OK this may seem like a very simple and dumb question to most of you but I am a little confused. My 78, according to the door plate code, has a Ford 9" non locking rear end with a 3.50 ratio. What exactly does non locking mean? I thought it meant it was "1 wheel drive" but I accidentally romped on it a little to hard in reverse the other day and she laid down 2 good black marks. I've never tried it in D as my tires are brand new. So does this mean that when I'm in 4x4 I really only have 3 wheel drive? I'm pretty sure the front tires both throw mud at the same rate lol. Can someone please clear me up on this.

 

This page may help. It covers differential basics. Your's is the "Standard/Open" type.

http://www.offroaders.com/tech/limit...ferentials.htm

All four wheels are providing acceleration when you are in four wheel drive, even with non-locking open differentials. An open differential always splits the force between the two wheels, however. So if you get one wheel on slippery ice and the other on dry pavement, the most force you can get to the wheel on the dry pavement is the amount of force required to spin the one that is on the ice. Which often leaves you going nowhere and spinning a tire. Push on the gas and you get more rpms and a faster spinning tire, but no more available force so no more go-forward.

Anyway, the article covers the basics well but if you still have any questions give a shout.

 

What is your VIN axle code? I'll check the parts catalog decoder to make sure what you have.

Ford used to offer a limited slip kit for a 9 inch. it retailed for about $150.00. Someone could have added it.

 

Door Plate Axle Code: 16 A

The 16 means Ford 9" nonlocking 3.50 and the A just means tilt wheel and power steering. Unless theres more to it that I dont know yet. Thanks alot for your help.

So are you saying that when 4x4 is engaged it locks all 4 tires? Or if it was in 4x4 and the drivers side tires were on ice and the passenger side on pavement it would just spin the ones on ice? Maybe someone did install a limited slip kit, Ive had it thru some sloppy stuff in 2wd, that 1 wheel drive sounds like JUNK i hope i dont have that lol.

 

16 = Ford 9 inch / non locking / 3.50-1 / 3750 lb front axle capacity

A = Power Steering / Adjustable Column

Does the VIN on the plate match the VIN on your registration? On factory 4x4's, the third digit of the axle code usually ALSO gives the front end type and ratio.


All I said about the possibility of your rear axle having Limited Slip is: Ford made a LS kit that could be purchased over the parts counter. So, if you now have LS, an FO may have added it. Or, someone changed the center section (pumpkin) to one that had LS. These trucks are 30+ yrs old, so who knows what has happened over time.

 

If traction is equal to both tires on the same axle, even an open differential will spin both tires. It is not uncommon to see both rear tires (or front) spin with an open diff. Only when traction becomes unequal does the tire with the least amount of traction spin.
If your truck has open diffs it will only provide power to the tire(s) with the least amount of traction. One tire for the front axle, and one for the rear.
The two differentials work independantly, so it is possible to get power to two right side tires, or two left side tires, or alternating ones front to rear, like right rear, left front, or even two rear tires, and only one front, even the exact opposite, and any other combination.
One thing is for certain, when one tire loses traction, the power is sent to it, and usually a good story abaout how you got stuck follows.
Hans77 provided a good explanation of a differential. (Although Hans77; there is one exception to the "4wd always applying power to all four wheels" theory. A NP 203 full time case has another differential spliting the output from front to rear, and is possible to send power to only one axle in 4wd. With an open diff in the axle, might only see one tire getting power until the center dif is in the 'LOC' position. I know I am splitting hairs here, but it is possible)

 

We could split it even a little further.

Even with an NP203, power is still sent to all 4 wheels. In fact, when combined with open differentials at both ends all four tires are always powering the vehicle evenly between them. It is perhaps the most street worthy 4 wheel drive configuration made.

It's somewhat of a misnomer to say that all the power is sent to the wheel that spins. When in fact both wheels, all four wheels with an NP203, receive equal power even while a single wheel is spinning. Honest. It's just that the maximum amount of force available to each tire is equal to the tire with the least traction. So even though an NP203 mated with open differentials front and rear can still get stuck with just one tire on ice, it will have precisely twice as much force pushing the truck forward as a 2 wheel drive vehicle equipped with an open differential and a single tire stuck on the same ice.

EDIT: Now that I think about it, an NP203 would not have twice as much force. The force should get quartered between all four tires, rather than split between two.

It becomes apparent when you consider that the spinning wheel is dependant upon the opposite tire being planted in order for it to spin. The power is always equalized by the differential.

 

Wow I opened a can of worms here didnt I. Is there a way to tell for sure if my truck has a limited slip kit? I've played around in the mud/offroad a few times and the front seems to fling mud evenly at both tires. Its hard to tell what the back tires are doing though. Like I said earlier it did spin both rear tires in R the other day.

 

A for sure way would be to open the differential and look, but that's a little bit a pain with a Ford 9". The limied slip may behave differently from an open differential with the rear axle jacked up and the tires rotated by hand. But you'll probably need to get a hold of a hard to find install manual to know.

An open differential will cause the opposite tire to spin the opposite direction, for instance. The limited slip may operate the same though. An automatic locker wont spin the opposite tire at all.

Another way would be to get the truck's suspension crossed up on a something like a large rock. With one rear tire in the air, the truck in two wheel drive, apply brake and throttle to induce torque biasing, and see if you can get the truck to move forward. An open differential wont budge. A little finess with the brake and throttle will get you moving forward if you have a limited slip.