Got this out from under my truck
S869C
L55 88 8H03
Axle code H9


How many quarts or pints do I need of gear oil and I belive I need 4 oz of friction modifier from ford right?

The only oil I can find around here is mobile 1 for $15 per quart and walmart brand super tech for $10 per quart. Can anyone recommend a place to get some at?

 

Front Axle
Note: 9.525 mm (3/8 inch) below the bottom of the filler hole 3.5-3.7 pt (US)
Rear Axle
Note: 6-14 mm (1/4-9/16 inch) below the bottom of the filler hole 5.5 pt (US)
Traction-Lok 4 oz (US)
^^^
The above info is for a 1998. You also have the limited slip 3.55 8.8 (I think) rear end.

Hope this helps.
Mike

 

Thanks. Basically I need just over 3 quarts.

 

You missed the 1st digit on the 2nd line, which in your case is "3".

 

I am getting a bit of a whine when cold. It goes away when it gets warmed up so I was going to change the fluid. Its a 98 with 93k miles on it. Easy miles, no submersion and limited towing.

The redline synthetic says it doesnt need the friction modifier. Should I put it in anyway or just use the redline?

 

Does Redline's warranty pay for a new diff & installation if their oil trashes yours?

I'd use the right stuff.

 

The 8.8 uses 2.75 quarts.If it has L/S you will need 4oz of friction modifier.If the fluid says it has the modifier in it still put in 4oz.Wal-Mart brand is ok to use.You can get Royal Purple for $10.00 a quart at Pep Boys or NAPA.I prefer to use a gasket along with a little bit of RTV.The gasket number is;
FelPro RDS 55341
After installing the fluid go to an open parking lot and do a few figure "8s" to get the modifier and fluid thru out the axle.

 

Thanks for all the tips. I am going to order redline. I can get it for $7.95 per quart online and I will pick up the friction modifier from the ford dealer. Better safe than sorry.

 

Another thing to look at is the oil viscosity. I believe in 98 and at least up to 04 they stated to use 75w90. Ford since has changed their requirements. They now state to use 75W140. I believe for all 8.8 and 9.75 diffs. If I am wrong, someone please correct me.

 

The tag on the rear end said 75w-140 only. I noticed on redlines webite they sell the friction modifier for $5 for a 4 oz bottle. It says its not needed for the 80w140, its already included in it. I guess I should order the modifier and put 4 oz in it anyway?

 

97+ spec on the rear diff is 75W140.
FWIW the friction modifier is used to allow the clutches to slip when the rear wheels are turning at different speeds. Without it the clutches tend to slip and grab, slip and grab. This is what causes the clattering noise sometimes heard.
If it is already in the oil from the refinery weather you add it or not is up to you. Personally I don't add it when it is included.


JMC

 

Add it!

 

I just ordered the redline. Maybe it will be in in a few days and I can change it this weekend.

 

One question, friction modifier is only needed in limitied slip (posi) diffs, not open diffs in these, right?

 

That is correct.