<!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <wontGrowAutofit/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--> I am going to change the differential fluid on my 97 F150 2wd 4.2L V6 and had a few questions:

1. Do I need to put any kind of additive into the replacement fluid?
2. I have heard Synthetic replacement fluid is good and bad, which is it?
3. How much replacement fluid should I need?

My truck has 149, 000 miles on it and, to my knowledge, has never had the differential fluid changed. Is there anything I should to know?

 

The axle tags say to use synthetic. Don't know if it's totally necessary, but given that you don't really ever change the fluid it's probably not a bad idea. That said, the synthetic is WAAAY expensive.

I believe your truck uses the 8.8" gear differential (you can tell if you have 10 bolts on the diff cover). If so, it takes about 2.7 quarts of oil.

If it's posi-traction / limited slip differential you'll need a little bottle of friction modifier. There's probably a way to tell if it's limited slip other than opening it, but once you open it you can tell by the Z spring in the middle of the differential. If it's there, you've got posi-track, if not, you don't... (here's a photo of a posi-track just so you know what I'm talking about Ford Racing 8.8 Rear 31 Spline Trak-LOK Limited Slip Differential (97-03 F150) at AmericanTrucks.com - Free Shipping!

 

you can get 75 w 140 full synthetick GENERIC gear lube at Wal Mart for about $10. a quart. IT is good stuff. IF you have the LS unit you need the friction modifier. YOu code on the alxe will have an L with the ration to designate that. --- 3.55L---.

 

look at the sticker on the drivers door


Axle Codes
L - Limited Slip Differential
C - Conventional Differential
Code Ratio
18 3.08C
19 3.55C
24 3.54L
25 4.10C
26 3.73C
27 3.31C
28 3.73C
B5 4.10L
B6 3.73L
H9 3.55L

 

Buy Mobile 1 full synthetic LS 75w140. It already has the limited slip additive in it. Available at most parts stores and is not that much more than the generic stuff.
You will need 3 quarts. Buy 4 just in case and then you can take one back unopened.

By the way, Ford does not recommend ever changing the fluid. It is filled at the factory with full synthetic and unless you have a problem, there is no service interval.

Having said that, I change mine every 100,000 miles. They also don't recommend removing the rear cover. Just pump the old out and the new in.
I found the best way is to get a drill adapter oil pump (like the ones used for oil service on boats). It has a small tube and will reach down to the bottom of the housing. Will take a little time to pump it out as the oil is thick.

Good luck.

 

If my memory is correct, I believe the Haynes Manuel suggests changing it every 24 months...Are you sure Ford does not recommend ever changing the fluid?

 

I am sure. Look in your owners manual. There is no service period. I actually talked to one of the mechanics at the dealership about this and he said that is true. It is synthetic from the factory and no service is needed for the life of the vehicle unless you have submerged the axle and the potential for water in thru the vent tube is present. Then you pump out and refill. Only time they remove the rear cover is if they have to replace hardware.

 

Like if you have leaky axle seals that need changing like mine.

 

If you get a good synthetic, no friction modifier additive is needed, contrary to what is stated earlier. If you have to add a friction modifier, it does not meet your vehicles lube standards and should not be used anyway.

Royal Purple, Mobil1, and Valvoline all meet the necessary requirements, and so long as the API ratings are at least as good as what your owners manual recommend (or a TSB if applicable), then it will work without any extra friction modifiers.

For the record, contrary to the fact that Ford has not specified a replacement interval, wear and tear does occur, and the extreme sheer stresses, heat, slippage, and corrosion all take their toll. Replacing the fluid is a good insurance policy against all those things. I've heard people claim the trans fluid is good for 100,000 miles. Notice all the failures on 5R55e transmissions. See a connection? Replacing the fluid gets rid of all the contaminants, which are otherwise trapped in a closed system.