3.42 rear end for '08 G56?

[AHarris]

I saw an earlier post from TDRAdam alluding to the '08 trucks w/G56 6-speed manual getting a 3. 42 rear end to keep the RPMs down. Is this true? If so, could someone with a 07. 5 6. 7L/G56 Combo swap the 3. 73 gears for 3. 42's without screwing something up?

 

[CUMMINZ]

If you both have same rearend and it is not a 4x4.

 

[MCummings]

I wonder if 3. 42's are available in 4wd?



It would be so sweet to have a 68RFE and 3. 42's. Talk about a highway cruiser!



Merrick

 

[AHarris]

Huh?

If you both have same rearend and it is not a 4x4.

Why not a 4 X 4? Can't you change the gears in the front pig too?

 

[CUMMINZ]

39

You mentioned in your first post "3. 42 rear end". I took for granted you were wanting to just change out the "rear". Yes you can change out both.

 

[AKaiser]

I wonder if 3. 42's are available in 4wd?



It would be so sweet to have a 68RFE and 3. 42's. Talk about a highway cruiser!



Merrick

From everything I've read, the 68RFE and 3. 42s would be a redundancy. Let's compare OD gear ratios. From http://www.klenger.net/dodge/general-reference/gear-speed-calculator.pdf



NV5600: . 73

G56: . 79 (or . 742 after Dec 06)

68RFE . 816 (5th) and . 625 (6th) essentially a 4speed w/2 ODs.

NV4500: . 75

48RE: . 69



The 68RFE with 4. 10s is turning 1900 RPM at 70 with 4. 10s and 77 MPH with 3. 73s. Do you really see the need for 3. 42s with a 68RFE? The 68 w/3. 73s is turning right at 1600 RPM at 65 MPH in 6th, right at the lower max torque RPM.



BTW, based on these numbers, it looks like 4. 10s would be perhaps a bit slower than necessary.

 

[CUMMINZ]

essentially a 4speed w/2 ODs.





The 68rfe is a long ways from a 4 speed with 2 ODs. The 1st & 2nd. are lower that a 48re's 1st & 2nd. Makes for much better launches.



CUMMINZ

 

[courierdog]

I would love to have 3. 42 in the rear end as most of my work is done at highway speeds running light.
Running at lower rpm's will help the Milage as well as redce the soot build up.
If you read cummins recommendations they recommend running lower RPM.
It is Chrysler who insisted on the 3. 73 and 4. 10 only for the new engine on the initial production run.

 

[RDHamill]

My '01 with NV5600 & 3. 55 was perfect, had this combo been availible on my '07 I would have stayed with the manual transmission. if there is any truth to the 3. 42 / G56 for '08 , I just might consider trading !!!

 

[AKaiser]

essentially a 4speed w/2 ODs.





The 68rfe is a long ways from a 4 speed with 2 ODs. The 1st & 2nd. are lower that a 48re's 1st & 2nd. Makes for much better launches.



CUMMINZ

I get what you're saying, but 5th and 6th are OD gears. By definition, an OD gear is any gear that causes the output shaft to turn faster than the input shaft. The old 47/48REs were 3 speeds with an OD. The 68RFE is a true 4 speed with a double OD, which is why it has a lower first gear, and closer gear spacing. No, it's not the 48RE with two addl gears added. If that's what you meant, you'd be correct.

 

[AHarris]

Thanks

You mentioned in your first post "3. 42 rear end". I took for granted you were wanting to just change out the "rear". Yes you can change out both.

Thanks. So, if I changed the ring and pinion to 3. 42 in both front and rear differentials, what would I need to do to ensure the speedometer and the electronics on the 6. 7 aren't screwed up?



Reason I'm asking is I'm in the process of buying a 2007 QC 3500 6. 7L 4 X 4 SLT with the G56 6-speed. The 68RFE sounds good but this is too good of a deal to pass up--I'm getting this thing for $31K!



Any idea what the costs involved would be switching to a 3. 42?

 

[AKaiser]

Thanks. So, if I changed the ring and pinion to 3. 42 in both front and rear differentials, what would I need to do to ensure the speedometer and the electronics on the 6. 7 aren't screwed up?



Reason I'm asking is I'm in the process of buying a 2007 QC 3500 6. 7L 4 X 4 SLT with the G56 6-speed. The 68RFE sounds good but this is too good of a deal to pass up--I'm getting this thing for $31K!



Any idea what the costs involved would be switching to a 3. 42?

As far as the speed sensors, I believe (don't quote me) the ABS sensors on the axle itself control that, so the only changes you would need to make are if you put larger/smaller than stock tires.



As for swapping, check on your RPMs. You may have the "AE" model G56 with a . 74 top gear instead of the . 79s found in the original "AD" model (05. 5-06) that are the complaint. Does your truck hit 64 MPH or 68 MPH at 2000 RPM in 6th? If I had that model G56, which they started putting in the trucks in 2007, I wouldn't worry about the 3. 42s, but that's just me and "one man's opinion. " You can look at the klenger.net pdf that I linked earlier in this thread. Go to page 2 and compare the two trannies and you'll see what I'm talking about.

 

[Turbo Tim 1]

If anyone dumps a set of 3. 73's for a set of 3. 42's I would be interested in your 3. 73's! The wifes truck has 4. 10's and I don't need them that low.

 

[Motorhead]

As for swapping, check on your RPMs. You may have the "AE" model G56 with a . 74 top gear instead of the . 79s found in the original "AD" model (05. 5-06) that are the complaint. Does your truck hit 64 MPH or 68 MPH at 2000 RPM in 6th? If I had that model G56, which they started putting in the trucks in 2007, I wouldn't worry about the 3. 42s, but that's just me and "one man's opinion. " You can look at the klenger.net pdf that I linked earlier in this thread. Go to page 2 and compare the two trannies and you'll see what I'm talking about.

I just bought a 2007, 5. 9 G56 that was produced in 12-06. It has the AE, . 74, 6th. A neighbor bought the same truck but his was produced in 8-06. It has the AD, . 79, 6th.

I honestly think that 3. 42's would be too high for the new 68RFE.

My 2001. 5 had the 3. 55's and while I didn't have 2 OD selections, With MODS, OD was too high for most HEAVY towing.

So some early 2007's had the AD trans.

Just some info I found.

 

[jmorse]

I had a '99 3500 C&C w/5spd. and 4:10 rear. I traded to an '07 3500 C&C w/G56 and 3:73 rear. The '99 had 16" tires, while the '07 has 17". My experience with the two trucks leads me to believe the 3:42 rear would be useless in most applications. With the '07 there are times I can't use 6th gear. I think the 3:42's would make for a lot of shifting and make the truck not fun to drive. I love my '07 and I am happy with the gearing. I'm getting better milage than the '99 did and can still move a mountain.



Jim

 

[gsbrockman]

Talk about a highway cruiser!

My 2007. 5 w/ LT285/70R17 Firestone Destination A/T's and re-calibrated speedometer turns 1,350 rpm at 55 mph and 1,700 rpm at 70 mph.



3. 42's are overkill with the 68RFE.



Greg

 

[RDHamill]

I would agree that 3:42 would be too tall for stcok tire size and the 68rfe.

The 3:73 is just fine.

However, 3:42 would be a great option for use with the G56.

Unless they'd like to add a seventh gear !!!!!

thanks guys

 

[KEpperly]

I want 3:73's also. If anyone is thinking of changing out there 3. 73 let me know. I could finally feel like im not beating on my truck to keep up with traffic

 

[RDHamill]

I checked the specs for the Rams for 2008. I see no mention of a 3:42 option.

maybe it will come as an update, if at all !!!

 

[metwuk]

There is option for 3. 42's with G56. Was at dealer today and found out but not clear if 4x4 or 4x2 limitations.

The dealer didn't know anthting about 08, think they had to call somebody about ratio.



Chrysler's really on the ball sellin' 08's and no literature.

Wouldn't know what to order if you wanted to.



Backwards!