I see many posts asking: what ratio do I have in my rear end, and does it have a locker? Many codes are deciphered, but on our trucks chances are high the axle or carrier (3rd member) or just the ring and pinion have been changed at some point in the trucks life. This will make any such codes meaningless. Also tags on the axle are often lost at the first axle oil change. I therefore offer the following procedure for checking your axle ratio.

First jack up one rear wheel under placing the jack under the axle on one side. Make sure the other wheel stays on the ground. Then place the truck in neutral. Make sure it doesn't roll away when you do so, but you can't have the e-brake on. So do this on a level surface and chock the front tires and the tire still on the ground in back.

Next mark the tire so you can count revolutions. And mark one of the yokes on the u-joint area of the rear driveshaft.

Now its just a matter of spinning the tire over 2 times (2 times because of the differential action in the rear axle, if you left both tires in the air you would just spin them over once, but you have to make sure both tires spin 1 revolution each, its a lot easier to make one go two revolutions and more accurate) and counting the number of times the input yoke of the rear end spins over.

It is very accurate, so if it spins a 2 3/4 turns: its a 2.75,
Hair under 3 turns: 2.90,
just over 3 turns: 3.08,
3 1/4: 3.25,
3 1/2: 3.5 or 3.54 or 3.55,
3 3/4 3.73 or 3.75,
just under 4: 3.90,
just over 4: 4.10 or 4.11,
just over 4 1/4: 4.27 or 4.3
just over 4 1/2: 4.55 or 4.56
just under 5: 4.88
just over 5: 5.13

that's as high as I'll go but you get the point. If there is a choice of ratios the choice is not yours, it depends on the axle. For example, if you get 3 1/2 turns, if you have a 9" rear end, then its a 3.5 ratio. If you are checking a Dana 44, its a 3.54 ratio. If you are checking a Ford 8.8, then its a 3.55 ratio. On some ratios I didn't list all possibilities for all axles, just the common ones, if you really need to know the exact axle ratio (rather than within .02 or so) then look at the choices for that axle in a parts book, for any given axle there will only be one choice in the correct range.

Now one wierd thing could have happened, either you couldn't budge the wheel (make sure you are in neutral and the e-brake is off before you get excited,) or you heard a racheting sound. This means you have a locker in the rear end. Either a Detroit Locker or a Easy Locker or a Lock-Right. To check the ratio on these axles, jack the center of the diff, spin one of the wheels over once and the other will automatically spin over exactly once, also. Count the revolutions of the input yoke as above.

If the above didn't happen your only choices left are limited slip, open diff or Air Locker. If it has a air tube running into the diff, then its a switchable Air Locker.

Otherwise jack up the rear end with both wheels in the air. Put the truck in Park or in gear. Now spin one tire forward. If the other one spins backwards then you have a open diff or a limited slip with worn out clutches, which is the same as an open diff. If the other tire either remains stationary or moves the same direction as the other tire, then you have a functioning limited slip differential (Trac-Loc or other kind)

Hope this has been helpful.

fordmando
78 F-150 4x4 400 4 on floor
86 Nissan 300ZX
George