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sangell · 02-16-2017, 03:29 PM

What is your t56 out of? They had different ratios, the most common behind the LS motors are the F-body version with a .50 6th. In my son's truck we have a CTSV T56 with the .56 6th gear and 27" tires. I put a 4.56 in it. With the low rear gear and high OD ratios you need to watch out for drive shaft RPM. His truck was a long bed and I tried to run a one piece shaft that didn't work out. With 27" tires, .56 6th gear it was 2400 rpm at 75mph which put the drive shaft at 4300 rpm and it was not happy. The drive shaft is a 4"x.083 wall steel piece. We have since cut the truck down to a shortbed so that makes the driveshaft 12" shorter and I'm dropping to either 4.10s or 3.73s. I think the 4.10s are the way to go but the 3.73s help so much with the drive shaft RPM.

02-16-2017, 03:29 PM	#6
sangell Registered User Join Date: Jun 2015 Location: Overland Park KS Posts: 173	Re: rear end gear ration for t56 What is your t56 out of? They had different ratios, the most common behind the LS motors are the F-body version with a .50 6th. In my son's truck we have a CTSV T56 with the .56 6th gear and 27" tires. I put a 4.56 in it. With the low rear gear and high OD ratios you need to watch out for drive shaft RPM. His truck was a long bed and I tried to run a one piece shaft that didn't work out. With 27" tires, .56 6th gear it was 2400 rpm at 75mph which put the drive shaft at 4300 rpm and it was not happy. The drive shaft is a 4"x.083 wall steel piece. We have since cut the truck down to a shortbed so that makes the driveshaft 12" shorter and I'm dropping to either 4.10s or 3.73s. I think the 4.10s are the way to go but the 3.73s help so much with the drive shaft RPM. Last edited by sangell; 02-16-2017 at 03:35 PM.