Rear end gearing

[Lattimer]

I was reading another post on gearing, and I was curious....how do you tell what gearing is in the rear? What is the best way? I have no clue what is in my truck.

Can't tell from driving it since I've only driven it about 40 feet and then started tearing it apart.

[robnolimit]

Jack the rear off the ground. Put a mark on the bottom of the tire, and the bottom of the driveshaft. turn the driveshaft, count the turns, until the tire makes one full revolution. You will have to estimate the last partial rotation of the driveshaft. 1/4 turn = .25, 1/3 turn = .33, 1/2 turn = .5 ......... This is not perfect, but will get you close. Common gear sets are - 3.31 - 3.54 - 3.70 - 3.90 - 4.10 - 4.33

[SS Tim]

Good question. The stock '70 gears will be indicated by a code stamped into the axle tube. The stock power team chart below will give you a good idea. However over time many gearsets have been changed but most are probably stock.

Pulling the differental cover and counting teeth is the best way to see what is going on inside and what you have. Then you can confirm the code if it is stock or what has been changed. Any project should have the gear oil changed and inspecting the axles, gears, brakes, ect. is a easy project.

If you have not download the chassis overhaul manual and the service manual too.

http://67-72chevytrucks.com/vboard/s...d.php?t=558016

[truckster]

Originally Posted by SS Tim

Pulling the differental cover and counting teeth is the best way to see what is going on inside and what you have.

I agree. The best way is to pull the cover and count teeth or look at the stamping on the edge of the ring gear. It's going to have two numbers, like 41:11. The gear ratio is simple division: divide 41 by 11 and you come up with 3.727, or a 3.73:1 gear ratio.

The other advantages of pulling the cover is that you can see the general condition of the gears, looking especially for any metal pieces, and you'll also change the gear oil, which is likely long overdue.

[mkmc69]

Where would you find those gear set charts for the other model years?

[SS Tim]

Axle Codes can be found in the Parts Manual.
http://www.2heeldrive.com/Chevrolet/...%20CATALOG.pdf

Powertrain charts are in the Truck Data Books.

Over the past two years I have posted most of these, what do you need?

[Lattimer]

Thanks! One of the jobs on the to do list is to change the rear end oil, so I'll take a look then.

Truck was originally a 6 cyl 3 speed, so from those charts I'm betting on 3.73.

[Lattimer]

Opened it up tonight to change the gear oil. 3.73 it is. Gears look to be in good condition, oil wasn't too skunky.