tow/Haul. Even though the EVIC is displaying 5th gear in Tow/Haul, that gear is actually 4th gear.

Since the mechanicals between the two transmissions are the same, I would expect that the same thing would happen on the 645RFE. Which means that even though the EVIC displays 6th gear in Tow/Haul mode, I venture to guess that if you count shifts there will only be five. If this isn't happening, my first suspicion is the PCM/TCM is not receiving the correct signal when the Tow/Haul mode switch is pressed even though there's an indication on the instrument panel that it's been engaged.

Best regards,
Dusty

 

Kudos, Dusty, for the excellent explanation!

 

Tunaman, I think I have discovered a (the?) problem.

Just to verify, you have a 2012 Ram 1500 with a 5.7 motor. Correct?

Regards,
Dusty

 

That's all well and good Dusty. I'm not going by #s on a dash display. For example in the man. Mode it says 5 even when it does the 5 to 6 back to 4 up to 5 crap. But the tach Doesnt lie, at least for comparison purposes. And 1600 rpm at 65 is NOT going to be enough RPM for the engine to maintain. When not towing, fine! But with 4000-5000 lb boat, ain't gonna happen. why it shifts to 4 to 5 back o 6. All the while saying 5. Is everyone wrong, including Chrysler in saying when in man shift, you're supposed to be able to lock it in 6th? Or in tow mode it's supposed to look out of 6? I ould care less what little # is on the dash, it means nothing. Now, with manual it WILL lock in 1,2,3,4 but not 5. Do you not agree it should not shift 30 - 40 times at 65 in 150 miles? Actually probably more like 50 times. I guarantee the tranny will burn in a trip to the keys. (700 miles ound trip) oh well, Dodges nickel! Let's not get bogged down with #s on the dash. The only # on the dash I get oncerned with is oil temp and water temp, and they jump when this is going on.

 

Sorry Dusty, I did not see you're second post. Yes, 2012 ram 1500. 5.7 with ( unfortunately) 3.56 gears. But regardless of gear, the tranny should not be oing what it's oing. do I know why? Nope! But I know it's not right.

 

You do understand that the 'manual' shift doesn't "lock" the transmission in a gear? That shift mode allows you to set a limit on the highest gear the trans can shift up to. If you set it to 4th, for instance, the transmission will shift up and down all it wants between 1 and 4 as conditions warrant but will not shift up to 5. Manual mode is a top gear limiter.

If you're driving around towing a trailer with the trans in manual mode set at '5' and the transmission is 'shifting' then either the transmission is actually shifting around between lower gears (i.e. 3, 4, 5) or it is locking and unlocking the torque converter. Both of those scenarios will change the RPM and will feel like a shift. It is not shifting into a higher gear.

How and when it shifts depends on a ton of things, including uphill, downhill, head winds, tail winds, and what you're doing with your foot on the accelerator. Shifting up and down a lot may be perfectly 'normal' for the driving conditions you were experiencing. It isn't preferred, I agree, when towing. So next time use manual mode and limit the top gear to one lower than you were using. That should eliminate the gear hunting. In all likelihood there is nothing wrong with your transmission's behavior.

Rob

 

I agree with BBE that's it's probably the torque converter going in and out of lock or into partial lock or whatever they call it. I've seen similar behavior on my '09 when towing. The RPMs will move around without the trans shifting. The way I can tell what is going on, is that when not towing, I now what the RPMs are for all of the gears when the TC is locked for certain speeds (60 or 65 MPH). When towing at the same speeds, there are other RPMs that don't match the no-load TC locked ones. I always assumed it was the TC unlocking on purpose before going into a down shift.