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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks Discuss the Early Eighties Bullnose Ford Truck

Limited slip?

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Old Jun 20, 2021 | 08:08 AM
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Limited slip?

My door jamb data tag is gone on my truck. I’m trying to determine if I have a limited slip differential. It’s a 1982 F350 dually. The axle looks like a Dana 60 to me. I noticed that when both wheels are off the ground and I try to spin one side, it is very hard to turn and the other wheel spins too. My guess is I do have limited slip. Is this a logical conclusion? Is there a cast number on the differential housing anywhere that would help me identify it? Could it be a Dana 70HD? What is the difference between model 60-3, 61-1, and 61-2 in the manual? Need to know because friction modifier is required if limited slip.
 
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Old Jun 20, 2021 | 08:13 AM
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There should be a tag under one of the differential bolts for the cover. But sometimes they are missing. If the other wheel spins the same direction when it's off the ground, then you probably do have the limited slip option.
 
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Old Jun 20, 2021 | 08:23 AM
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You may not need the friction modifier as most gear oil is marked for LS.
Now I would fill it but leave a little room just is case you do have to add the friction modifier.

If you do have LS and start driving it, if you get chatter from the rear axle when turning a corner under power then you add the friction modifier.
My Durango does this after a 30 min run (or more) on the high way. Stop at the end of the ramp to make the turn and when under power it will chatter.
I wanted the dealer the other day to see if there was room to add friction modifier but all they did was check the level and I dont think they did that as I did not see them at the rear long enough to do so.
Dave ----
 
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Old Jun 22, 2021 | 08:20 AM
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I always add one bottle of Motorcraft friction modifier when changing gear oil on LS equipped trucks.

It is $9 from the dealer. Cheap insurance methinks.

I have had good results with Redline 75w-140 full-synthetic in the Sterling 10.25. Might have even gained .25 MPG!

on the other hand, I have heard over and over again that most of the limited slip clutches are all worn out after 100-150k or so...
 
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Old Jun 22, 2021 | 01:42 PM
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If the gear oil says for LS on it that does not mean that it has the additive. It may only be compatible with the LS additive. If you have LS use the specified additive.
 
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