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Any way to tell if I have limited-slip?

11K views 24 replies 12 participants last post by  tbolt 
#1 ·
Is there any way to tell if I have a limited slip differential or not?
How about the gearing? Any way to tell if I have a 3.73 or a 4.10?
 
#2 ·
I have a web site that will tell me off the code on the door sticker . I know the gears might have been swapped but oh well .If not jack it up put the trans in neutral and try and turn the tire that is off the ground by hand.
 
#3 ·
look at your tag on the cover that is held on with one of the bolts, it will say your gear ratio and followed by a L if its limited slip. Thats if no one as changed anything but when i change things in the axle different from the tag i remove it.
 
#4 ·
The most common i have seen...

only the FX4's have the limited slip rears.

grab the last 8 of your vin, and axle code.. incase. and call your local ford dealer and ask them if they can look it up.

or, if you have stock tires... 2,000RPM in OD will be about 68-72 mph. with 3.73's.
1,500-1,700 rpm with 3.55's is around 68-72 mph
2,200-2,500 rpm with 4.10's is aorund 68-72 mph.

ha ha, ive got 3 trucks here... 150 w/3.55, 250 gasser w/4.10, 350 diesel w/3.73.
 
#8 ·
the tags says:
S 409 F
L731059K12

So anybody know what it is? p.s. the dealer did not know what the gearing was either and if it was limited slip
 
#10 ·
That IS with the tag completely removed...I checked and there is no character in front of the L...I'll take a picture if you want.
 
#14 ·
How much friction modifier goes in the case? They gave me a 4oz bottle but I got two bottles just to make sure I had enough.
 
#15 ·
How can you actually test to see if it is working or not?
 
#18 ·
I see you figured it out but here is a way to tell if the tag is missing. Jack up both rear tires and spin them, if they both go the same direction it is limited slip, if one goes the other way its not!
 
#25 ·
The tag (on the diff cover) on mine reads; 3L73 most likely a dually has 4.10's so it should be 4L10 Check your wheel brgs also. The clutches may be chattering, change diff fluid and add the friction modifier 8 oz

to test if it's working try this

 
#24 ·
:whs:
 
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