The Stovebolt Site Forums The Shop Area Engine Shop Rear end ratio identification?

My son and I are pulling the rear axles on our '66 C10 to do the wheel bearings. When I took off the rearend cover, the gears looked great, real good shape with no noticable wear, enough to make me wonder if someone had swapped out the original stump pulling gears with a better set for the highway. Hopefully they did, because we were going to do that anyway down the road. Is there any way to tell what the ratio is by looking at it? I don't know too much about gearing.....

If it makes any difference, its got the 4 speed manual with the granny gear.

If you still have the cover off, just count the number of teeth on the ring gear and the pinion gear, then divide the ring gear count by the pinion count. If you already put the cover back on, just turn one wheel 2 revolutions while counting the number of driveshaft revolutions. 3 driveshaft revolutions = 3.07:1, 3 3/4 revs = 3.73:1, etc. If it's a posi-trac then you will have to turn both wheels a full revolution. Hope that helps.

Heres where I reveal my lack of rear end knowledge...The ring gear is the big one, and the pinion is the one on the end of the driveshaft, right?

Thanks

Right.

Thanks, thats exactly what I was looking for.

The tooth counts for the ring gear and the pinion gear are probably stamped on the ring gear. Divide the larger number by the smaller number to get the ratio.

Counted the teeth, looks like its got 4:11 gears in it. Ouch...Thats NOT highway gearing! Guess I'll put that on the list for future upgrades...At least they are in good shape, I'll run em for now.

Yes, those are very low, especially for driving in today's traffic without an overdrive. The 4.11's were an option as well as the 3.07. The 3.73's were pretty much standard from 63-66. I have seen very few of these trucks with the 3.07's.

I will probably go with the 3.73 (?) or a 3.5ish gear. I want to be able to keep up on the freeway, and save a little gas, especially since my son will be the one trying to keep the tank full! I have the 4 speed transmission, so I will have as much torque as I want and then some in 1st! That gear is really nice in traffic, too...

Erik,

Just me talking here, but 3.73 gears really won't be that much of a jump. With the 4 speed you could go a bit higher and still have the low gear to get rolling. A few years back I put a 3.07 rear end from a '70(still 6 lug) in an a '64 I had. It had the 230 six with the 3 speed, it pulled just fine and after a few carburetor adjustments I was getting 17-18 mpg. It would cruise along all day at 65-70 mph with no problem. Of course, I was not pulling anything with it on a regular basis either. I did haul another truck with it on a 16ft trailer a couple of times, but as long as I let it take it's time it was no problem.

Like I said, this is just my opinion. I have always liked taller gears but that's just me. I'm sure others have their preferences as well.