Highway numbers, rear gear question

[infinite-foamies]

I have an 88' F350 XLT Lariat Centurion package CCLB dually 7.3 with an ATS turbo. Not new to the truck and have been on FTE and other forums just never joined here.

Cruising at 70 mph with a C6 and GV in OD I am spinning ~3000 RPM with LT235/85/16's on Alcoas(all six).

Using a rear gear calc my rear gear is about a 5.86, does anyone know if this was produced for the Sterling 10.25 with LS? Or is my math wrong?

 

[OLDBULL8]

One way to tell for sure what the rear gearing is. Mark the drive shaft, mark the tire, turn the tire one revolution, count the drive shaft revolutions. If you have a 5:56, the drive shaft will turn that many times. I would bet you have a 4:10 rear.

 

[laserjock]

Remember that your gear calculators assume a lock up of the driveline to the engine. C6 does not lock so it will always calculate lower if you are using the tach reading in the calculator. Like OLDBULL said, its probably 4.10. Check your door tag. It should give you an axle code that you can search here or google.

 

[icanfixall]

Welcome to the forum. I do not recall if that high of a gear set was ever offered for this truck but 4:10 was offered. I agree with what has been posted above too. Lifting and marking the driveshaft and tire is about the simplest way to determine the gear ratio.

 

[Matt_INW]

Hmm, I have a 4:10 and I'm ~2500rpm at 70. Don't have the C6 though, have the E4OD.

 

[jayro88]

Hmm, I have a 4:10 and I'm ~2500rpm at 70. Don't have the C6 though, have the E4OD.

You wpuld have lower rpms than a c6+gvod. The e4od has a deeper OD ratio (.71 vs .8 iirc), plus your torque converter locks while the c6 doesnt.

I would vet he has 4.10s if it is the factory rearend. Anything much higher and it would have been an add on, probably to assist heavy towing.

 

[infinite-foamies]

I will get to turning the driveshaft eventually. I know a 4.30, 4.88, and 5.38 gear set was offered for the Sterling 10.25 and I know I have a Sterling 10.25 still.

GV is a .78 ratio.

 

[hesutton]

I know a 4.30, 4.88, and 5.38 gear set was offered for the Sterling 10.25 and I know I have a Sterling 10.25 still.

Those gears were not a factory option on a '88 F350... unless Centurion swapped the gears after it left the Ford truck plant.

F350 SRW's were either 3.55 or 4.10. F350 DRW's were 4.10 from Ford.

Heath

 

[F350camper]

Are you using your speedo to determine speed? Or a gps? If you are using the speedo, its possible you have the wrong speedo drive gear and or driven gear for your setup. Its also possible that one of them is chewed up and is giving you false readings. In either of those cases, it will be off more the faster you go.

 

[infinite-foamies]

It also did not leave Ford with a Gear Vendors so who knows what else was changed.