my truck is a 04 f350 srw. The door code says 3.73. Here are the numbers off of the rear end tag. line one V 423 F. line 2 L 73 10 5 4D21. Help please.

 

Looks like a 3.73 limited slip to me but the axle code doesnt match the tech folder above. . . guess thats why you're asking. I really dont know enough about the codes but I 'spect the L73 in line 2 is the winner.

 

I am going to agree with TwelveAlpha here, I would guess 3.73LS. What engine do you have, cause pretty much the only rear gear ratio for the SRW diesel is 3.73.

 

thanks. what was throwing me off is the 423 in the top line

 

6.0 diesel

 

Ford has only offered three ratios in the Super Duty that I know of 3.73, 4.11, and 4.30. So I'm guessing the 423 is just part of a part number or something else.

Now that I'm looking at it again though, are you sure it doesn't say 3L73 on the second line and maybe the 3 is covered up by the bolt or something? Cause I think that 3L73 is one of the markings for the 3.73 LS rear end.

 

Here's the 'shade tree mechanic' way of finding out without cracking open the rear differential & counting teeth....

1. Jack up the rear end so that both rear tires are off the ground.
2. With a marker, piece of soap stone, chalk, tape, or whatever you happen to have, clearly mark the position of the rear driveshaft and one or both rear tires. It is generally the easiest to mark the point that is closest to the ground (i.e. straight down), and to mark the inside of the rear tire(s).
3. Put the transmission and/or transfer case in neutral.
4. Start turning one of the rear tires by hand while watching the marks on both the tire(s) & the driveshaft. What you will want to do is count the number of rotations of the driveshaft for each single rotation of the rear tire(s).
5. At this point, the numbers are pretty self explanatory. If you have 3.73 gears, the rear driveshaft will turn almost 3 3/4 times for one turn of the rear tire. 4.10's would be a bit over 4 turns, etc.
6. On a side note, if you have limited slip, the rear tires generally spin in opposite directions while you are doing this; there is the possibility that the clutch pack is worn out, and this could change this expected behavior. An open differential will typically let one tire rotate while the other stays in the same place.