I put 3.00:1 rear diff in my truck anbd now 4x4 doesn't work. Front diff tag says 3.00 on it and the rear didn't have one. Had to change rear end in the summer when it blew out on hwy 2 south of airdrie. Pin had a major stress fracture. Any help, info?

 

Did you confirm (Physically Identify) both axles.

BTW, your engine >

there ISN'T an M after 400.....The M goes with the 351M.

 

I have physically confirmed the rear (13 teeth pinion, 39 on ring)

I have taken the front apart. I don't want to touch it until I have the neccesary items. IFS is fairly involved to pull. The factory tag on the front diff states 3.00 so that is why I put 3.00 in the rear. I didn't know that that was wrong at the time. I didn't realize that I had a problem with it until now ( winter). My front end is binding an all I can think of is that I changed the rear

 

See my reply to your question in this other thread.

https://www.ford-trucks.com/forums/s...hreadid=192322

Please don't cross post the same question in more than one thread.

 

To determine gear ratios without the tag
Jack up rear end and place on jack stands. Place the gearshift in neutral.
Have 2 friends turn both rear wheels until the tire valve stems are in the 12 o'clock position (straight up)
Place a mark on the driveshaft with chalk.
Have your 2 friends turn the rear tires 1 complete revolution in the same direction at the same time (slowly)
Count how many revolutions the driveshaft turns for 1 complete revolution of the tires.
If your gearset is 3.00 to 1 , your driveshaft will turn exactly 3 turns to one turn of the wheels.
If it turns a little over 3 turns, it's a 3:07 or 3:08
3.5 it,s a 3:50 or 3:54 or 3:55
3.75 it"s a 3:73
a little over 4 turns, it"s a 4:09 or a 4:10


4.5 =4:56
4.75=4:88
Now do the same to the front end with the hubs locked in and the transfer case out of 4wd.
Both the front and rear ratios have to be the same or they will bind up until something breaks.
On F150's and broncos, Ford mixed and matched spicer/dana axles (front) and ford axles (rear) with slightly different ratios, (3:54 front, 3:55 rear) etc.
The difference being so small, it did not affect driveability.
Let us know what you come up with.
Good luck!

 

if the front is 3.00 will the rear be higher - like 3.08 or something?

 

Front and rear ratios should ideally be the same.

The only reason they are different from the factory is when the two axles don't have an exact matching ratio (usually because of the difference in ring gear sizes). Then you get combinations like 4.09/4.10 or 3.55/3.54 or 3.07/3.08, etc.

Since the 9-inch rear axle that the factory installed in your truck had a 3.00:1 gear set available, there's no reason your truck shouldn't have 3.00:1 in both axles.

 

thanks guys,

My fear is that it is like a 3.50 or 3.54 or 3.55 and I won't know which to pick but I will give the tire thing a try.


thanks again,
Chuck

 

To answer "the question" the front will always be overdriven if the ratios must differ!
This is done to keep the vehicle tracking straight.
Example: Front 3.54 Rear 3.55
One exception would be mud bogging where they would use large tires in the rear, small tires in the front.
Then they would run something like 4.88 rears, 4.10 fronts because of the extreme difference in sizes!