Just purchased 1990 1/2 ton 4x4. I am interested in what factory gear ratios I have? I don't know where to figure out without pulling diff covers. I have the 5.7ltr and 4spd manual trans.
There is a way to get a rough estimate. On a lift mark the top of the tire with chalk Mark the differential to drive shaft with chalk Rotate the drive shaft as many times as it takes to get the tire to rotate one turn. If it turns a little over 4 times its 4;10-4.11 under 4 turns you would have to figure out 1/2 3/4 turn etc and see what ratios they had in that year and figure which is closest TO do it exactly pull the cover and on the ring gear will be marked teeth for pinion and ring gear / divide the ring number by the pinion number ( teeth )
Just check the tag off of one of the diff cover bolts, little metal tab will tell you gear ratio if it's still there, I would bet money they are 3.73's though.
Somewhere on the driver's door or body area of your vehicle you will find a sticker that has the VIN across the top, GVR, tire size, and other information on it. At the bottom of that sticker it will show an "axle code". Take that information with the VIN number to any dealership and they can get the gear ratio and tell you what type of rear axle is in the vehicle. SOMETIMES, if you crawl underneath the truck, there will be a tag on the rear axle cover (held on by a bolt) and the gear ratio will be stamped into the metal tag.
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