Differential fluid

What weight gear oil should I use on my front and rear differentials on my 86 f350? I know the front is a d60 not sure what the rear is... What did this year come with for a rear end? Did they come factory as limited slip?

85W-140 for the Sterling 10.25 rear, if memory serves. Get a rubber gasket (no scraping off RTV on the next fluid change) while you're at it and check the vent tubes to make sure they aren't packed with gunk.

Check the diff codes in the Tech Introduction sticky at the top.

Check your rear axle tag and then figure out if you're diff is open or limited slip. Open should take 85W-140, I'd recommend at least semi synthetic if you are going to tow at all. And you don't need a gasket, I've never seen one on a Sterling, just goofy goop.

You can also just pull the diff cover off and inspect as long as you have another rig to get you to the parts store. I'd like to think folks always update the tag if they make a gear/carrier change but experience tells me otherwise, and cracking it open will answer all the questions with little or no mystery

lotzagoodstuff said:

And you don't need a gasket, I've never seen one on a Sterling, just goofy goop.

Click to expand...

They're not needed but it makes future fluid changes a bit easier, no RTV boogers to clean off.

lotzagoodstuff said:

Check your rear axle tag and then figure out if you're diff is open or limited slip. Open should take 85W-140, I'd recommend at least semi synthetic if you are going to tow at all. And you don't need a gasket, I've never seen one on a Sterling, just goofy goop.

You can also just pull the diff cover off and inspect as long as you have another rig to get you to the parts store. I'd like to think folks always update the tag if they make a gear/carrier change but experience tells me otherwise, and cracking it open will answer all the questions with little or no mystery

Click to expand...

I hate to sound stupid but when crack it open how can i tell if its limited slip or open?

Sorry to be confusing: "crack it open" means take the differential cover off and see what ring and pinion is inside. You can count the number of teeth on the ring gear and divide by the number of teeth on the pinion gear to get the exact gearing, and you will be able to see if there's a clutch pack inside which would indicate limited slip, if there's just spider gears in the center of the carrier (or you can turn one wheel independently of the other) then it's an open rear end. I'm sure you can find lots of pictures or a diagram of a limited slip carrier vs open diff to identify what you have, and it will most likely match the id tag.

I would inspect the old gear lube that comes out for excessive metal fragments, and clean everything out with brake cleaner before you put it back together and fill it with new gear lube.

Lastly, don't get any gear lube on your coveralls: it stinks (literally).

Good luck

Thanks for the info. How many quarts will my axles hold?

im pretty sure that my owners manual says 80-90.thats what im running.

Going of memory. Rear is like 4.5 quarts I think. Front is 3. Something like that.
Parts store can tell you.

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I have 80W90 in my D70U at the moment. It's what my manual said came in it, and I had it on hand already.