Drivetrain Specs

[pamelaosburn]

I need to buy a new rear end and transmission for a 1985 Chevy Silverado Truck. It has a 700r4 transmission.
I need to know the gear ratio before I can order my rear end. They are not listed on my truck.

[Jason S]

Do you still have the Service Parts Identification decal in the glove box?  There are codes on the decal the should have that information. 

Ultimately the only way to know for sure is: Pull the rear cover off the differential (also a good time to change the gear oil) and count the number of teeth on the ring gear and count the number of teeth on the pinion gear.  Divide the ring gear tooth count by the pinion gear tooth count and that is the differential gear ratio.   

You can also get pretty close to finding out the gear ratio by taking the trucks weight off the rear tires (jack up the axle on each side) and watching the driveshaft (or pinion yoke).  Turn either side wheel, as you are turning the wheel count the revolutions of the pinion until the wheel has completed one complete revolution. It can be helpful to mark the tire to ensure it goes one full revolution. If the pinion turns almost 3 and 1/2 times, it is likely a 3.42 gear ratio. If the pinion turns just over 3 and 1/2 times, then it's probably a 3.73 gear ratio.  Be sure to block the truck so it doesn't roll once the rear tires are off the ground.

[bake74]

I need to buy a new rear end and transmission for a 1985 Chevy Silverado Truck. It has a 700r4 transmission.
I need to know the gear ratio before I can order my rear end. They are not listed on my truck.

     I see this is your first post, welcome to the site from California.
     Why do you need to buy a new rear end ?  Did you destroy the ring gear or pinion gear in the rear end ?  Otherwise as Jason S said, take off the rear pumpkin cover and figure out what ratio it is.     (sometimes it is easier and cheaper to rebuild a rear end then find one in working order )
     One important question, is this a 2wd or 4wd ?  Hopefully you know this, on a 2wd you can change ratio's (unless you want the same).  On 4wd you need to match the front end and rear end.  Hopefully you knew this and I am just reminding you.