rear gear ratio change VRS G56 gear change

[TowPro]

So far I have heard that 2007 has a different OD in the G56, plus you can buy 3:42's for 07.

I just checked out the service manual on the G56. It looks the 6 gear change would require a complete counter shaft gear cluster (read $$$$$), and would require a trans taredown.

Looks like the rear ratio change would be the best bet cost wise.

I have not priced the trans parts.

 

[jmccart]

Good info. I am waiting to get 315's to counter the crappy O. D. in my G56.



Thanx.

 

[DHuffman]

I read a post somewhere that said the G56 in the '07s had a taller OD - mine turns a little under 2000 RPM @ 65 mph w/ stock tires... what are the '06s turining @ 65 mph?

 

[TowPro]

I read a post somewhere that said the G56 in the '07s had a taller OD - mine turns a little under 2000 RPM @ 65 mph w/ stock tires... what are the '06s turining @ 65 mph?

I think mine is just a Tad over 2000 at 65. Do you have the 5. 9 or 6. 7?

 

[DHuffman]

5. 9L ... So maybe they did change the OD ratio.

 

[DHuffman]

6-7l-engine-transmissions-2007-5/183535-new-g56-overdrive-ratio



The above post mentions a new 0. 742 ratio for 2007. This seems to be the ratio in my truck. I wish they would have went with 0. 70...

 

[RodMorris]

My '07 with the 5. 9 and G56 turned about 2100 at 65 with the stock 245's. It turns about 1950 with 285's.

 

[RodMorris]

Continued:

I take that to mean the new overdrive gears are for the 6. 7 motors.

 

[DHuffman]

Continued:



I take that to mean the new overdrive gears are for the 6. 7 motors.

Not really... 245s are smaller than 265s; also, have you recalibrated your speedo for the 285s?



To figure it out, do the math:



65 mph = 1. 0833 miles/min

Per BFG, 265/70R17 = 658 revs/mile

1. 0833 x 658 = 712. 833 revs/min (@ tires)

712. 833 x 3. 73 = 2658. 868 revs/min (driveshaft)

2658. 868 x . 742 = 1972. 88 RPM ~ this is what my tach is reading.



Later

 

[RodMorris]

Haven't re-calibrated the speedo, but I have calculated the difference using highway mile markers and GPS. It's off about 7. 5%, and I'm running 1950 rpm at a true 65 mph.

 

[DBusch]

wow... maybe i need to grenade the G56 in my 2006 so i can get a new 2007 transmission under warranty... LOL!