I got my 87 Ranger as a gift. I forgot to check the gear oil and it bit me in the butt. I now have to rebuild or replace my rear end but the only problem is before I got it some one removed the the axle tag on both the front and back and the drivers door has been replaced. I don't know what the gear ratio is. Is there any way I can find out the gear ratio?

 

You will need to count the teeth on the Ring, the larger gear powering the axles
And count the teeth on the Pinion, the smaller gear connected to the Drive shaft

Then go here: Ring & Pinion Calculator
And enter the numbers

Front and back will, of course, be the same.

I would see if you can find an L/S(limited slip) replacement vs an OPEN, L/S came in all the popular ratios
L/S is Fords version of Positraction(GMs version of L/S, lol.)
OPEN means only one wheel gets power, and the easiest wheel to spin is that one wheel

You can look here: http://www.therangerstation.com/tech...le_codes.shtml

Get the door code numbers and hit the wrecking yards for a match.

So say you have a 7.5" 3.73 now
You would want to find a Door Code F6, L/S, 7.5" 3.73

 

Thank you and just as a curiosity is there anyway to find out without dissembling it?

 

should be able to take VIN to dealer and they can look it up

 

I doubt Ford would have that info for an '87 vehicle
And the VIN number itself doesn't, serial number in VIN would, but that's the info Ford only keeps for about 10 years, but it is a FREE phone call.

If axle tag and door label are gone then no, there is no other way to get ratio.
Any numbers stamped on the housing will be about the housing itself not the internal gear ratio since the housing is the same regardless of ring and pinion set up inside.
You can get the gear count just with back cover removed.