The Stovebolt Site Forums The Shop Area Engine Shop 1970- where to find the diff. ratio

I have a 1949 3/4 ton pickup, and want to possibly swap the rear end gears with a late 1960, early 1970 Chevy 3/4 ton. . . It looks like the same diff. and people have told me it is the same, so I guess it is.

Anyway, it is a 1970 give or take, in the glovebox, the sicker says it has no slip diff. (would that change anything as far as fitting?) Coil springs on the back, and that is about all I know.

All of you guys are going to tell me to just jack it up, but the whole box is stacked full of old Iron, and it would take 1/2 a day to get the junk jards forklift to it. So where are the numbers I need (if they exist). I could not see any tags on it anywhere, but if they are stamped in. . . .

Thanks

Brian Kemp

Also, what gear ratios were availible those year?

I have about the same question - my local boneyard has two '69-'70 Chevy 3/4 ton pickups with the coil spring rear ends. One had an automatic (I checked it, it appears to be the 4.11 rear), the other had a 4-speed and has already had the axle shafts removed. Does anyone have a clue what the gear ratio would have been on the 4-speed? I checked every place on the truck I could think of, no luck.

I am going back tomorrow, so please answer soon!

The book I have he say's in 1969 the 3/4 and 1 ton truck code is stamped on the forward upper surface of the differential carrier housing.

For 1970 the numbers are said to be stamped on the bottom of the left or right axle tube adjacent to the differential carrier housing.

Possible gear ratios on the 3/4 ton:

3.73:1
4.11:1
3.07:1

This is only for the Chevrolet trucks.

Joe

You can pull the diff cover and count the teeth on the pinion and ring, the gear ratio is just the ratio of teeth.

You won't find the information on the truck it self. Most GM axles have a two letter stamp in the axle tube out by the brake backing plate. Most are on the passenger side of the axle. If you do fine the code, ( AX, AD, Etc...) you will need a shop manual for that year to tell what the code means. The best way to find out is to pull the cover and check the part numbers and date code. The ring gear should be marked with all the information, ratio, date, and number. If you can't turn the axles due to weight on truck, you may be stuck. You can't count the teeth if you can't turn it, and you read the numbers if they are on the back side.

Try taking a wire brush over the axle tubes and check for codes. At least get the engine and transmission type from the truck. If it wasn't special ordered, someone should be able to get close on the ratio.

As for fit, Posi-traction won't make any difference. It is a internal anti-spin carrier which the ring gear bolts to. Joe

You will find the ratio numbers just inside the edge (flat area between the bolt threaded ends)of the ring gear(teeth side). You will need to pull the rear cover to see the numbers. OR pop the axle shafts out a few inches,drop the driveline and pull the diff assembly out to inspect it.
The other option is to jack it up and count the turns of the driveline to the turns of the wheel.If it is a no-slip diff, you will need to jack up both wheels.
Most common ratio will be 4:11

The truck has a 350, and 4 speed? on the floor.