71 GMC C3500 4:10 Rear End Ratio???

[TreverSlyFox]

Was just going through the 1 ton dually I picked up 2 weeks ago and was looking over the Glove Box Spec. Sheet.

According to the sheet this 71 GMC C3500 came with a 4:10 rear end ratio along with the 350 cu in and the SM465 4-speed. This must have been a delivery truck, it has an Electric over hydraulic lift gate (still works) and a 9' 6" flat bed. Is there an EASY way to check the rear end ratio out?

Maybe the number of turns the drive shaft rotates per 1 turn of the rear wheels? ( I have no idea what that would be).

Would the numbers on top of the axle housing (if I find them) tell me?

Sure would be nice if it still has a 4:10 rear. My other C3500 is screaming at 70 mph so I keep it at 60mph but the 350 is still turning some high Rs.

Oh, this is another 350 engine with no numbers stamped on the boss that sticks out below the passenger side head up front. Body and frame numbers match the title, I must be living right.

[Rod]

I've gone through a couple duallies and 4.10 is fairly common in 71 and 72's. Pop a cover and check if you like. There may be numbers on the diff to tell you a code to what it originally came with - but that dosent mean it's still there.

[lukecp]

You're in Houston.....what a small world. I'm from Willow Springs, although currently in Rolla. Welcome to the board!

I would pop the cover and check. The fluid proably needs to be changed anyway. I know on the 12-bolt rears the number of teeth are stamped on the ring gear (41 10 for 4.10), but i'm not sure about the HO72 that you proably have on there.