How the heck am I supposed to know if I have a limited slip differential? I'm changing my gear oil and the owner's manual says I need to add a hypoid gear oil additive friction modifier if I have a limited slip differential. I own a 1993 Dodge Dakota LE, 5.2L.

Thank you!!

 

If you have the cover off, post a pic.

 

what? No. Why would you tell him that?

Op, jack the rear end up. Turn the tires while in neutral. If they spin the same way, its an LSD. If they spin the opposite way, its an open diff.

 

Because a picture is worth a thousand words.

 

its also wasted time for the op and him not learning the quick and easy way to find out.

 

Well, I had read in another thread about spinning the wheel. I did that and my rear wheels turn in opposite directions so that tells me I have an "open" differential and NOT a limited-slip differential. But, the cover was already removed so I took a photo for our collective enjoyment.

 

Also, how do I know if I have a 7-1/4 or 8-1/4 axle?

 

Yep, that's an open diff.

Axle size is determined by ring gear diameter. So, you can measure it, or, they can also generally be identified by the number of cover bolts, and the shape.... There are pics available out there in the world.

 

Thanks, Hey You. I knew it was the diameter of the ring gear but it aint easy to measure. I have a ten-bolt cover. Maybe I can dig it up. Thanks a bunch for your help.

The owner's manual says the differential gear oil doesn't ever need to be changed under "normal" conditions (which is how I classify my truck). But I aint buying it. My truck is 24 years old with 170,000 miles on it (original owner) and have a hard time believing gear oil doesn't break down after 24 years. Condensation possibilities alone would make me skeptical. This is why I decided to change it. It was "serviced" once in 1999 but I suspect all they did was suck out the old gear oil and add new. They probably did not take the cover off. I did. And the magnet on the bottom had a good layer of crud on it so I cleaned it off. It did not appear to be shavings unless they were super fine. It was more like old grease. Glad I pulled the cover off and did it the right way. Just need some Permatex Gear Oil RTV to finish the job. Don't think I'll use a gasket. I'll just use the RTV.

 

I have a 8.25 sitting in my driveway..... Its 10 bolt cover and if you measure from the top bolt to the bottom bolt, it is about 9.5 in. I would "think" a 7.25 would be about a inch less. FWIW I doubt mopar ever put a 7.25 in a 4wd v8 dakota. I bet yours is 8.25