Rear end options?

[Ratfab]

Hey all, I just picked up a '68 Gmc 2500. The gears in the rear are crazy steep.
At 45 mph the motor's screaming. Not sure what rear end it is. Dana 60? 10 bolt, 8 lug & floating axles. T350 trans. Thinking about swapping in a 1/2 ton, 6 lug rear. Any ideas/suggestions would be appreciated.

[c10JIME]

looks like a dana 60 to me ,could be wrong but pretty sure

[rocks409]

Ratfab, I hope you don't mind me jumping in here but I have a similar situation. '70 C20. You probably have 4.57 ratio, mine is 4.10, but I wonder if a simple ring gear and pinion change to 3.54 is possible in the C20 rear ends. I'm sure someone here has the answer.

[SS Tim]

Case split on the Dana 60 ratios is 4.10 down and 4.56 up. So on a 4.10 you could regear to a 3.54 on the same case (open or posi). But with a 4.56 you need to replace the case to go down at all.

[Ratfab]

Thanks sstim. I was leaning toward a rear end swap anyway.

[sapper4]

A 3.54 gear swap is possible. I think the easier and cheaper way would be to swap to a 14 bolt since you already have leaf springs. I pulled a 14 bolt from an 87 four wheel drive suburban with a 3.42 gear. The spring perches mounted perfectly. I had to relocate the shock mounts and buy larger u bolts (since I didn't get them from the donor). The drive shaft even bolted back up.

[k29349]

That is a Dana 60. You could probably find a big or small 14 bolt pretty cheap with 3.73 or 3.54 gearing. That would allow you to keep 8 lugs. If you still need less gear you could go with taller tires.

[Ratfab]

Sounds like it's time to hit the junk yard. Thanks all.

[cool68]

no matter what you do be sure to verify that "new" rear gears are what will work best with your drivetrain/tire size, etc - project33.com has a good calculator.