Fluid for L/S differential?

[bobflood]

'97 5.0 2WD EB; 238K miles. Working fine, but I am planning to replace the fluid in the differential for the first time. Axle code is D4, which says it is limited slip. Have searched the threads, but am unclear as to the need to add "friction modifier" to "75W149 Mobil1 Synthetic LS" lubricant? Do I need it or not?? I would appreciate any advice from this Explorer braintrust.

 

[gmanpaint]

http://www.explorerforum.com/forums/showpost.php?p=2401413&postcount=2

 

[bobflood]

Gmanpaint - Thanks for the info. Are you suggesting that I leave it alone since everything is working all right and it says it's "lifetime" lubricant? Almost a quarter-million miles on the same stuff is making me nervous.

 

[my pos mounty]

I am sure that Gmanpaint was not suggesting that you leave diff fluid in if it has 250,000 miles on it. There really is no such thing as a "lifetime" lubricant, call Ford and ask them how long their "lifetime" is for that diff lube and if they will stand behind their claim.

Use 75/140 full synthetic Lubricant. Mobil1 may not need the friction modifier added to it.
I would not bother to add it initally, if the LSD clutches chatter when cornering at slow speeds, then I would add a few ounces..wait for a few days to see if the chatter disappeared, if not, add another few ounces until it no longer chatters.

 

[sean99]

Amsoil Severe Gear 75w-110 is a good option.

 

[gmanpaint]

Simply showing you some info on the subject.

All it takes is a contaminant, such as water to break the fluids down. Regardless of how old or new the fluids are. Water can seep in from the axle seals the day after it has been changed and ruin it. Driving in deep water over the dif housing can allow water to get in from the vent tube if it has a faulty breather cap. High temps for prolonged periods of time can break down the fluids. Synthetics take the heat better than dino.

As you can see, there are variables that bring upon the needs to install fresh fluids, especially if you do not know the entire history of the vehicle.

There are limitations to "All" fluids. If your not sure, and want peace of mind, by all means, replace the diff fluids. This will do no harm of any kind. Full Synthetic will need no additive for a LS. A hybrid dino synthetic may, and full dino fluid will take an additive.

75-140 full synthetic is my recommendation for your D4. Clean out the dif housing with rags and sweep a magnet inside it, paying special attention to the catch basin on the bottom. Look at your gears for for burnishing, look for signs of your LS clutch discs failing. Take the necessary actions to repair anything you suspect is wrong, or refer back to the forum for more help.

Your manual will tell you the proper amount of fluids for everything, or search the forum for more info.