I am disappointed with my G56 overdrive ratio. Until recently I was not aware that there were different gear ratio's for the G56. Mine is a 2006 behind the last 5.9 Cummins. Will the 6.7L gears and cluster from the 2007.5+ g56 transmission (with 0.74 overdrive) fit into my 2006 gear case and on the existing shafts? Any support in locating a source for this gear set would be appreciated.

G56 2006-2007.5;__ 1st=6.29, 2nd=3.48, 3rd=2.10, 4th=1.38, 5th=1.00, 6th=0.79, R=5.74
G56 2007.5+;______ 1st=5.94, 2nd=3.28, 3rd=1.98, 4th=1.30, 5th=1.00, 6th=0.74, R=5.42

 

Filll in your signature so we know what you've got.

The early 07's came with the 5.9 and I think they had the higher OD.
I can't answer your question about the gerars fitting for sure but I'm sure any good tranny shop would know. Have you considered bigger tires? My 35's really helped ans I have more than enough power with them.

 

believe 12-06 was the date when the higher od came into play

 

The gears will physically fit in the tranny case, but you're better off swapping in another G56 - the countershaft alone is ~$1500...

 

X2. Try going for larger tires. I went with 37 or if you must change to higher OD you are better off getting a used one.

 

Mine was built 12-5-06 and has the higher od ratio. Good combo! Roperteacher has one too, I think his build date was later than mine.

 

I'll have to look at my build date, it's a 2006 and has 0.79 overdrive.
DRW sets tire diameter...32" is biggest available without spacers.
I am disappointed in this poor powertrain gearing. Might just sell it because options to correct the problem are not cost effective.

Can anyone supply information so that I can externally tell if a trucks transmission is the 0.79 or 0.74 overdrive? (like a transmission part number or stamping)

 

Lotsa people put bigger tires on duallies.

 

3:42 gears are available for our axles. Lots cheaper than selling the truck for an auto. The 0.79 final drive has worked well for me with the 285-75-17's and camper load. No new clutch so far.

 

I have found through some research that the sticker on the case will end in AD if shorter gear/older vs. AE for the later trucks with the taller gear. I have an early 07 now and it is early enough to still have the AD suffix. I'm over 2100 RPM at 70 MPH with 34 inch tires.

 

also, the g56s came in the mid to late 05s as well...mine has one. i love the gearing in my truck w/ the exception of the overdrive as well. i'm not too happy w/ it...but i did go to a 33" tire and it dropped my rpms by 100. but i later plan to run a gearvendors overdrive to help w/ my gearing...if money permits down the road.