Rear Diff fluid change questions

[Plati]

I've got a 2003XLT with limited slip. It leaks out one side shaft seal. I only drive this Beater local and it barely leaks on the short trips (just a drop or two). I take it out on the highway to fully warm it up every couple weeks and it leaks a little more when at speed. Instead of fixing the leak I'm going to just add some fluid every so often when I think it needs it.

I plan to use this stuff since I'm adding in increments
https://www.autozone.com/greases-an...l-synthetic-gear-oil-sae-75w-90-1-qt/1437_0_0

How does one know when its full?
Do you just add until it flows out the fill hole?
Could some please answer this question for me, please?

 

[Trainmaster]

It's full when the grease is level with the bottom of the fill hole.

 

[Black]

Awesome, did you just pull the drain plug or use fluid extractor? I’m trying to keep this as cheap as possible so pulling plug and letting it drain seems to be easy enough

The rear and TC is simple. Open the top fill plug first. Then do your bottom drain plug. The factory uses red thread locker on both so torch them first or you will bugger up the plug (trust me).
Granted they are only $4 each. I replaced both plugs new plugs also come with red thread locker.

Pump one quart in, squeeze in your bottle of friction modifier (8oz I think), then using second quart pump till it just starts to drip out of the fill plug. Should be just shy of 2 quarts.

TC is same process except I did not need heat for those plugs as there was no thread locker and the TC is aluminum. Fill with just shy of 2 quarts of Ford Motorcraft Transfer Case Fluid (use nothing but this fluid) these new TCs do not like the detergents in the multiapplication fluids.

Front differential is a touch more tricky you need to use an extractor in the fill plug to suck the oil out. Can be tough to wiggle the hose past the gears to get all the way to the bottom.

 

[16plati]

The rear and TC is simple. Open the top fill plug first. Then do your bottom drain plug. The factory uses red thread locker on both so torch them first or you will bugger up the plug (trust me).
Granted they are only $4 each. I replaced both plugs new plugs also come with red thread locker.

Pump one quart in, squeeze in your bottle of friction modifier (8oz I think), then using second quart pump till it just starts to drip out of the fill plug. Should be just shy of 2 quarts.

TC is same process except I did not need heat for those plugs as there was no thread locker and the TC is aluminum. Fill with just shy of 2 quarts of Ford Motorcraft Transfer Case Fluid (use nothing but this fluid) these new TCs do not like the detergents in the multiapplication fluids.

Front differential is a touch more tricky you need to use an extractor in the fill plug to suck the oil out. Can be tough to wiggle the hose past the gears to get all the way to the bottom.

I’m not very mechanically inclined, the front diff is only active in 4WD correct? So if my issue is the rear clutch packs sticking is it safe to just do the rear fluid and leave front fluid alone?

 

[Black]

I’m not very mechanically inclined, the front diff is only active in 4WD correct? So if my issue is the rear clutch packs sticking is it safe to just do the rear fluid and leave front fluid alone?

Yes. Just outlining each and their difference as sometimes since you are going to be under there anyway easier just to do them all.

 

[16plati]

Yes it is a quick dump and fill. Well not exactly quick since gear oil is quite thick, Though I would use Amsoil instead of Motorcraft. I have found it to be superior. It is all I use in transmission, differentials, and transfer cases anymore. Motor oil I have not noticed a difference but I also refuse to go past 5k for any oil change so good old Motorcraft is all I really need.
I do differentials and transfer cases at 50k because gear oil is cheap.
Transmissions at 75k.

Are you running auto 4x4????
My old Explorer would do this when tread depths were substantially different for the front and rear. Even with fresh fluid. New tires solved the issue.

This stuff?

 

[Black]

That is the stuff though I have not bought into the squeeze pouch idea.
I have the pump you screw on the bottles. No mess and I reuse the bottle for the old fluid. Putting the old fluid into the pouch seems like a pain.

 

[16plati]

That is the stuff though I have not bought into the squeeze pouch idea.
I have the pump you screw on the bottles. No mess and I reuse the bottle for the old fluid. Putting the old fluid into the pouch seems like a pain.

I saw the pumps at local auto store. Where did you find the amsoil gear lube? Local place?

 

[Black]

Yup. Local NAPA and off-road shop stocks a decent amount.
Pretty sure Amsoil has a stocking dealer locator on the site.

 

[16plati]

Yup. Local NAPA and off-road shop stocks a decent amount.
Pretty sure Amsoil has a stocking dealer locator on the site.

Now I see we use 4.25 pints which equates to 2.12 quarts. I’m assuming I’ll need that 3rd bottle to top it off? I’ll also be adding 4-8oz of friction modifier as well

 

[Black]

I hit the fill plug with just under 2 quarts and the friction modifier.
A quart is a touch over 33 oz. so the friction modifier which is actually a 4oz. bottle is about .12 of a quart.
So 2 quarts of oil plus 4oz of friction modifier is give or take 2.12 quarts. Plus you are never going to get all the old fluid out so buying 3 quarts is a waste.

Put one quart of gear oil in, then the friction, modifier, then top off with the second quart.
That way you get all the friction modifier in there.
The gears mix up the fluid so well you could put it in first if you want.
But I would not put it in last.

 

[16plati]

I hit the fill plug with just under 2 quarts and the friction modifier.
A quart is a touch over 33 oz. so the friction modifier which is actually a 4oz. bottle is about .12 of a quart.
So 2 quarts of oil plus 4oz of friction modifier is give or take 2.12 quarts. Plus you are never going to get all the old fluid out so buying 3 quarts is a waste.

Put one quart of gear oil in, then the friction, modifier, then top off with the second quart.
That way you get all the friction modifier in there.
The gears mix up the fluid so well you could put it in first if you want.
But I would not put it in last.

You just do one 4oz bottle? I’ve seen some ppl saying do 8oz on other forums. Just curious

 

[Black]

I did only use one bottle I had not read other wise for these rigs and the capacities chart in the manual calls for 4oz of XL-3 Friction Modifier fluid.
I also only used one bottle in my Mustangs. I have heard of folks using 2 bottle with the Ford Racing models that have the carbon fiber clutches and the Super Duties.
But I have neither of those.

 

[16plati]

I did only use one bottle I had not read other wise for these rigs and the capacities chart in the manual calls for 4oz of XL-3 Friction Modifier fluid.
I also only used one bottle in my Mustangs. I have heard of folks using 2 bottle with the Ford Racing models that have the carbon fiber clutches and the Super Duties.
But I have neither of those.

Awesome, just picked up 3 quarts of amsoil 75w90 and a fluid pump for $20! Guy behind the counter rang me up for only one quart apparently. Didn’t even realize until I got home to look at the receipt. Now for the friction modifier and some clear weather

 

[16plati]

I did only use one bottle I had not read other wise for these rigs and the capacities chart in the manual calls for 4oz of XL-3 Friction Modifier fluid.
I also only used one bottle in my Mustangs. I have heard of folks using 2 bottle with the Ford Racing models that have the carbon fiber clutches and the Super Duties.
But I have neither of those.

This same stuff you used or do I need the “severe gear”?

 

[Black]

If that is what you bought I am sure it will be fine. Amsoil is a solid product all around. I use the Severe Gear in the black bottle with red cap.
It is formulated for towing, heavy trucks, high performance, and cold temperatures.
I used it many moons ago in my Explorer and it was noticeably smoother and quieter. I have used it in all my differentials ever since.

 

[chuck s]

The bags are the way to go.

The little bottle pumps that screw into standard quart oil bottles will not fit the Ansoil bottles as I found out last month when doing a service on the the Torsen differential in my little Honda S2000 roadster which needs a differential oil change every 15K miles ("severe service") which is every second oil change. This little differential takes less than a quart and the wobbly pump worked albeit needing two hands. My first time using Amsoil 75W-110 which matches the old SAE 90 hypoid gear oil requirement of this car.

This grade of hypoid gear oil certainly ain't grease as it's about the same viscosity as a 10W-50 engine oil.

-- Chuck

 

[Black]

The bags are the way to go.

The little bottle pumps that screw into standard quart oil bottles will not fit the Ansoil bottles as I found out last month when doing a service on the the Torsen differential in my little Honda S2000 roadster which needs a differential oil change every 15K miles ("severe service") which is every second oil change. This little differential takes less than a quart and the wobbly pump worked albeit needing two hands. My first time using Amsoil 75W-110 which matches the old SAE 90 hypoid gear oil requirement of this car.

This grade of hypoid gear oil certainly ain't grease as it's about the same viscosity as a 10W-50 engine oil.

-- Chuck

Do you fill the bags with the old oil??
I have a pump for both small mouth and amsoil larger mouth bottles.

 

[16plati]

Here’s the noise I’m getting. Definitely sounds like rear end. StRts around 4 secs in. Sound up

 

[chuck s]

Do you fill the bags with the old oil?? ?? Only bagged oil I've used came with my new lawn mower.

I have a pump for both small mouth and amsoil larger mouth bottles. Only used Amsoil for this one (1) differential fill and the small pump worked OK but a little clumsy.

-- Chuck