I dont know if this car came with 5.7 or 5.0, or manual or auto. cause the last owner swap in a 6.6l with th400, but he say the rear end was all factory, he dint touch it. So what kind of rear end do I have and how many bolt ? thanks

 

Unless you crawl under the car to have a look, it's only a guess. It's probably a Borg Warner 9 bolt with 3.27 gears. The other option is a 7.5" 10 bolt.

Looking under the car to count the bolts on the diff cover can tell you if it's a 9 or 10 bolt but that's all the information you'll be able to get without taking the cover off the diff to see exactly what's inside. Never assume it's still original.

 

if there's a rubber plug on the diff cover it's a 9 bolt.

 

I count this morning and its 10 bolt



so what kind of gear and when I change the gear oil do I have to add gm additive ? thanks

and btw how much power is these 10 bolt can hold ? thanks

 

What Gear Ratio Do I Have?
Jerk the diff cover. The numbers are stamped on the ring and pinion. The RPO’s are usually found in the center console:
41 : 15 = 2.73 (RPO GU2)
41 : 14 = 2.93 (RPO GU3)
40 : 13 = 3.08 (RPO GU4)
42 : 13 = 3.23 (RPO GU5) / Approx. RPM’s at 70 mph--2133
41 : 12 = 3.42 (RPO GU6) / Approx. RPM’s at 70 mph--2255
41 : 11 = 3.73 (RPO GT4) / Approx. RPM’s at 70 mph--2463

Or from Randy’s Ring and Pinion:
Jack up one tire if you have an open diff, or both tires if you have a working posi or locking differential. Rotate the tire one full revolution for posi’s and lockers and 2 full revolutions for open diffs. Carefully count the number of full revolutions the driveshaft makes. This is your gear ratio. In other words, if the drive shaft turns 3 ¾ turns, you probably have a 3.73 gear ratio. Turning the tire for twice the number of full revolutions and dividing the drive shaft revolutions by two will give you a more accurate reading.

Axle tube codes can be found in the following link (though rust usually makes them indecipherable, and they, like the RPO codes, indicate how the car was equipped new, and not necessarily what’s currently in place): http://sethirdgen.org/reardata.htm

Additive if the rear has limited slip.



JamesC

 

Thanks all ! im plan running redline 75w90 gear oil on it, im just wonder if redline is good for these rear diff ? any body have any recomment ?