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-   -   The 6-speed trans... (http://www.ramforumz.com/showthread.php?t=95895)

DodgeRamMan71 11-06-2011 01:21 AM

The 6-speed trans...
 
Has anyone seen how the newer RAMS with the 6-speeds get exactly the same MPG's as our 5-speeds. I do not know a lot about the transmissions, but I am wondering if it has to do with a software upgrade? I was reading about it and it seems there are more gears in our 5-speeds and the extra gear is used for a kick down gear. I am just wondering if our 5 could be 6's with a software upgrade.:4-looney:

GTyankee 11-06-2011 01:27 AM

You are correct
The 545 RFE 5 speed
the 45 RFE 4 speed, first used in the 1999 Jeep
the 65 RFE 6 speeds are all the same transmission
so is the 68RFE
the 6 speed also got a upgraded torque converter
everything else was just a software change

RFE stands for Rear wheel Drive, Fully Electronic

Gene K 11-06-2011 04:39 AM

66RFE (2500 Hemi) and 68RFE (Cummins) have different gear ratios with lower 1st and taller 6th and more even splits.

45RFE / 545RFE / 65RFE
3.00 / 1.67 / 1.50 (Kick Down in 545RFE) / 1.00 / 0.75 (Top Gear in 45RFE) / 0.67

66RFE / 68RFE
3.23 / 1.84 / 1.41 / 1.00 / 0.82 / 0.63

DodgeRamMan71 11-06-2011 04:31 PM

I am gonna keep my RAM at least until the 8-speeds come out. They should get better MPG's and also better take off power. I have never went up against a Tundra, but I hear they are quick. Oh well I was wondering about the 5 & 6 speed thing, it did not make sense as to why it did not squeeze out at least 1 mpg better.

snrusnak 11-09-2011 02:37 PM

The mpg is not any better because it is literally the exact same physical transmission. The rams before 2012 have a 545rfe "5 speed" transmission, but it actually has 6 forward gears. One of the gears is in between 2nd and 3rd and is called 2nd prime. It is mainly used for downshifting only. When you select tow/haul mode the gear pattern gets changed to eliminate the 2nd overdrive gear, and make the 2nd prime the 3rd gear, 3rd becomes 4th, 4th becomes 5th. The 2012 "6 speed" is the same it just has different programming so it always uses all six forward gears. 2nd and 2nd prime are so close in ratio that mpg is unaffected. IMO they did this to be able to market their truck as a "6 speed". Only other change was the torque converter. The predecessor to the 545rfe in chryslers was the 45rfe(still again the same physical transmission, just programming differences).

45rfe:
1st 3.00:1
2nd 1.67:1
2nd Prime 1.50:1
3rd 1.00:1
4th 0.75:1
Reverse 3.00:1

545rfe:
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
Reverse 3.00:1

545rfe in tow/haul mode:
1st 3.00:1
2nd 1.67:1
3rd 1.50:1
4th 1.00:1
5th 0.75:1
Reverse 3.00:1

65rfe for 2012 rams:
1st 3.00:1
2nd 1.67:1
3rd 1.50:1
4th 1.00:1
5th 0.75:1
6th 0.67:1
Reverse 3.00:1

Turbovsix 11-09-2011 02:48 PM

snrusnak -

Just help me understand - so in my 2010, are you saying that in normal driving, with tow/haul NOT selected, the only time I'm using 2nd prime is when downshifting from third? Is it not used on the way up? Sorry, a bit of a trans novice, and the only time I've ever really thought about gearing like this is (2nd prime, etc) when talking about big rigs.

So in the 2012's, you're saying that while the gearing is essentially the same, 2nd prime is just eliminated and becomes third.

What's the logic behind making it an overdrive for second?

Thanks for the good info -
Rich

snrusnak 11-09-2011 02:53 PM

Quote:

snrusnak -

Just help me understand - so in my 2010, are you saying that in normal driving, with tow/haul NOT selected, the only time I'm using 2nd prime is when downshifting from third? Is it not used on the way up? Sorry, a bit of a trans novice, and the only time I've ever really thought about gearing like this is (2nd prime, etc) when talking about big rigs.

So in the 2012's, you're saying that while the gearing is essentially the same, 2nd prime is just eliminated and becomes third.

What's the logic behind making it an overdrive for second?

Thanks for the good info -
Rich
First of all I didn't mean to be confusing with the term "2nd overdrive". When I say "2nd overdrive" I'm referring to 6th gear(the second overdrive gear), not 2nd prime.

What you said is correct. The ONLY other time in your 2010 that you would be able to accomplish using 2nd prime in a normal upshift is by using the ERS(electronic range selection) (I think that's it's name)....the +/- button on the shifter. If you use that it will upshift using all the gears (I'm pretty sure). This is the reason why people should not be selling their trucks with the 545rfe to "upgrade" to a 65rfe, as you can drive both using all the gears (although doing so in the 545rfe disables mds).

snrusnak 11-09-2011 02:55 PM

Oh and the logic for the 2nd overdrive (6th gear) was highway fuel economy. The logic for the 2nd prime downshift gear was to ease downshifts and maybe also for tow/haul mode. Mainly for downshifts though.

Turbovsix 11-09-2011 11:09 PM

Thank you sir - yes, I confused the terminology there. Makes sense now.

TransEngineer 11-11-2011 03:25 PM

Quote:

Originally Posted by snrusnak (Post 652666)
Oh and the logic for the 2nd overdrive (6th gear) was highway fuel economy. The logic for the 2nd prime downshift gear was to ease downshifts and maybe also for tow/haul mode. Mainly for downshifts though.

Sean, you are right, the 2nd overdrive ratio is for fuel economy, and 2nd Prime gear is used for 4-2 (well, actually 4-2P) downshifts. The 2nd Prime ratio is 1.500, whereas 2nd gear is 1.667. So using 4-2P for a kickdown gives you a smoother (smaller) ratio change, and also allows kickdowns at higher speeds (where a 4-2 kickdown would put you too close to engine overspeed). In addition, to make a 4-2 downshift, the trans has to make two clutch-to-clutch handoffs (releasing the OD and 4C clutches, and applying the UD and 2C clutches). But the 4-2P shift involves only a single clutch swap (OD to UD), so it's an easier / smoother shift.

The 4-2P downshift is used in both normal Drive mode and in Tow/Haul mode.


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